Some organisms only parasitise humans in exceptional situations. Generally the infection is due to a coincidence. Nevertheless, infection with a thorny-headed worm, for example, may have a fatal outcome. Some parasites only occur in certain well-defined geographical areas and are only of local importance. One example is oesophagostomiasis. Doctors in Europe will occasionally be asked about parasites. Often people say they have noticed "something" in their faeces or in their skin. Sometimes this is an actual infection, such as finding proglottids in underwear, cutaneous larva migrans or an accidental myiasis on a small wound. Alternatively, it may only be a pseudoparasite, e.g. an earthworm which arrived by accident on the place where faeces were deposited. This is quite different from parasitophobia, a persistent psychiatric disorder, in which sufferers are convinced that they are being besieged and attacked by various parasites, or that they are present in their immediate surroundings. Below is a check-list of organisms which have not been included in the chapters on worms, schistosomiasis or filariasis. A number of "unusual" worms sometimes make their homes in our bodies. Many of the following worms will be a once-in-a-lifetime event for most doctors.

The nematodes Agamomermis hominis oris and Agamomermis restiformis belong to the Mermithida. They are both pseudoparasites. No authentic infections in humans are known. In the wild there are several species of Mermithida which parasitise insects. For this reason related species are studied as part of vector control (e.g. Romanomermis sp. to control mosquitoes and simulids).

The nematode Anatrichosoma cutaneum belongs to the Trichuridae. The parasite is related to Trichuris trichiura. It usually infects monkeys (Macaca mulatta) where it is found, among other places, in the nose. Infections of humans are exceptional (e.g. cutaneous creeping eruption). One unusual feature of Anatrichosoma sp. is that the male parasites, although they are just as long as the female worms, are extremely thin. During copulation the male pushes its rear part, sometimes half of its body, into the female.

For Angiostrongylus sp., see Parastrongylus.

There are two important species : Angiostrongylus cantonensis (provokes eosinophilic meningitis) and Angiostrongylus costaricensis (appendicitis-like syndrome).

In 1938, Angiostrongylus cantonensis was discovered in rat lungs by Chen in Canton, China. Recently, the taxonomical position of the worm as changed and A. cantonensis has been transferred to the genus Parastrongylus, but in this text we will continue to use the generic name Angiostrongylus. Infection with A. cantonensis is the most common etiology of eosinophilic meningitis. Do not confuse this with disease resulting from infection with Angiostrongylus costaricensis. Angiostrongyliasis occurs primarily in Southeast Asia, throughout the Pacific Bassin, including Hawaii, Indonesia, Philippines, Japan and Papua New Guinea, but also in several Caribbean nations (Bahamas, Cuba, Puerto Rico, Dominican Republic, Jamaica). Few cases were discovered in Ivory Coast and Egypt, Madagaskar, Mayotte and Reunion Island. There was even one described case in North America. A large percentage of the rats in New Orleans were found to be infected with Angiostrongylus cantonensis. Occasionally, small outbreaks occur.

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Angiostrongyliasis (infection with A. cantonensis, the rat lungworm) has an incubation period of 2-35 days. Symptoms are due to migration of the larvae in the brain and the inflammatory reaction which occurs. The disease presents with acute moderate to severe headache (100%). Besides the headache, patients can complain of eyeball pain. Visual problems can occur, due to involvement of one or more cranial nerves (diplopia, acute strabism, gaze palsy) or due to migration of the larva into the eye, which can lead to retinal detachment and blindness. Facial nerve paralysis occurs occasionally. Nuchal rigidity occurs in about 66% of patients and Brudzinski’s sign is present in ±66%. Transient ataxia can occur. Delirium, seizures and cognitive dysfunction have been observed. Hyperesthesia in various dermatomes occurs. Paresthesias of arms and legs, trunk or face can persist for months, although chronic disease is rare. Vomiting and nausea are self-limited and stop after a few days. Oedema (generalized, legs, facial or migratory) occurs in a minority of patients. Fever occurs in less than 50% of patients. The disease tends to be more serious in children. The disease is self-limiting. Most symptoms disappear spontaneously within 4 weeks of onset (range 2-8 weeks). Mortality is less than 1%.

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Eosinophilia of peripheral blood or CSF is not always present on initial laboratory testing. Pleocytosis may be absent early in the course of infection. Larvae are rarely detected in the CSF. Beware of fibrin treads which can mimic larvae. The CSF can be clear or cloudy, but does not contain blood (except in case of a traumatic tap of course). The absence of focal lesions on CT or MRI-scanning of the brain distinguishes A. cantonensis infections from most other helminthic infections of the brain. Enhancement of the meninges and globus pallidus (basal ganglia) can be noted on MRI. Immunodiagnosis is possible in some centers. There is a poor correlation between the serological results of serum and CSF.

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Analgesics are usually needed. Steroids (e.g. prednisolone 60 mg/day x 2 weeks or dexamethasone) shorten the duration of the headache. When performing a spinal tap, the opening pressure is increased in about 60% of patients (average 23 cm water; normal 10-20 cm). Many patients notice an improvement after a spinal tap. Repeated spinal taps to reduce the intracranial pressure are sometimes performed. Antihelminthics are thought by some not to be effective and considered to worsen the symptoms, probably because of the inflammatory reaction to antigens released by dying worms. Some clinicians use mebendazole or albendazole, but controlled studies are lacking.

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The differential diagnosis of eosinophilic meningitis includes the following :

• Angiostrongylus cantonensis (main cause; synonym Parastrongylus cantonensis)
• Gnatostoma spinigerum
• Toxocara canis and T. catis : visceral larva migrans
• Baylisascaris procyonis (normal host is the raccoon, Procyon lotor) and Baylisascaris transfuga (round-worm of the bear)
• Taenia solium, though in the majority of neurocysticercoses the cerebrospinal fluid is normal
• Fasciola hepatica and Paragonimus sp. (ectopic localisations)
• Filaria: Loa loa (specially severe reactions after DEC treatment), Meningonema peruzzi (monkey parasite)
• Strongyloides stercoralis in hyperinfection syndrome (beware steroids)
• Trichinella spiralis (massive infection)
• Myiasis due to Callitroga hominivorax or Hypoderma bovis
• Coccidioidomycosis and cryptococcosis
• Non-infectious origins (lymphoma, medications, ventriculoperitoneal shunts)

Herring worm disease may be caused by various nematodes. Anisakis simplex and A. physeteris (herring worms), Pseudoterranova decipiens (syn. Phocanema decipiens or Terranova decipiens; cod worm or seal worm), and Contracaecum osculatum are all nematodes belonging to the Anisakidae. They can cause infections in humans who eat raw or insufficiently cooked saltwater fish. The possible medical importance of Hysterothylacium (Thynnascaris) is to date unclear. Adult A. simplex have been found in the stomachs of whales and dolphins. The eggs are eliminated with the faeces. In sea water the eggs hatch after embryonation, after which the released larvae penetrate small crustaceans e.g. copepods or krill (Euphausia), which then in turn are eaten by fish or cephalopods. Herring (Clupea harengus), salmon, hake (Merluccius merluccius), anchovy (Engraulis encrasicholus), sardines (Sardina pilchardus), codfish, flounder, haddock, mackerel (Scomber japonicus), Japanese inkfish (Todarodes pacificus) and monkfish are frequently infected. The parasites attach themselves to the gastric or intestinal mucosa by their anterior parts as far as the muscularis mucosa. In humans the parasites do not reach the adult stage and die off spontaneously after 3 weeks. The clinical consequences are identical in the various genera. Abdominal pain and nausea may occur within a few hours after eating infected fish or cephalopod, but symptoms may have a late onset, and appear up to three weeks later. Sometimes the worm is regurgitated. Pyloric stenosis has been described. The infection is sometimes confused initially with appendicitis, stomach ulcer, duodenal ulcer, stomach cancer or Crohn’s disease. Rarely the worms perforate the intestinal wall and are found in the peritoneum. Eosinophilia is present. Therapy consists of mechanical removal by means of surgery or endoscopic extraction. Approximately 95% of all cases in the world, which amounts to some 2000 cases annually, occur in Japan. Many different species of Anisakis larvae are being recognised as the cause of hypersensitivity reactions after eating fish. The worm can in fact trigger quite dramatic hypersensitivity reactions, even after it is dead. The antigens are apparently both heat-stable and cold-stable. This kind of reaction is quite unusual for worms, although worm infestations are often accompanied by a hyper-IgE response. [Similar problems may be caused by leakage from an Echinococcus granulosus cyst]. The first signs of an allergic reaction usually occur 60-120 minutes after ingestion, but may be delayed for up to 6 hours later, probably due to passage of the food bolus through the gastro-intestinal tract. This means that urticaria and angio-oedema may occur at night. The diagnosis of allergy to Anisakis simplex is based on (1) a compatible anamnesis such as urticaria or angio-oedema after consumption of saltwater fish, (2) a positive skin prick test, (3) specific IgE against Anisakis simplex via radio-immunoassay, (4) negative reactions to the proteins of fish. There are, however, people who have antibodies to Anisakis without ever having exhibited symptoms. According to the guidelines of the European Community fish must be visually inspected and parasites removed, and heavily infested fish must be destroyed. Species which are marinated or salted at temperatures below 60°C should be stored for 24 hours at –20°C. In the USA fish which is not cooked or processed above 60°C, should be frozen at –35°C for at least 15 hours or at –23°C for at least 7 days.

