The order of rodents ("Rodentia") is a large, successful group among mammals. To date, more than 1750 species have been described. Rodents represent approximately 25% of all mammalian families, approximately 35% of all mammalian genera and approximately 50% of all mammal species. The best known are the house mouse, the brown and the black rat, but squirrels, beavers, hamsters, gerbils, porcupines, lemmings and guinea pigs also belong to this group. Some animals are sometimes regarded as rodents by lay people, although they are in different taxonomic groups: rabbits (Lagomorpha), hedgehogs, moles and shrews (Insectivora). Most rodents are active at night. They have good hearing, and a good sense of touch and smell. Rodents are present on all continents and in very widely different biotopes: from arctic tundra to tropical deserts, woods, mountains, rivers, underground and around or in human dwellings. Most rodents are small and this helps them to exploit diverse microhabitats. There are climbers, diggers, runners, jumpers and swimmers. Many live in holes as protection against predators and for thermal insulation (water loss in dry climates!). Many rodents have very long Henle’s loops in their kidneys and can excrete therefore strongly concentrated urine. Several species do not drink but meet their water requirements from food and via metabolic water (carbohydrates are broken down into CO₂ and H₂O). Some species hibernate. Several rodents reproduce quickly with early sexual maturity, short gestation times (in mice 20 days, rats 22 days). There are many young per litter and the animals have repeated pregnancies. Although not all rodents reproduce quickly, this is the case in those species, which cause problems (and are therefore called plague species). Some rodents form complex social structures, such as prairie dogs, marmots and naked mole rats.

Most medically significant rodents belong to the Muridae and the Cricetidae. Rodents play a part in many diseases, such as plague, transmitted by the rat flea Xenopsylla cheopis and Weil's disease, a severe form of leptospirosis transmitted via infected rat urine. Rodents play a part in conditions such as echinococcosis (E. multilocularis), trichinellosis, Lyme borreliosis, recurrent fever (Borrelia recurrentis), salmonellosis, rat bite fever, tularemia, lymphocytic choriomeningitis, Hymenolepis diminuta and rickettsioses such as RMSF, scrub typhus and murine typhus. Haemorrhagic fevers that are transmitted by rodents ("rodent-borne") include Hantaviruses and Arenaviruses such as Junin, Machupo and Lassa fever. Infection with Penicillium marneffei is essentially a disease of rodents, but can occur in AIDS patients in Southeast Asia. In 2003 an imported and infected Gambian giant rat spread monkeypoxvirus in the USA, a country where there had been no cases untill that moment.

Just as significant is the economic damage caused by rodents, such as damage from gnawing food crops, stored products, buildings, cables and household goods. Often the cost of clearing the damage is many times greater than the price of the food eaten or the spoiled faeces-contaminated products. Muskrats cause a great deal of damage to dykes and canal banks. Some rodents are useful. A number of animals are raised for their valuable pelts, such as chinchillas and muskrats while others are kept as pets. Guinea pigs are often eaten in South America. A research programme is currently underway to find out whether Cricetomys gambianus can be used to detect land mines.

Numerous laboratories use mice and rats as experimental animals, to gain knowledge which would otherwise be impossible or very difficult to obtain. Today, working with experimental animals is avoided as much as possible, but alternative in vitro experiments are not always available. Rodent strains have been bred to provide experimental models for, e.g. immune deficiency, increased likelihood of forming tumours or hypertension, etc. These strains are maintained by inbreeding. These strains are usually identified by the original developer using a combination of letters and/or figures. This code may refer to the initials of the centre or the researcher. A forward slash in the code refers to a substrain, a further development of the original strain, which is indicated to the left of the slash. The code may also refer to a specific characteristic, such as, for example, BL for black, nu for nude (hairless, immune deficient, mice lacking a thymus).

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The structure of the muscles of the chewing apparatus, and particularly the insertion of the masseter muscle, is used to divide the various rodents into suborders. In squirrels, the lateral masseter moves the jaw forwards and the deep masseter closes the mouth. In guinea pigs, the lateral masseter closes the jaw and the deep masseter moves the jaw forwards. In mice, both components of the masseter are used to move the jaw forwards and both contribute to gnawing. In rodents, the lower jaw can be placed in two positions. Either the animals gnaw with their incisors, or they chew with their molars. They cannot do both simultaneously.