These nematodes belong to the Ascarididae. They are parasites of carnivores and rodents. Baylisascaris procyonis is an intestinal parasite of raccoons (Procyon lotor). These animals have the habit of always defecating in the same place. These "latrines" are visited by various rodents and birds, which promotes transmission. Small mammals are the intermediate host. Baylisascaris transfuga infects bears. Infection is caused by accidental ingestion of an egg. The worm can provoke retinitis and eosinophilic meningo-encephalitis (visceral larva migrans). Neurological symptoms are prominent in infections with Baylisascaris sp. Eosinophilic pseudotumours in the heart have also been described.

Synonyms for Capillaria hepatica are Hepaticola hepatica and Calodium hepaticum. These nematodes belong to the Trichuridae. They normally infect the liver of rabbits and rodents such as rats and mice. The parasite can be found occasionally in other mammals. Adult worms are 20 mm long. The parasitosis is rarely observed in humans. During the life of the host, eggs are only found in the liver and they do not enter the intestinal lumen. The parasites die after 1 to 4 months. Predation, cannibalism and scavenging play a large part in the life cycle of this worm. Adults lay eggs in the liver of the final host. Eggs of C. hepatica are not, or only minimally, embryonated in the liver. If after the death of the host the liver decomposes on the ground, eggs do not survive the rotting process for long. If the liver of the first host is eaten by another animal the eggs develop further and somewhat later are eliminated with the faeces of this last animal. In the intermediate host the eggs only pass through the intestine, with intraluminal maturation of the eggs. After embryonated eggs land on the ground they mature further. Eggs of C. hepatica are also found in earth worms. This "transport host" may facilitate the infection of another animal. If they are eaten by a human or a rodent, larvae will be released from these eggs and migrate to the liver where they become adult in 2-3 weeks. Egg laying follows. People become infected by eating contaminated food or drinking soiled water. Infection is not caused by eating infected liver. The symptoms are those of visceral larva migrans, with hepatomegaly, eosinophilia and/or a liver abscess. The diagnosis is made via liver biopsy, not via finding eggs in faeces. The eggs are morphologically similar to those of Trichuris trichiura. Observation of eggs of C. hepatica in human faeces only indicates passage eggs (spurious infection). Hepatic capillariasis may be treated with albendazole.

The nematode Cheilobus quadrilabiatus belongs to the Rhabditidae and is very probably a pseudoparasite. Authentic infections in humans are questionable.

Nematodes of the genus Cheilospirura belong to the Acuariidae. A case of infection with such a parasite has been described in the Philippines. Not enough is known about these worms. C. spinosa is found in the crop of certain birds. Locusts are thought to be intermediate hosts.

These nematodes belong to the Dioctophymatidae. This family has three genera: Dioctowittius, Mirandonema and Dioctophyma. Each genus of these nematodes has only one species. The last mentioned has been found in a number of mammals and in humans. Probably any large mammal can act as host. Fish-eating mammals are at increased risk. Horses, cattle and pigs may become infected when they accidentally swallow an infected oligochaete. As prevention, water should be boiled and fish well cooked through. Dioctophyma renale is a real giant worm. The males are 20 cm long and 6 mm broad. The female worms are up to 100 cm long and 12 mm wide. They are blood red and have blunt extremities. The eggs have thick shells and should stay in water for 2-12 weeks in order to embryonate (the time depends on the temperature). After emerging from the egg, the larva is eaten by an aquatic oligochaete annelid Lumbriculus variegatus. The larva penetrates the ventral blood vessel, where it develops further. If the infected annelid is swallowed accidentally, the larva is released and will migrate to the kidney of the host and there develop into an adult worm. If the annelid is consumed by a fish or a frog, these latter animals become paratenic hosts. If such a paratenic host is eaten by a human, the larva penetrates the mucosa and submucosa of the stomach. After five days the parasite migrates to the liver. It stays in the liver parenchyma for approximately 50 days. It then migrates to the kidney, usually the right kidney. The eggs pass to the outside world via the urine. The immature worm can also be found beneath the skin. The growing worm produces necrosis so that the increasing internal pressure reduces the thickness of the kidney wall. Should the worm break through the renal capsule, the parasite may get into the peritoneum. Therapy is surgical.

The nematode Diploscapter coronata belongs to the Rhabditidae and is very probably a pseudoparasite. Authentic infections in humans are questionable.

The nematode E. aerophilus belongs to the Trichuridae. Earthworms are the intermediate host. The final host of Eocoleus aerophilus (synonym Capillaria aerophila) is the fox, although other carnivores such as cats and dogs can also become infected. Sometimes the parasite is found in hedgehogs. This worm can also infect humans. The adult parasite is found in the mucosa of the respiratory system. Its distribution is cosmopolitan. Under optimum conditions the eggs become infectious in 35-45 days. In foxes the parasite survives for approximately ten to eleven months.

Nematodes of the genus Eustrongylides belong to the Dioctophymatidae. There are eleven species in the genus. The larvae are bright red, 25-150 mm long and 2 mm in diameter. They infect freshwater, brackish-water and saltwater species of fish. They have fish-eating wading birds such as herons and flamingos as their final hosts. The adult parasites cause large swellings in the proventriculus of these animals. They only live a few weeks, however. During this brief period they produce eggs which embryonate in the water. These hatch in aquatic oligochaetes where they will develop in the ventral blood vessel. Fish which eat these oligochaetes become paratenic hosts. The birds then become infected by eating infected fish. The large larvae can easily be seen with the naked eye so that infected fish are not very appetising, which explains the rarity of human cases. When infected fish is eaten raw or insufficiently cooked, the worms may attach to the intestinal wall. They penetrate the wall and cause a perforation, resulting in peritonitis and possibly abscess formation. Eosinophilia may occur. Treatment consists of mechanical removal by means of surgery or endoscopy. There is a high risk of septicaemia.

Nematodes of the genus Gnathostoma belong to the Gnathostomatidae. Various species may cause severe infections in humans: G. doloresi, G. hispidum, G. spinigerum, G. nipponicum. These infections are not uncommon in the Far East and Southeast Asia, but also occur in the New World. The male worms are 10-25 mm long and the females measure 25-55 mm. They have a characteristic row of hooks around the anterior part. The final host for G. hispidum is the pig. The usual final hosts for G. spinigerum are dogs and cats. In these animals G. spinigerum forms a tumourous mass in the stomach wall. The eggs reach the outside world in the faeces. If they are dropped into water they will hatch 10 days later. Freshwater copepods (Cyclops) are the first intermediate hosts. Fish, amphibians and various mammals may become infected by eating the infected Cyclops. There is low host-specificity and humans can also become infected. Humans usually become infected by eating an infected fish or other transport host (chicken, frog or snake). The larvae cannot develop to adult worms in humans. They migrate through the body, and in doing so may trigger itching, painless, transient subcutaneous swellings. These symptoms occur after an interval of days to weeks, and they may be similar to cutaneous larva migrans caused by animal hookworms. The swellings are caused by local oedema, necrosis and haemorrhages within the migration path. If the larvae penetrate vital organs (e.g. the brain) the swelling may be life-threatening. Gnathostomiasis is an important cause of eosinophilic meningitis and myelitis. The larva can penetrate the eye resulting in haemorrhages, detached retina and blindness. The infection may resemble toxocariosis, Loa loa infection, sparganosis, fasciolasis, paragonomiasis or trichinellosis. Angiostrongylus cantonensis is another parasite which can cause eosinophilic meningitis. The treatment is symptomatic and if necessary surgical. Albendazole 400 - 800 mg daily for 21 days is recommended.

The nematode Gongylonema pulchrum belongs to the Gongylonematidae. G. pulchrum develops in the haemocoel and the muscles of a large number of species of coprophagous beetles (e.g. dung beetles) and cockroaches. As an adult parasite it lives in the mucosa and submucosa of the foremost part of the intestine of birds and mammals, such as cattle, sheep, goats, camels, deer, rabbits, bears, pigs and horses. The cuticula in adult worms is covered with thick wart-like nodules. In humans the parasite causes ulcers of the tongue, mouth, cheeks, gums or lips. Treatment consists of surgical extraction.

The nematode Haemonchus contortus belongs to the Trichostrongylidae. This nematode usually parasitises ungulates such as cattle, sheep, goats and deer. The worm sucks blood and lives in the abomasum (stomach). The infectious larvae are quite resistant to drying out and cold. Only a few cases of infection in humans are known. Transmission is by swallowing third-stage larvae.

For Halicephalobus gingivalis, see Micronema deletrix.

This nematode belongs to the Robertdollfusidae. It is an intramuscular parasite of humans. It has been described in a patient in Tasmania. Adult male and female worms, and also larvae, were found during muscle biopsy of the lateral thigh muscle. There were signs of polymyositis. H. perplexum is differentiated from all other genera of the Muspiceoidea by the presence of a number of well-defined morphological features. The parasite must be differentiated from Trichinella spiralis larvae, from coenurosis and from muscle sarcocystosis.

The nematode Lagochilascaris minor belongs to the Ascarididae and is closely related to Toxocara and Toxascaris. The name refers to the typical split lips (Gr. lagos = hare; cheilos = lip). Opossums are natural hosts. Rodents may be paratenic hosts. Infections occur in South America. Lagochilascaris minor can provoke chronic swellings and purulent abscesses in the neck, ear, mastoid, eye and retropharyngeal space in humans. Neck abscesses may resemble scrofulosis (tuberculosis). Infections may persist for years. Fatal encephalopathy may result from the presence of the worms in the central nervous system. A few cases have been known in which treatment with ivermectin was effective. Thiabendazole has also been found to be curative.

Mammomonogamus laryngeus and M. nasicola are nematodes which rarely infect humans. Infection is known as human syngamosis. This term refers to the taxonomic family of the worms, the Syngamidae. The normal hosts are ungulates (cattle, sheep, goats, deer), but also felines and elephants can be infected. Several cases have been reported from the Caribbean and Latin America. The worms are located in the respiratory tract (larynx and nose). The eggs are coughed up, swallowed and emerge with the faeces. The larvae of M. nasicola bore into earthworms, snails and maggots. Clinical symptoms in humans are chronic non-productive cough with discomfort in the throat. The parasites can be removed by endoscopy. The Y-shaped tangle of the parasites, caused by the male and female being permanently in copulation, is typical.

The nematode Marshallagia marshalli belongs to the Trichostrongylidae. Infections in humans are extremely rare.

The nematode Mecistocirrus digitatus belongs to the Trichostrongylidae. The parasite usually infects cattle. Infections in humans are very exceptional.

The nematode Mermis nigriscens belongs to the Mermithidae and is a pseudoparasite. No authentic infections in humans are known.

The nematode Metastrongylus elongatus (syn. Choerostrongylus) belongs to the Metastrongylidae. The parasite very rarely causes infections in humans. Infections with M. apri, M. pudendotectu and M. salmi are also known. These species have oligochaetes as their intermediate host (e.g. Lumbricus). Pigs and ruminants are the final hosts. They become infected by swallowing an infected earthworm. The parasites penetrate the intestinal wall and migrate to the lungs of the animal.

Micronema deletrix is possibly identical to Halicephalobus gingivalis. These nematodes belong to the Cephalobidae. This parasite infects chiefly horses, but accidental infection of humans has been described. Skin wounds are the portal of entry. In humans a very severe, even lethal eosinophilic meningo-encephalitis and myelitis may occur.

The nematode Nematodirus abnormalis belongs to the Trichostrongylidae. Infections are not unusual in cattle, but infection of humans is extremely rare.

Nematodes of the genus Ostertagia belong to the Trichostrongylidae. The name of the genus refers to Ostertag, who described the parasite in Germany in 1890. Ostertagia ostertagi and Ostertagia circumcincta (syn. Teladorsagia circumcincta) usually infect ungulates (cattle, goats, sheep, llamas, deer). They live in the abomasum. The parasites easily survive winter in regions with a temperate climate. The distribution of Ostertagia ostertagi is cosmopolitan. Infections in humans are extremely rare.

The nematode Parascaris equorum belongs to the Ascarididae. The distribution of the parasite is cosmopolitan. The usual host is the horse (chiefly foals). The eggs are round and are covered in a sticky substance with which they attach to objects in their surroundings. Embryonated eggs remain viable for several years. Humans may become infected by swallowing an egg. Infections in humans are very rare. The adult worms are found in the small intestine. They are 10-15 cm long.

The nematodes of the genus Parastrongylus belong to the Angiostrongylidae. Infections with Parastrongylus mackerrassae and P. malaysiensis have not to date been confirmed. On the other hand, infection with P. cantonensis (synonym Angiostrongylus cantonensis) does occur occasionally. The latter parasite has snails as its first intermediate host (Achatina, Pila, Veronicella). The larvae subsequently penetrate crabs, frogs, planaria or freshwater shrimps. Rats are the final host. Humans may become infected by swallowing larvae in a snail or paratenic host. Eosinophilic meningitis or myelitis will follow, with an incubation period of about 9 days. Severe headache and radicular pain are typical. The cerebrospinal fluid contains an elevated number of eosinophils. The differential diagnosis includes gnathostomiasis, neurocysticercosis and toxocariasis (visceral larva migrans). In the New World, baylisascariasis (Baylisascaris procyonis) can resemble Parastrongylus cantonensis infection. Corticosteroids (prednisolone x 2 weeks) and mebendazole or albendazole are used in treatment, although the role of antihelminthics is controversial and most cases heal spontaneously. A completely different pathology is caused by P. costaricensis (synonym Angiostrongylus costaricensis). This parasite occurs in Central America, Brazil and Peru. A land snail (Vaginulus sp.; family Veronicellidae) is the first intermediate host. The larvae can be found in the slime from the snail. In this way they get onto plants and the ground. In one study, eating raw mint and ceviche (marinated raw fish) were both risk factors for infection. Here too, rats especially the cotton rat (Sigmodon sp.) are the normal final hosts. The adult parasite is found in the mesenteric blood vessels (e.g. ileocaecal arterioles) in both the final hosts and in humans. Eosinophilic ileitis (enteritis) or appendicitis may result. Treatment is surgical. Mebendazole or thiabendazole are also given. The therapeutic role of albendazole is not yet clear.

Nematodes of the genus Pelodera belong to the Rhabditidae. They are often considered to be a subspecies of Rhabditis sp. There are four species which cause infections in mammals. Infections in dogs, horses, cattle and sheep are not unusual. In humans, dermatitis resembling cutaneous larva migrans has been described (Pelodera strongyloides). It is doubtful, however, whether the identification was correct in those cases where infections in humans have been described. P. teres is probably a pseudoparasite. It is a worm which normally lives in the open.

Nematodes of the genus Philometra belong to the Philometridae. They are probably pseudoparasites which can accidentally get into a skin wound. Philometra sp. parasitise exclusively fish (carp, pike and others). Many species have copepods as intermediate host.

Nematodes of the genus Physaloptera belong to the Physalopteridae. Physaloptera caucasica and P. transfuga are rarely found in humans. These parasites have various vertebrates as their normal host. They occur in Central Africa, Mozambique, Uganda and Malawi, although cases have been reported from India, the Middle East and also Latin America. In these cases the diagnosis was based solely on egg identification, so misdiagnosis is possible. The pathology resulting from these parasites has not yet been fully described. The worms live with their heads buried in the gastro-intestinal tract, from the oesophagus to the ileum. They probably do not suck blood, but feed on the food in the stomach or in the intestinal lumen. The life cycle of some species is unknown, but the cycle of others has been investigated. P. praeputialis occurs in cats and has crickets (Acheta assimilis) as its intermediate host. P. rara occurs in carnivores (coyote, Canis latrans) in North America and has various beetles and a cricket as its intermediate hosts. Snakes (including rattlesnakes) are paratenic hosts for the latter species.

Rhabditis sp. are nematodes which belong to the Rhabditidae. Rhabditis elongata, R. inermis and R. hominis infections are very rare in humans. Some urinary tract infections and intestinal infections have been reported from the Far East (including Thailand and China) and from Zimbabwe. The nematode is free-living, but can parasitise mammals (rodents) under various conditions. The status of both R. axei and R. niellyi is unclear. R. pellio, R. terricola and R. taurica are probably pseudoparasites. One peculiarity in certain Rhabditis species, is that the third stage larva can either develop to a fourth stage, or into a dauer larva (a larva suited to survival in unfavourable environmental circumstances), or into a parasitic, infectious larva.

Nematodes of the genus Rictularia belong to the Rictulariidae. The normal hosts are bats and rodents. Various insects and centipedes serve as intermediate hosts. The genus Rictularia contains a number of worms which only very rarely infect humans. Only one case of an infection in a human has been described. It was an adult worm in an appendix (R. pterygodermatites).

The nematode Spirocerca lupi (synonym Spirocerca sanguinolenta) belongs to the Spirocercidae. Coprophagic beetles are the intermediate hosts. Dogs, foxes, jackals, wolves and felines serve as the usual final hosts. In dogs there is transplacental transfer of larvae. In their normal host the parasites form growths in the wall of the oesophagus, stomach or aorta. In dogs they often migrate to unusual areas, with lesions of the aorta and oesophagus and even necrosis of the salivary glands. Infected dogs have an increased incidence of sarcomas. One human case has been reported, in which the adult parasites had become established in the terminal ileum.

The nematode Syphacia obvelata belongs to the Oxyuridae. This parasite infects chiefly rodents. In the past there has been confusion between this parasite and Syphacia muris. The parasites are found in the large intestine and lay their eggs peri-anally. Only one human case has been reported.

The nematode Ternidens deminutus belongs to the Chabertiidae. The parasite is related to Oesophagostomum sp. Infection is not infrequent, but only occurs in specific areas. Its distribution includes Asia and Africa, chiefly in Zimbabwe. The normal hosts are various monkeys. Infection in humans is limited to eastern and southern Africa, which suggests that possibly another, morphologically similar parasite is involved here. The taxonomy, however, is still unclear. The larvae are found in the mucosa of the colon. Adult worms are located in the colonic lumen. The method of transmission is as yet unclear. Attempts at transmission via oral inoculation and transcutaneous routes, were not successful. Possibly there is a paratenic host, perhaps an insect, which has not yet been identified.

Nematodes of the genus Thelazia belong to the Thelaziidae. They are parasites of the eye, the orbita and the lacrimal system in birds and mammals. Thelazia californiensis is found in California. T. callipaeda is found in Asia. Larvae are ingested by flies (Musca sp. and others) which feed on tears and eye secretions. In the insect the worm develops further, the speed of which is determined by the ambient temperature. The average time is two weeks at 25° C. When the fly feeds again, the infectious larva penetrates the final host. After approximately a month it becomes an adult. In humans, parasites such as T. californiensis and T. callipaeda may cause chronic unilateral conjunctivitis. A swift recovery can be expected after mechanical removal.