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The chewing apparatus in mammals is complex. Depression of the lower jaw requires little force, because gravity does most of the work. The digastric muscle originates in the region of the ear and its insertion is into the internal ventral side of the mandible. It can open the mouth with force. The temporal muscle originates on the lateral side of the skull and inserts on the coronoid process of the mandible. The masseter has a deep and a superficial part. This muscle connects the cheekbone with the most posterior lateral part of the lower jaw. The pterygoid muscles originate on the underside of the skull behind the palate. The muscle fibres run obliquely and laterally to the medial side of the angle of the lower jaw. Contraction of one muscle moves the angle of the lower jaw to the middle and the lower jaw sidewards (to the other side). Bilateral contraction moves the lower jaw forwards. This permits chewing (molars grinding against each other). Mammals are unique in that they can chew food on one side (left or right). In many mammals, the left and right lower jaws are connected at the chin by a bony bridge (mandibular symphysis) so that they can use the muscles of both jaws to exercise force on one side. In herbivores, the temporal muscle and coronoid process are not very well developed but the ramus of the lower jaw is very well developed. The temperomandibular joint is high above the line of the teeth, unlike in carnivores. This is useful in crushing food. The mandibular condyles have various forms and orientations, which permit anterior-posterior and medial-lateral movements.

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The digestive system of the rodent is also adapted to its way of life. Rodents are mostly herbivores, although there are exceptions. Rattus norvegicus is omnivorous, others are insectivorous (Lophuromys), carnivorous and/or ichtyovorous (meat-eating resp. fish-eating, e.g. Ichtyomys, Hydromys, Anotomys). Vegetable food is frequently overly plentiful and does not run away. On the other hand the energy that is present in vegetable material is lower than that in meat or fish. The protein content is frequently low and the proteins are surrounded by a tough cellulose wall. Specialised teeth can grind plants down finely but no mammal has its own cellulase and no mammal can therefore break down cellulose itself. The efficient use of the food requires, therefore, that the cellulose be broken down by symbiotic micro-organisms in the animal’s intestine. This problem is solved in two ways by plant-eating mammals, as described below.

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Ruminants such as cows and antilopes eat large quantities of grass that is stored in a large stomach, the rumen. This is where the large mass is moistened, kneaded and mixed with symbiotic micro-organisms. Fermentation starts here. The larger plant parts proceed from the rumen to the reticulum and are regurgitated in order to be chewed again. Once it has been chewed again the food pulp returns to the rumen. The finely minced grass can now pass into the reticulum and then to the omasum, from which it moves to the acid abomasum. This is where the next step of digestion by the usual enzymes takes place. The symbiotic micro-organisms are also digested giving an extra source of energy. This digestive mechanism is very efficient but the quantity of food that can be processed is limited. If the food is too poor and if therefore large quantities of it have to be processed, these animals find it very difficult. Vegetable toxins can be broken down in the rumen but large quantities of tannins or resins in the food can have a negative effect on the symbionts.

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Rodents and other "posterior intestine-digesters" such as horses and elephants solve the problem in another way. The stomach is simple, but they have an enormous caecum, a blind-ending type of diverticulum at the junction of the small intestine and the colon. Digestion takes place in this caecum. Then the pulp enters the colon where further absorption of useful components takes place. The transit time in the intestine is short, so that undigested components are quickly excreted. This digestive mechanism is less efficient than that of the ruminants but the animals can quickly process large quantities of very low quality food, which is important if the food contains large quantities of unusable material such as silica, resins or tannins. The faeces still contain small quantities of useful material. Some animals therefore also occasionally use faeces as food. Coprophagia frequently occurs among rodents. This naturally promotes transmission of pathogenic organisms among a population of rodents.

A total of more than 1750 species of rodents are known. Most of these species have a rat or mouse-like appearance. It is not easy to distinguish between all these species. Sometimes there are clear external characteristics such as size, colour, tail length, shape of the head, etc. but in many cases they resemble each other very closely. Often they can be distinguished on the basis of detailed cranial characteristics (morphometry) but sometimes this too is not sufficient and the shape and number of chromosomes or even protein electrophoresis or DNA-sequencing have to be used. Correctly naming a particular species can appear to be irrelevant when confronted with a rodent problem, but identification can be extremely important. In the African genera Tatera and Mastomys, for example, there are species that can occur together and cannot be distinguished one from the other by external features. However, they play completely different roles in transmitting bubonic plague.

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If rodents are collected for identification, it is important to have the taxonomic identification confirmed by specialists in museums and/or universities. For this, preserved specimens are necessary. Apparently similar anatomical structures can have developed independently of each other in the course of evolution (convergent evolution), which makes taxonomy much more difficult. The details as regards classification can therefore differ considerably from author to author, which illustrates the uncertainties in this area. The following brief summary should not be regarded as being exhaustive or final. The last three are often regarded as one suborder (Hystricomorpha). Many animals are still "insertae sedis"; their taxonomic position is unclear, e.g. the springhare (sometimes classified among the Petidae).

Several alternative classifications are possible.

If a rodent has already been identified as a reservoir of a particular pathogenic organism, it should be described in detail.