Nematodes of the genus Toxocara belong to the Ascarididae. Toxocara canis and T. cati (synonym Toxocara mystax) are parasites which can cause a visceral larva migrans syndrome, with or without asthma. If they reach the retina, they may lead to chorioretinitis with blindness as a possible outcome. Infection occurs by swallowing an egg that has reached the outside world via the faeces of a dog (T. canis) or a cat (T. cati). No human infections with T. pteropodis and T. vitulorum have as yet been identified. In the dog, the further development of T. canis is determined partly by the age and sex of the animal. In young puppies the larvae first migrate to the lungs, and then return to the intestine via the trachea. In older animals somatic migration is more common, including transplacental migration to the foetus. Prenatal infection is more important in these animals than transmammary infection. There is no evidence to assume a similar course in T. cati. A Toxocara parasite may become adult and eggs may appear in the faeces of humans in exceptional circumstances (e.g. HIV infection). Treatment is based on steroids and albendazole or diethylcarbamazepine (DEC). Nevertheless the effect of the anthelmintic on the extra-intestinal larvae is limited. Intra-ocular infection resulting from Toxocara larvae may lead to traction upon the retina resulting in retinal detachment. Vitreoretinal surgery has a good chance of leading to an improvement in vision in approximately 50% of cases.

Nematodes of the genus Trichostrongylus belong to the Trichostrongylidae. Infection of humans by Trichostrongylus colubriformis (synonym T. instabilis) is not unusual, unlike infection by T. affinis, T. axei, T. brevis, T. calcaratus, T. capricola, T. lerouxi, T. orientalis, T. probolurus, T. skrjabini and T. vitrinus. These are small red worms which have a cosmopolitan distribution and infect birds, ruminants, rabbits and rodents. T. probolurus parasitises a gazelle and camels. T. colubriformis normally parasitises the small intestine of sheep and goats. In some regions (Iran, Central Africa, Egypt, Java, India) humans in rural areas are frequently infected. Adult worms are approximately 5 mm long. Fertilised female worms produce quite large eggs (85 x 115 µm). These are rather longer and more pointed than the eggs of Ascaris. They contain a morula. Once outside the body the eggs hatch. At an ambient temperature of 22°C the rhabditiform larva takes 6 days to change into an infectious filariform larva. The infectious larvae of T. colubriformis are found on ground vegetation and are resistant to drying out. They can be differentiated from hookworm larvae and Strongyloides larvae by the typical small nodule at the tail. The larvae can penetrate the skin, but faeco-oral transmission is also possible. The parasites penetrate the intestinal mucosa and subsequently migrate back to the intestinal lumen. Most infections are asymptomatic. It is important, however, to differentiate between infections by hookworms or by Strongyloides stercoralis. Albendazole is active against these worms.

Data concerning the nematode Trichuris vulpis are unclear.

The nematode Turbatrix aceti belongs to the Cephalobidae. This is a pseudoparasite which can accidentally be brought into the vagina during douching.

Bertiella studeri belongs to the Anoplocephalidae. It is a cestode (tapeworm) which normally parasitises monkeys of the Old World. Infections in humans occur regularly, chiefly in Southeast Asia and the Philippines. The scolex is not armoured and the proglottids are much broader than they are long. The egg is characteristic and measures 40-50 µm in diameter. Mature proglottids are eliminated in chains of approximately 12 segments. As with many Anoplocephalidae, various mites are intermediate hosts (Scheloribates sp.; Oribatidae). Accidental ingestion of such infected mites completes the life cycle. These mites are also the intermediate host for Moniezia sp. (the tapeworms of ungulates such as sheep, cattle and goats). B. mucronata is similar to B. studeri. This parasite can also infect humans. B. mucronata is a parasite of monkeys in the New World. Children may become infected, for example by a monkey kept as a pet. The symptoms are minor or the infection may be completely asymptomatic. As with many cestodes the parasites are sensitive to praziquantel. Niclosamide is also used as treatment.

These cestodes belong to the Diphyllobothriidae (Pseudophyllidea). The genus Diphyllobothrium contains many species of tapeworms: Diphyllobothrium cameroni, D. cordatum, D. dalliae, D. dendriticum, D. elegans, D. hians, D. klebanovskii, D. lanceolatum, D. latum, D. nihonkaiense, D. orcini, D. pacificum, D. scoticum, D. stemmacephalum (syn. Diphyllobothrium yonagoensis), D. (Spirometra) houghtoni, D. (Spirometra) mansoni, D. (Spirometra) mansonoides and D. (Spirometra) theileri (synonym Spirometra pretoriensis). Probably D. (Spirometra) erinoceiuropae and D. erinacei are the same as D. (Spirometra) mansoni. Diphyllobothrium giljacicum, D. minus, S. nenzi, D. skrjabini, D. tungussicum and D. ursi are synonyms for D. dendriticum. For a number of these cestodes the first intermediate host is a copepod. Generally fish are second intermediate hosts, but the intermediate hosts for a number of worms are not yet known. The normal final host depends on the species of parasite. They include seals, sea-lions, cetaceans, cats, dogs, bears, raccoons and birds. Infection with these worms is not frequent. Previously infections with D. latum were quite common in Scandinavia, but nowadays such infections (due to eating infected freshwater fish) are unusual. There have been sporadic infections in other European countries (Italy, Switzerland, Germany, Romania) and also in the USA and Canada. Severe and long-term infection with D. latum can produce vitamin B12 deficiency, but was well known only in Finland. D. pacificum occurs in Peru. This is a worm which grows to 1 metre long. The proglottids are very short and can therefore be easily differentiated from Taenia solium or T. saginata. People become infected by eating infected seafish. Seals form the natural reservoir. The number of infections with D. pacificum fluctuates widely, partly due to the north-south migrations of sea mammals under the influence of the changing seawater temperatures and the influence of El Niño upon fish stocks. Patients sometimes report episodes of meteorism and of spontaneous elimination of the whole worm (in up to 25% of cases). Vitamin B12 deficiency does not occur in these cases. Diphyllobothrium (Spirometra) mansonoides is a tapeworm of dogs and cats in the Western hemisphere (New World). The eggs are similar to those of Diphyllobothrium latum. They are somewhat smaller, however (57-66 µm x 33-37), are ellipsoidal and have a conical, rather prominent operculum. A nodular thickening can often be observed at the opposite pole from the operculum. The eggs are not embryonated when they are eliminated with the faeces. In infections, one needs to distinguish between the presence of larvae and an adult worm in the human body. When an individual is infected by eating fish which contain one or more plerocercoid larvae, there is further development of the parasite to an adult worm. The adult worm is found in the lumen of the small intestine. When infection by Diphyllobothrium (Spirometra) mansonoides occurs due to drinking water containing infected copepods, the parasite may develop as a plerocercoid larva in the tissues, e.g. in an eye. This disorder is known as sparganosis. The infection may also result from placing infected frog meat or snake tissue on the skin, which is sometimes done in traditional Eastern medicine. Eating insufficiently heated meat from frogs, snakes, chickens, ducks and pigs can give rise to sparganosis. Diphyllobothrium (Spirometra) mansonoides is responsible for human cases of sparganosis in the West. Other Diphyllobothrium (Spirometra) species are responsible for sparganosis in other parts of the world. The plerocercoids of Diphyllobothrium (Spirometra) mansonoides secrete a substance which has an effect similar to that of the growth hormone of various mammals. This substance is very similar to human growth hormone. Its role in the worm is unclear. As with many cestodes, the parasite is sensitive to praziquantel.

These cestodes belong to the Diphyllobothriidae. Diplogonoporus balaenopterae (synonym Diplogonoporus grandis) is a tapeworm of cetaceans. Dogs can also become infected. Infections with this parasite occur regularly in Japan. This is probably connected to the frequent consumption of raw saltwater fish and whale meat. Copepods are the first intermediate hosts. Saltwater fish are the second intermediate hosts. People become infected by eating infected fish. The final host of D. brauni is not yet known with certainty. Possibly it is a fish-eating species of bird. Little is known as yet about D. fukuokaensis, but humans can become infected. The adult worm is found in the lumen of the small intestine. It grows to several metres long. The scolex on the other hand, is only one millimetre in length. As with many cestodes the parasite is sensitive to praziquantel.

These cestodes belong to the Dipylididae. Dipylidium caninum is a tapeworm with cosmopolitan distribution (except for Australia). The adult worm remains in the lumen of the small intestine. Cats, dogs and other Carnivora are the final hosts. Proglottids may creep about actively near the dog’s anus. Fleas (Ctenocephalides, Pulex) and the larvae of dog lice (Trichodectes canis) are intermediate hosts. The adult worm measures 15-40 cm and has a delicately armoured conical rostellum on the scolex. People become infected by accidentally swallowing a flea containing cysticercoids. The course of infection is almost always asymptomatic. The diagnosis is made by detecting typical egg clusters in faeces. One such small packet will contain 8 to 13 eggs. As with many cestodes the parasite is sensitive to praziquantel. As prevention it is advisable to de-worm dogs regularly and to eradicate ectoparasites.

These cestodes belong to the Hymenolepididae. Drepanidotaenia lanceolata is a tapeworm with cosmopolitan distribution. The adult parasite probably lives in the lumen of the small intestine. Copepods (Cyclops, Diaptomus) are intermediate hosts. The usual final hosts are birds. People become infected by swallowing an infected copepod. Symptoms are either minor or the infection is completely asymptomatic.

These cestodes belong to the Hymenolepididae. Hymenolepis diminuta is a tapeworm with cosmopolitan distribution. The adult parasite is found in the lumen of the small intestine. It is quite small for a tapeworm (2-6 cm), which is where its specific name comes from. The tapeworm is not armoured. Rodents (rats) are the normal final hosts. Various arthropods, including insects such as fleas are the intermediate hosts. If they are accidentally swallowed by a human, infection follows. Most infections are without symptoms. As with many cestodes the parasite is sensitive to praziquantel.

These cestodes belong to the Hymenolepididae. Hymenolepis nana (synonym Vampirolepis nana) occurs in foci and has a cosmopolitan distribution. The highest prevalence of this cestode is found in hot, dry regions. People become infected by swallowing an egg (faeco-oral transmission) or by accidentally swallowing an insect (flea, weevil) which acts as intermediate host. An intermediate host is not essential for infection. Humans are the only definitive host. The adult worm is found in the lumen of the small intestine. The adult parasite is smaller than H. diminuta: it only measures 2-4 cm (dwarf tapeworm). The strobila contains 100 to 200 proglottids. The course of infection is almost always asymptomatic. The treatment of choice is praziquantel.

These cestodes belong to the Anoplocephalidae. Inermicapsifer madagascariensis (synonym Raillietina madagascariensis) normally parasitises African rodents and hyraxes, but humans may also become infected. Outside Africa humans are said to be the only definitive host for this cestode. Cases of infection with I. cubensis have been reported from South America and Cuba. The scolex is not armoured. The strobila is up to 42 cm long. The mature proglottids are rather broader than they are long. The uterus is filled with capsules, each of which contains 6 to 10 eggs. The life cycle is unknown, but probably an arthropod is the intermediate host. Most infections lead to few if any symptoms. The infection is treated with praziquantel.

These cestodes belong to the Diphyllobothriidae (Pseudophyllidea). Ligula intestinalis is a tapeworm which normally has fish-eating birds as its final host. Copepods (Cyclops) are the first intermediate host. Freshwater fish (cypriniforms) are the second intermediate host. People become infected by eating infected fish. The adult worm is found in the lumen of the small intestine. Most infections lead to few if any symptoms. Praziquantel is the logical choice for treatment, but there is little experience in view of the rarity of infections. Infections have been reported from Poland and Romania.

These cestodes belong to the Anoplocephalidae. Mathevotaenia symmetrica is a tapeworm. The adult parasite is found in the small intestine. The usual final hosts are rodents. Tribolium and Plodid insects are the intermediate hosts. People become infected by ingestion of an infected insect. This happens on occasions. Cases are known from Thailand. The parasite is known under many synonyms (Opussumia, Inversia, Morosovella, Paratriotaenia, Markewitschitaenia, Hickmania, Schizorchodes, Priodontia, Linstoparonia, Mangustella, Vasoramia). Most infections lead to few if any symptoms. Praziquantel is the logical choice for treatment, but there is little experience in view of the rarity of infections.

These cestodes belong to the Mesocestoidae. The taxonomy of this genus has been made difficult by the wide morphological variation, which is apparently host-induced. Probably, various mites are the first intermediate hosts. Several other animals can be the next intermediate host: amphibians, snakes, small mammals and also birds (M. variabilis). Dogs and cats are also intermediate hosts and one way these become infected is by eating infected birds. The habit of feeding dogs offal from birds promotes infection. Mesocestoides lineatus and M. variabilis are tapeworms which occasionally cause infection in humans. People become infected by ingesting a tetrathyridium larva in an intermediate host. Cases occurred in Japan after eating snake, and drinking fresh snake blood and turtle blood. This may appear rather bizarre, but traditionally blood from the snapping turtle is used in Japan as a tonic. The symptoms are usually mild. Praziquantel is used in treatment.

These cestodes belong to the Anoplocephalidae. The normal final hosts are cattle, sheep and goats. Galumna and Scheloribates mites are the intermediate hosts. Monieza expansa is a tapeworm which infects humans in very exceptional cases. Russia is one country where infections occur. The adult worm is found in the lumen of the small intestine. Infections are generally asymptomatic. As with many cestodes the parasite is sensitive to praziquantel. Albendazole is possibly also active against the worm.

These cestodes belong to the Taeniidae. Multiceps multiceps (synonym Taenia multiceps), M. brauni (synonym T. brauni), M. glomeratus (synonym T. glomeratus), M. longihamatus (synonym T. longihamatus) and M. serialis (synonym T. serialis) are tapeworms which may occasionally infect humans. Ungulates are intermediate hosts of M. multiceps and canines the final hosts. For M. serialis rodents and lagomorphs (rabbits, hares) are intermediate hosts and various carnivores are the normal final hosts. M. brauni has rodents as its intermediate hosts and carnivores as its final hosts. M. glomeratus has rodents as its intermediate hosts, but the normal final host is not known. When a human accidentally swallows an egg of M. multiceps or M. brauni, the larva may develop into a coenurus larva. Localisation in the eye and the brain may occur in M. multiceps and M. brauni. These worms are responsible for the most serious pathology. A visceral larva migrans syndrome may result. M. serialis may cause cysts in the tissues. M. glomeratus may become established in the muscles. M. longihamatus occurs as an adult worm in the lumen of the small intestine. As with many cestodes, the parasites are sensitive to praziquantel. Treatment of coenurosis is surgical.

The cestode Nybelinia surmenicola (syn. Aspidorhynchus, Congeria, Acoleorhynchus, Rufferia) is probably a pseudoparasite when it attaches by chance to the tonsil). It belongs to the Tentaculariidae. The adult parasite has hooks.

These cestodes belong to the Diphyllobothriidae. Pyramicocephalus anthocephalus is a tapeworm which usually infects dogs and fish-eating mammals in the far north (Alaska, Greenland). Saltwater fish are the intermediate hosts, but very little else is known about this parasite.

Cestodes of the genus Raillietina (synonym Davainea) belong to the Davaineidae. The following species have been described in humans: R. siriraji, R. asiatica, R. garrisoni, R. celebensis and R. demerariensis. Other species have not as yet been well defined. Representatives of this genus are easily recognised by the large rostellum with hundreds of small hooks, and by the small suckers. Raillietina siriraji is a rare parasite, identified from children in Bangkok. R. celebensis occurs in the Far East (China, Taiwan, Japan) and also in Tahiti and Australia. An adult R. celebensis is approximately 16-50 cm long. The strobila contains up to 700 proglottids. The life cycle is still unclear, but probably various insects are the intermediate hosts. The reason for assuming this, is that the related R. cesticillus (a cestode of poultry) has various dung beetles and weevils, as well as Musca domestica (the house fly) as intermediate hosts. The epidemiology corresponds to that of Hymenolepis diminuta. The intermediate host of R. demerariensis is the cockroach. R. demerariensis occurs frequently in specific sites in Cuba, Ecuador and Guyana. The usual final hosts of R. celebensis are various rodents (Rattus, Mus). The intermediate host of this tapeworm is probably a species of ant within the Cardiocondyle genus. Ants are said to carry the fertilised proglottids to their nests, and to use them as food for their larvae. The oncospheres grow in these immature insects and become cysticercoids in the adult ant. Humans become infected by accidentally swallowing an ant. Generally infection does not lead to many symptoms. Sometimes white, motile proglottids are observed in the faeces. As with many cestodes these parasites are sensitive to praziquantel.

These cestodes belong to the Diphyllobothriidae. Schistocephalus solidus is a tapeworm which is found in Alaska. The adult worm is found in the lumen of the small intestine. Normally dogs and fish-eating birds are the final hosts. The first intermediate host is a copepod (Cyclops). The second intermediate hosts are freshwater fish. Infection is usually accompanied by few symptoms. Praziquantel is the logical choice of treatment, but there has been little experience with these infections.

For Spirometra sp., see: Diphyllobothrium sp.

Cestodes of the genus Taenia belong to the Taeniidae. In tapeworm infections one must distinguish between the presence of an adult worm in the intestine, and the presence of larvae in the tissues. Both may be present simultaneously. T. saginata (cattle tapeworm) and T. solium (pig tapeworm) have been discussed elsewhere. T. asiatica is possibly a subspecies of T. saginata which has adapted to pigs. This parasite occurs in Asia. The adult worm is found in the lumen of the human small intestine. Taenia crassiceps is a cestode which very rarely causes infection in humans. It can cause cysticerci in the eye. Carnivores are the normal final hosts. Rodents are the intermediate hosts. T. taeniaeformis may cause cysts in the human liver. Cats, dogs and weasels are the normal final hosts. Rodents are intermediate hosts. People become infected with this parasite by accidentally swallowing an egg. Praziquantel is used in treatment. Surgery may need to be considered.

These trematodes belong to the Achillurbainiidae. They are very similar to Poikilorchis or may possibly be the same. Achillurbainia nouveli and A. recondita are parasites which have leopards (Panthera pardus) and opossums (Didelphis sp.) respectively as their final host. Achillurbainia nouveli was found in a retro-auricular abscess in China. Crabs of the genus Paratelphusa are intermediate hosts. A. recondita produces abortive infections in humans and has been found in the omentum and in other places in the peritoneum. These infections have been reported from the USA, Honduras and Brazil. There is not sufficient experience with these infections, to be able to draw up therapeutic guidelines. Surgery is important. Praziquantel is probably a good choice, in view of its activity against many other trematodes.

This trematode belongs to the Diplostomatidae. The life cycle of Alaria americana includes snails (Helisoma) and amphibians. People can become infected by eating frogs, and probably also by eating wild duck. Alaria marcianae has a similar cycle and is regarded by some as synonymous. Planorbis snails are probably the first intermediate hosts. Amphibians and snakes may become infected. Various carnivores including cats and dogs are the final hosts. Transmammary transmission has been demonstrated in various animals, including monkeys. The term amphiparatenic host was originally used for hosts of A. marcianae. This refers to the fact that adult animals can be paratenic hosts, while juvenile animals are definitive hosts. This was demonstrated in a cat model. Pregnant and lactating animals can thus be a reservoir and a source of infection for the young animals. The parasite can cause subcutaneous nodules in humans. These should be surgically removed. Intra-ocular mesocercariae may cause blindness. Cases have been known of fatal systemic, disseminated infections with A. americana, in which lesions were found in almost all organs.

This trematode belongs to the Heterophyidae. This parasite occurs in Canada. Apophallus donicus has a snail (Flumenicola) as first intermediate host. Various freshwater fish are intermediate hosts. The adult worm parasitises cats, dogs, rabbits, foxes and birds. People become infected by eating infected fish. There is little experience as regards the treatment of such infections, but praziquantel seems a logical choice.

These trematodes belong to the Echinostomatidae. Artyfechinostomum mehrai causes infection in humans very exceptionally. The normal hosts are rats and pigs. Artyfechinostomum malayanum is a parasite which occurs in Southeast Asia including the Philippines. Transmission is due to eating insufficiently cooked freshwater snails (Bullastra cumingiana). The clinical picture is not yet fully known, but intestinal perforations may occur.

This trematode belongs to the Microphallidae. Carneophallus brevicaeca (synonym Spelotrema brevicaeca) is a parasite which occasionally infects humans. Cases have been reported from the Philippines. The worm can be found in the intestine, but ectopic location in various tissues may also occur. Primates and fish-eating birds are final hosts. Arthropods, such as crabs and decapods are intermediate hosts. People become infected by eating infected shrimp (Macrobrachium sp.). Little is known about the optimum treatment of infection with this parasite, but praziquantel seems a logical choice.

This trematode belongs to the Cathaemasiidae. Cathaemasia cabrerai was first discovered in 1984 in the Philippines (found in human faeces). Possibly, in the original description, this parasite was mistaken for Echinostoma malayanum, which was morphologically abnormal, due to praziquantel therapy. Little is known about this parasite. Probably praziquantel is active against this worm.

These trematodes belong to the Heterophyidae. Centrocestus caninus, C. cuspidatus, C. longus, C. kurokawai and C. formosanus are of minor medical importance. They occur in Southeast Asia and elsewhere, and are moderately common in Thailand. Only experimental infections are known for C. armatus. Freshwater fish are the intermediate hosts. The adult worms are found in the lumen of the small intestine. The pathology caused by these parasites is not very pronounced: vague abdominal pain to diarrhoea. The infection is usually self-limiting due to the short life-span of the parasites. Praziquantel is probably a good choice for treatment, but there is limited experience of its use.

The trematode Clinostomum complanatum belongs to the Clinostomatidae. It usually infects fish-eating water birds, but occasionally infections have occurred in humans. Cases have been described in Korea and Japan. Snails of the genera Helisoma and Lymnaea are the first intermediate hosts. Freshwater fish are the second intermediate hosts. People become infected with C. complanatum by eating fish infected with metacercariae. The worms attach to the pharynx. This causes pain. Mechanical extraction of the worm solves the problem. Compare with the clinical presentation of throat pain caused by Linguatula serrata, halzoun and with human syngamosis (infection with Mammomonogamus sp.).

For the trematode Clonorchis sinensis: see Opisthorchis sp.

The trematode Cryptocotyle lingua belongs to the Heterophyidae. The parasite occurs in Greenland and Canada. It has also been reported from other countries, where it infects foxes and other animals. Tautogolabrus and Littorina snails are the first intermediate hosts. Subsequently various seafish can become infected. Dogs, cats, birds and fish-eating mammals such as sea-lions, are the normal final hosts. It is possible that two similar parasites are classified under this name. The eggs are found in faeces.

These trematodes belong to the Dicrocoeliidae. Dicrocoelium dendriticum and D. hospes are parasites which use snails first (including Achatina or Limicolaria sp.) and then various species of ants as intermediate hosts. Sheep and ruminants are the final hosts for D. dendriticum. Infections in humans occasionally occur. The distribution of this worm is cosmopolitan. D. hospes is confined to Africa. Sometimes the eggs can be found in faeces when the person in question has recently eaten infected liver. In this case no actual infection occurs. A true infection may follow accidental swallowing of an infected ant. The adult worms are found in the bile ducts. In a severe infection obstruction may occur, with or without cholangitis. Praziquantel is used to treat.

These trematodes belong to the Heterophyidae. Little is known about them. People can become infected with Diorchitrema amplicaecale, D. formosanim or D. pseudocirratum by eating fish containing metacercariae (e.g. in Japanese sushi or sashimi).

The trematode Diplostomum spathaceum belongs to the Diplostomatidae. Snails (Lymnaea) and freshwater fish are intermediate hosts. The parasite causes significant morbidity and mortality in numerous species of freshwater fish in Europe and North America. The metacercariae affect the eyes (hence the name "eye fluke") and other parts of these animals. The adult parasite normally infects fish-eating birds, including sea-gulls. It is located in the intestines. The cercariae may actively penetrate through human skin and migrate to the eye. Little is known about treatment of infection in humans.

These trematodes belong to the Echinostomatidae. Cats, dogs, rats and herons are final hosts for some species of this genus. Snails (including Parafossarulus sp.) are the first intermediate hosts. Echinochasmus japonicus, E. cinetorchis, E. liliputanus, E. fujianensis, E. angustitestis, E. perfoliatus and E. jiufoensis are worms which regularly cause infections in humans. They are found in the Far East (China, Korea). The transmission of E. japonicus and E. perfoliatus is via ingestion of freshwater fish infected with metacercariae. People can become infected with E. liliputanus cercariae by drinking unboiled water. The adult worm is found in the intestine. The symptoms are aspecific abdominal discomfort, a feeling of distension and anorexia. Although the effectiveness of mebendazole is lower than that of praziquantel, the former still has a high success percentage (negativation of eggs in faeces in 70-85%). Pyquiton has been used for therapy with good results.

The trematode Echinoparyphium recurvatum belongs to the Echinostomatidae. These parasites have a life cycle which includes snails (Lymnaea, Planorbis, Radix, Acroloxus) and subsequently tadpoles, frogs, snails or bivalves may be infected. Various birds are the final hosts, but rats may also become infected. The parasite is found in Asia, Europe, Africa and America. Echinoparyphium recurvatum has an antagonistic effect on Schistosoma haematobium in Bulinus truncates snails. The parasite was studied in the past in order to make use of this phenomenon to combat bilharziosis. It was not used in practice, however.

These trematodes belong to the Echinostomatidae. Species belonging to the genus Echinostoma are often found in Southeast Asia. These are quite small organisms which as adult parasites are found in the intestinal lumen. Echinostoma hortense, E. malayanum, E. cinetorchis, E. echinatum (synonym E. lindoense), E. ilocanum, E. macrorchis, E. revolutum and E. japonicus are intestinal trematodes. E. jassyense is also known as E. melis. They are mainly found in Asia. People become infected (depending on the species) via eating infected frogs, snails containing metacercariae or infected fish. The adult worms are found in the lumen of the small intestine. They may sometimes cause intestinal ulcers. Echinostomatosis is often asymptomatic or accompanied by minor abdominal discomfort. Praziquantel is the treatment of choice.

The trematode Episthmium caninum belongs to the Echinostomatidae. Eggs from this parasite have been found in the faeces of a patient in Thailand. Little is known about this organism and the clinical consequences of infection. The snail which is assumed to be the first intermediate host, has not yet been identified. Fish are the intermediate hosts and they transmit the infection to humans. Birds are the usual final hosts, mammals are rarely infected.

The trematode Eurytrema pancreaticum belongs to the Dicrocoeliidae. The first intermediate host is a land snail (Bradybaena). Infection with this parasite may result from eating a grasshopper infected with metacercariae. There are various final hosts, but chiefly sheep and cattle are infected. The adult worm is found in the pancreas, in the Wirsung duct. It is approximately 1 cm long.

The trematode Fasciolopsis buski belongs to the Fasciolidae. Infections occur frequently in a few specific geographical areas of India, Bangladesh, Southeast Asia, China and Taiwan. The adult worm is approximately 3 cm long (sometimes as large as 7.5 cm) and is thus the largest trematode which infects humans. The adult worm is found in the lumen of the small intestine. The worm’s first intermediate hosts are snails belonging to the genera Hippeutis, Segmentina and Gyraulus. People become infected by swallowing water plants on which there are metacercariae (e.g. Trapa natans and related species, Eliocharis tuberosa, Eichhornia crassipes). The usual final hosts are pigs. Dogs may also become infected, but are less important in transmission. In humans infection is usually asymptomatic. Severe infections result in vague abdominal discomfort, anorexia, diarrhoea and signs of malabsorption. Sometimes significant amounts of protein may be lost via the intestine, resulting in oedema and cachexia. The worms are sensitive to praziquantel. Generally there is spontaneous recovery after 6 months.

For trematodes of the genus Fibricola, see: Neodiplostomum seoulensis.

The trematode Gastrodiscoides hominis belongs to the Paramphistomatidae. Infections are not unusual. Gastrodiscoides hominis occurs in India (Assam), Southeast Asia, the Philippines and the former Soviet Union. The parasite is conical and coloured pink. People become infect by eating infected plants. The life cycle is not fully known, but is probably similar to that of Fasciolopsis buski, with snails and water plants are actually infected. The snail Helicorbis coenosus can be infected experimentally. The worm infects pigs, cattle, primates and rodents. The adult worms are found in the small intestine and colon (caecum). Adult worms are 5-8 mm long and 5-14 mm wide at the ventral sucker. They use this ventral sucker to attach to the mucosa. Most infections are asymptomatic. Severe infections are accompanied by abdominal pain and mucoid diarrhoea. The diagnosis is made from faecal analysis. Praziquantel is effective as treatment.

Gymnophalloides seoi belongs to the Gymnophallidae. It is a parasite which has birds as its final hosts, including the oyster-catcher (Haematopus ostralegus). Oysters such as Crassostrea gigas form an important intermediate host for this trematode. These animals may contain countless metacercariae. This parasitosis is an important disease for these animals. The infection is common in Shinangun, Korea. Oyster beds in Japan are also often infected. People become infected by eating raw infected oysters. Epigastralgia may result. The eggs measure 19-21 x 14-16 micrometers.

These trematodes belong to the Heterophyidae. Haplorchis yokogawai, H. taichui, H. microrchis, H. pleurolophocerca, H. vanissimus and H. pumilio are worms which usually parasitise cats and dogs. H. vanissimus has birds as its final host. H. yokogawai can infect dogs, cats, cattle, monkeys and fish-eating water birds. Depending on the parasite species Melania, Melanoides or Stenomelania snails are the first intermediate hosts. Humans become infected when they eat a fish infected with metacercariae. There is infection of the intestine, but eggs can occasionally also be found in the spinal cord and the heart.

These trematodes belong to the Heterophyidae. Heterophyes heterophyes was until recently quite common, certainly in Egypt. The adult flukes are found in the lumen of the small intestine. Snails of the genera Pironella and Cerithidea act as the first intermediate host. The subsequent intermediate hosts are various fish, including Tilapia. Cats, dogs and fish-eating mammals are the usual final hosts. People become infected by eating fish infected with metacercariae. Related trematodes are H. dispar, H. equalis, H. katsuradai, H. nocens and H. continua. Infection with this last species is much less common. Most infections are asymptomatic.

Only a few infections with the trematode Heterophyopsis continua have been reported in the medical literature (from the Far East). Praziquantel is probably active against this worm.

The trematode Himasthla muehlensi belongs to the Echinostomatidae. Molluscs (Venus sp.) are probably the intermediate hosts. Birds are usually the final hosts. To date, however, only one case of infection in a human has ever been reported.

The trematode Hypoderaeum conoideum belongs to the Echinostomatidae. It can infect humans and in the north-east of Thailand this is relatively frequent. Infections with this parasite also occur in Taiwan. The adult worms are found in the lumen of the small intestine. Snails (Lymnaea, Planorbis) are the first intermediate hosts. Snails and tadpoles are the second intermediate hosts. The final hosts are various birds (geese). People become infected by eating infected snails. Most infections are subclinical. Praziquantel is probably a good choice as treatment.

The trematode Isoparorchis hypselobagri belongs to the Isoparorchidae. It has snails of the genus Posticobia as its first intermediate host. The adult worm is found in the swim bladder of freshwater fish. e.g. catfish (Wallagu attu). It has a special haemoglobin with a noticeably high affinity for oxygen. People become infected by eating an infected fish. Infections in humans only occur occasionally. Symptoms are minor.

These trematodes belong to the Heterophyidae. Metagonimus yokogawai (synonym Heterophyes yokogawai) is a small parasite which has snails of the genera Semisulcospira and Thiara as its first intermediate host. The parasite subsequently infects cypriniform fish. Cats, dogs and fish-eating water birds are the normal final hosts. The adult worm is found in the lumen of the small intestine. Infections in humans are not unusual, but are generally asymptomatic. Infections occur in China, Taiwan, Japan, Korea, Indonesia, the Philippines and Russia (Siberia). M. minutus is a trematode which only rarely causes infection in humans. Praziquantel is the treatment of choice.

These trematodes belong to the Opisthorchidae. Metorchis albidus and M. conjunctus occur in the far north (Alaska, Greenland). M. conjunctus is known to have the snail Amnicola limosa as its first intermediate host. Various fish are subsequent intermediate hosts. Cats, dogs and fish-eating mammals are final hosts. People become infected with these small parasites by eating fish infected with metacercariae. The adult worms are found in the bile ducts. Infections are often asymptomatic, but in severe infestation there may be aspecific abdominal discomfort. Praziquantel is used in treatment.

Only a few experimental infections with the trematode Microphallus minus have been reported.

These trematodes belong to the Nanophyetidae. These parasites are also known by the synonym Troglotrema. The parasites occur in mammals which frequent the coast of the Pacific Ocean in Canada and Alaska (Nanophyetus salmincola) and in Eastern Siberia (N. schikhobalowi). N. schikhobalowi and N. salmincola have as their natural final hosts the raccoon, skunk, dog, fox, cat, opossum and fish-eating birds and mammals. The parasite is small: 2 x 0.5 mm. The eggs measure 80 x 50 micrometers. They are yellowish brown with an operculum which is difficult to see with an optical microscope. They are very similar to the eggs of the fish tapeworm Diphyllobothrium latum. After the eggs reach the outside world from the small intestine via the faeces, they hatch within 3 months. The parasites then penetrate water snails belonging to the genera Oxytrema, Goniobasi and Semisulcospira. Sporocysts, rediae and daughter rediae are produced in these molluscs. Subsequently cercariae are released and these penetrate salmonoids (e.g. salmon, trout). The parasite becomes infectious within a very short time (10 days) after entering a salmon, although it can survive for up to 5 years. This long survival time makes it possible for salmon which make an anadromous migration to be responsible for infection of land-living mammals. [Anadromous fish remain for their whole adult lives in saltwater only returning to freshwater to spawn. The parasites are able to survive the sojourn in the ocean]. If humans eat raw or insufficiently cooked fish, infection may follow. The prepatent period is 5-8 days and is followed by abdominal pain, diarrhoea and eosinophilia. The parasite itself can become infected by a bacterium: Neorickettsia helminthoeca, which is known as the Elokomin fluke fever agent. Eating raw salmon or trout may cause haemorrhagic enteritis in dogs. However this is not caused by the worm, but the bacterium. The condition is called "salmon poisoning" and is characterised by sudden fever, vomiting, diarrhoea (possibly with blood), discharge from the eyes and lymphadenopathy. Mortality may be up to 50-90%, but if the dog survives (possibly with the help of tetracyclines) it is immune. Previously it was mistakingly thought that the salmon itself was toxic for dogs.

This trematode belongs to the Diplostomatidae. The parasite was renamed from Fibricola seoulensis to Neodiplostomum seoulensis. Some cases of infection have been reported from Korea, where it was first described in 1964. The adult worm is very small: 1 to 2 mm long. It has a typically constricted body with a large anterior part and a smaller posterior part. The posterior part contains the striking testes which stain bright red with carmine stain. At the constriction is the uterus. As with most trematodes, this parasite is hermaphrodite. Snails (Hippeutis) are the first intermediate hosts. Fish are subsequent intermediate hosts. Frogs and snakes (Rhabdophis) are paratenic intermediate hosts. Rats may become infected. People become infected via metacercariae in frogs or snakes. Related parasites, as for example Fibricola cratera, can infect raccoons. Whether accidental infections with this last parasite also occur in humans, is still unclear. The adult worm is found in the intestine. Vague abdominal discomfort and flatulence may occur. Infected animals develop atrophy of the intestinal villi and hyperplasia of the crypts. These changes are reversible after therapy with praziquantel.

These trematodes belong to the Opisthorchidae. Some species of the genus Opisthorchis cause infections in humans occasionally while other species do so quite frequently. Opisthorchis guayaquilensis and O. noverca only cause sporadic infections. O. felineus (syn. O. tenuicollis) has endemic foci in water reservoirs and river deltas. It is a common parasite in Siberia. Snails of the genus Bythinia are its first intermediate host. Cypriniform fish are subsequent intermediate hosts. Normal final hosts include dogs, cats and pigs. The adult worm is found in the bile ducts. Recurrent cholangitis may occur. People become infected by eating an infected fish.

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Opisthorchis viverrini is common in humans in North Thailand. Bithynia snails are the first intermediate host. Various freshwater fish are intermediate hosts. The adult worm is found in the bile ducts where it is responsible for recurrent cholangitis, but the majority of infections are subclinical.

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Opisthorchis sinensis (previously called Clonorchis sinensis) is a very common parasite in Southeast Asia. The adult worms are found in the biliary tract or the Wirsung duct in the pancreas. The first intermediate hosts are snails (Bythinia, Assiminea, Melanoides, Parafossarulus). Subsequently cypriniform fish become infected. Cats, dogs, pigs and fish-eating carnivores are the normal final hosts. People become infected by eating infected fish. The parasitosis is a problem not only because of the direct damage to the biliary tract and the risk of pancreatitis, but also due to the risk of bile duct carcinoma (cholangiocarcinoma) for those infected. Praziquantel is the treatment of choice for this infection.

The trematode Paryphostomum sufrartyfex belongs to the Psilostomatidae. The parasite may infect humans, but almost nothing is known about this worm. The snail Digoniostoma pulchella is thought to be the intermediate host. The final hosts are dogs, pigs and rats. Probably Artyfechinostomum sufrartyfex is identical to this worm.

These trematodes belong to the Lecithodendriidae. Infection with Phaneropsolus bonnei is common in northern Thailand. High focal prevalence may be reached. The normal hosts for P. bonnei are monkeys, but bats may also be final hosts. P. spinicirrus has been found in human faeces in northern Thailand. These trematodes are found as adult worms in the small intestine. P. bonnei eggs measure 30-32 x 15-16 micrometers. They are very similar to those of Metagonimus and Heterophyes. The eggs of P. bonnei are thinner and longer than those of Prosthodendrium molenkampi. Transmission is via eating small fish which have themselves eaten infected larval odonates (dragonfly, see transmission of Prosthodendrium molenkampi). Vague abdominal discomfort may result from these infections. Praziquantel is used in treatment.

This trematode belongs to the Philophthalmidae. Only one case of infection in humans by Philophthalmus lacrymosus has been described and that was in Yugoslavia. Birds are the normal final host. The adult worm is found in the eye (conjunctiva).

These trematodes belong to the Plagiorchiidae. Plagiorchis javanensis, P. hiranasuta, P. muris and P. philippinensis rarely cause infections in humans. These parasites normally infect birds, amphibians and bats. The life cycles are not yet fully known. Humans may be infected by eating insect larvae infected with metacercariae although this is not yet firmly established. The adult worms are found in the small intestine. Infections are generally asymptomatic or accompanied by minor abdominal discomfort.

The trematode Poikilorchis congolensis belongs to the Achillurbainiidae. It is found in Central Africa (Congo), Nigeria and Sarawak. The life cycle is unknown. This parasite causes retro-auricular cysts and abscesses. The eggs which are found in the pus are similar to Paragonimus eggs, but are smaller. Treatment is surgical. It is not known whether praziquantel is of any benefit.

The trematode Procerovum calderoni belongs to the Heterophyidae. Its distribution includes China and the Philippines. Snails of the genera Melania and Thiara are the first intermediate host. Subsequently the larvae infect various fish. Dogs and cats are the natural final hosts. The adult worm is found in the lumen of the small intestine. Infections in humans are rare. People may become infected by eating fish infected with metacercariae. Although P. varium is infectious experimentally, no natural cases have been recorded.

The trematode Prohemistomum vivax belongs to the Cathycotylidae. Snails (Cleopatra, Melanopsis) are the first intermediate hosts. Freshwater fish are the second intermediate hosts. Fish-eating birds are the normal final hosts. People become infected by eating parasitised fish. Infections with this parasite are rare.

The trematode Prosthodendrium molenkampi belongs to the Lecithodendriidae. Infections occur in foci in northern Thailand and in Indonesia. The normal hosts are rats and bats. P. molenkampi eggs have a smooth shell. They reach the outside world via the faeces. After hatching the parasite infects a water snail. The cercariae which are released are in turn attacked by larval odonates (dragonflies), after which the latter become infected. These insect larvae are regarded as a delicacy in the rural areas of Southeast Asia. Eating fish which have fed on these insects can also lead to infection. Apparently there are few clinical consequences of this parasitosis.

These trematodes belong to the Opisthorchidae. The parasite is found in Russia. Very little is known about Pseudamphistomum aethiopicum. Freshwater fish are the intermediate hosts. Cats, dogs, weasels and foxes are the final hosts. Cystic nodules resulting from infection with P. aethiopicum are sometimes found in humans, in the wall of the small intestine. The first case in humans of infection with P. truncatum was described in 1982. The adult trematode is found in the liver. People become infected by eating parasitised fish.

There are no reliable data concerning human infections with the trematode Psilorchis hominis.

The trematode Pygidiopsis summa belongs to the Heterophyidae. Infection of humans is exceptional. A few infections have been reported from Korea. Fish which live in brackish water are the intermediate hosts of this trematode. The parasite then infects fish-eating birds which become carriers of metacercariae. The adult worm is found in humans in the lumen of the small intestine. The number of adult worms may be quite high: up to thousands in one person. The parasite is very small: 0.52 – 0.82 mm and 0.31-0.39 mm broad. The body becomes narrower at the front and is blunt at the rear. The eggs are smaller than those of Metagonimus or Heterophyes. They only measure 19-24 x 11-13 micrometers. Praziquantel is probably active against this parasite.

These trematodes belong to the Heterophyidae. Stellantchasmus falcatus and S. amplicaecalis are parasites which rarely cause infection in humans. S. falcatus is found in Hawaii, Japan, Korea, the Philippines and Thailand. S. amplicaecalis has once been described in Taiwan. The worm has snails of the genera Stenomelania and Thiara as its first intermediate host. Subsequently various species of fish may become infected. Cats, dogs, rats and fish-eating birds are the normal final host. The adult worm is found in the intestine. There is insufficient experience of the treatment of human infestations, but praziquantel seems a logical choice.

The trematode Stictodora fuscatum belongs to the Heterophyidae. It was first described in 1988 (Japan, Korea). It is a parasite which has fish-eating birds as its normal final host. People become infected by eating fish infected with metacercariae. There are insufficient data to give therapeutic guidelines.

The trematode Watsonius watsoni belongs to the Paramphistomatidae. Various primates are its normal final host. The parasite very rarely causes infection in humans. Some infections have been described in Nigeria and Namibia. The worms are found on the mucosa of the small intestine. People are probably infected via metacercariae on water plants. There are insufficient data to give therapeutic guidelines.

Thorny-headed worms or Acanthocephala are unusual parasites of humans. They have no intestine and absorb food through their skin. At the front the animals have a mobile proboscis with hooks in rows pointing backwards. With these they attach themselves to the intestinal epithelium of their normal final host. They can move about by waving the muscular proboscis back and forth. Thorny-headed worms have separate sexes. The eggs reach the outside world in the faeces of the final host. They then need to be eaten by the intermediate host (a crustacean or insect). For further development it is necessary for the intermediate host to be eaten by the final host (a vertebrate). Some species have more than one intermediate host. Most thorny-headed worms live less than one year.

Acanthocephalus rauschi is a thorny-headed worm which infects humans very rarely. The life cycle is unknown. It is assumed that infection may result from swallowing an intermediate host or a paratenic host. The parasite is found in the peritoneum.

Thorny-headed worms belonging to the genus Bolbosoma may infect humans very exceptionally. Two cases have been reported from Kyushu, Japan. The adult parasite is found in the jejunum and may cause acute peritonitis by perforating the intestinal wall. Possibly the presence of countless hooks on the proboscis and the anterior, thickened part of the body of this parasite play a part in this. The life cycle is not yet completely clear, but probably marine crustaceans are first intermediate hosts, fish are second intermediate hosts and whales are final hosts.

This is a thorny-headed worm which has been reported in humans. Corynosoma strumosum is probably a pseudoparasite.

Macracanthorhynchus ingens is a thorny-headed worm which normally parasitises carnivores such as raccoons and skunks. Various arthropods, frogs and snakes are intermediate hosts. M. hirudinaceus is a thorny-headed worm which was previously classified as a nematode. Nowadays it is classified in the Archiacanthocephala. The normal final host is the pig. Wild pigs can also become infected, as can dogs and monkeys. The parasite is cosmopolitan, with the exception of Western Europe. The adult worms are large: female worms are up to 35 cm long, males measure up to 10 cm. They are coloured pink and the cuticula is transversely folded so that it appears segmented. The proboscis has 6 rows of hooks. The female parasite lays some 80,000 eggs per day. The eggs measure 67-110 x 40-65 micrometers and have a thick, dark brown shell. When the eggs reach the outside world in the faeces, they are consumed by beetle larvae which feed on pig dung. The parasites then undergo a number of development stages: from acanthor to acanthella to cystacanth. These stages are completed in the beetle in 3 to 6 months. When a pig eats an infected beetle, the cystacanth excysts in the intestine and attaches itself to the intestinal wall. The prepatent period is 2 to 3 months. Infections in humans occur very rarely. If infected beetles are eaten by humans (e.g. as an ingredient in traditional medicine), the parasites attach to the intestinal mucosa. The parasites penetrate the intestinal wall and thus reach the peritoneum. Using its proboscis which is covered in hooks, the parasite attaches itself firmly, after which there is inflammation and granuloma formation. The result is acute abdominal pain, eosinophilic enteritis and possibly intestinal perforation with peritonitis and abscess formation. Diagnosis is made by laparotomy or by detecting eggs in the faeces. Praziquantel is active against the worm.

Moniliformis moniliformis is a thorny-headed worm which occasionally infects humans, in Japan and elsewhere. It belongs to the Acanthocephala. It has a cosmopolitan distribution. Various insects, including cockroaches, are intermediate hosts. Amphibians, reptiles and rodents (rats) may become parasitised by feeding on these parasitised arthropods. The adult parasite is found in the small intestine.

The thorny-headed worm Pseudoacanthocephalus bufonis is probably a pseudoparasite.

Armillifer armillatus, A. moniliformis and A. grandis belong to the Pentastomida or tongue-worms. The taxonomical classification of these organisms is not clear. These parasites are sometimes regarded as related to Crustacea (Branchiura), the evidence being the characteristic structure of the sperm cells. Pentastomids are hermaphroditic. Infection with A. armillatus frequently occurs in foci, certainly in Congo. Various mammals are intermediate hosts. Pythons and adders are the normal final hosts. The parasites are found in the respiratory passages of these reptiles. People become infected by eating an infected snake, by taking infected food or water. The nymphs are found in the liver, spleen, lungs and under the conjunctiva. Comma-shaped calcifications may be observed on an X-ray of the abdomen. The infection is also known as porocephalosis and is usually without symptoms if the parasites are only located in the abdomen. If located in the eye the parasite should be surgically removed.

Infections with Linguatula serrata are not common, but do occur in many areas. This parasite belongs to the Pentastomida. A number of herbivores are intermediate hosts. Carnivores are the normal final host. The larvae are found in tissue cysts, chiefly in the mesenteric lymph nodes and the adults in the respiratory system and sinuses. If the adults attach to the human throat, they produce acute respiratory problems and local swelling. Mechanical removal of the parasite solves the problem.

To date only one case of infection with Pentastoma najae has been reported. This parasite belongs to the Pentastomida. The normal hosts are snakes. People become infected by eating an infected snake or by eating food contaminated with snake secretions.

Worms of the genus Bipalium belong to the Turbellaria. Turbellaria are free-living, non-parasitising ciliate worms. Bipalium fuscatum, B. kewense and B. venosum are pseudoparasites which are of no importance in medicine.