• Geographical distribution of the animals. This determines the maximum area in which the disease can occur. If the disease occurs outside this area, additional reservoirs will have to be sought. The importance of taxonomy is absolutely clear here. See the problems of Lassa fever and the chromosomal subtypes in Mastomys natalensis.
• Geographical distribution of the pathogen in the rodent population. This determines the area in which the disease can be endemic. This area is not always the same as the one above. In addition to this, the geographical range can be dynamic, not static. We want to know how many animals carry a certain pathogen, as well as which and how many ectoparasites they have (see X. cheopis-index in plague).
• Regional distribution of the animals (various biotopes and habitats). It was found, for example, that Calomys musculinus (the corn mouse and reservoir for Junin virus) is rarely actually found in corn fields but in the more stable marginal habitats at the sides of roads and fields. Mowing or burning this vegetation can be expected to reduce the risk of Argentinian haemorrhagic fever.
• Determination of the relative prevalence of infection (e.g. males vs females, young vs old animals). Horizontal instead of vertical transmission has been found for Hantaviruses. The pathogenic organism can be transmitted from animal to animal via wounds, such as occur in fights among males. Transplacental antibodies can protect young animals.
• Longitudinal prospective studies were carried out in order to find out the variations in time, both seasonal fluctuations and year-to-year variations. Population explosions can greatly affect the incidence of disease. Catching, tagging and releasing studies are used to gain an understanding about growth, migrations, reproductive conditions and infection status over time. Environmental variables such as temperature, rainfall and vegetation are recorded. The type of traps and bait used for catching the animals vary from species to species. Sometimes "remote tracking" is used, in which small radio transmitters are attached to animals in order to better record their migrations. Supplementary studies attempt to clarify their diet, reproduction and genetic variations and the age structure of the rodent population. For the latter, among other things, wear and tear on the jaws and the weight of the eye lens are measured (lenses grow throughout life in rodents).
• With all these data it should be possible to set up a mathematical model, in order to predict flare-ups and issue warnings.

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Example: In the summer of 1993 in a rural area of the southwest of the USA there were suddenly numerous cases of an acute pulmonary syndrome with a high mortality rate. The cases occurred in groups (in time and geographically). The virus responsible was identified fairly rapidly (Sin Nombre virus). Because it appeared to be genetically related to Hantaan virus that is spread by rodents, a rodent reservoir was suspected. This was found in Peromyscus maniculatus (the deer mouse). Retrospectively it was discovered that a population explosion of these small rodents brought them into increased contact with man. The increase in the number of rodents was caused by an exceptional harvest of Piñon seeds (Pinyon pines, Pinus sp.), an important source of food for the animals. This rich harvest was in turn stimulated by favourable climate circumstances.

Here we will discuss briefly a number of genera, some species of which play an important role in the epidemiology of animal diseases. However it is only a very restricted list with very limited information.

The European wood mouse belongs to this genus, but medically is not of particular significance. Other types of Apodemus, such as the large wood mouse in the southeast of Europe and the black-striped field mouse in the Far East, are carriers of dangerous types of Hantavirus.

These voles (such as A. terrestris) are an important host for Echinococcus multilocularis. This parasite is also known as fox tapeworm and can cause a very serious infection in man. Foxes eat infected rodents and people are infected by coming into contact with fox droppings.

This genus includes some types of voles in the moderately temperate regions of the northern hemisphere. They occur mainly in natural or wild biotopes. The bank vole (campagnol roussâtre) is the most important reservoir species for Hantavirus in northern and western Europe.

This is the most common type of rodent in sub-Saharan Africa. There are various species which are very hard to distinguish. The species that are important for agriculture and public health are M. natalensis (in southern Africa, East Africa and probably in West Africa as well), M. erythroleucus and M. huberti (both from West and East Africa) and M. coucha (southern Africa). In the medical literature they are often all, incorrectly, called M. natalensis. Sometimes the whole genus is considered to be a group within the genus Praomys and a species name such as Praomys natalensis is regularly found in the literature. These are large mice (about 40 g on average) that occur in large numbers in varied biotopes, with high densities in fields and villages. The English name is multimammate rat because of the fact that most species have a large number of teats (up to 24), corresponding to the maximum number of young in a litter. This high reproductive capacity explains to a great extent their status as pests. Population explosions occur irregularly, usually after years with exceptional rainfall. Certain species of Mastomys are the reservoir for Lassa virus and also play an important role in the transmission of plague.

This genus includes most voles ("campagnols"). They are usually herbivorous, quite small rodents that occur in all the temperate zones of the northern hemisphere. Some cause problems in agriculture and forestry but they can also be carriers of infectious diseases such as Echinococcus multilocularis (fox tapeworm).

The two species of the modern house mice (Mus musculus and Mus domesticus) both originate in the border areas between Iran and Russia. The animals have spread with man for the last ten thousand years, together with the ascent of farming. They are small rodents (less than 30 g) that occur all over the world, nearly always near people. They can cause considerable damage to food stocks that have been stored and also to infrastructure. In Australia and China they sometimes reach plague densities in large agricultural areas. Certain mites are parasites of mice and can transmit rickettsial pox. Lymphocytic choriomeningitis is another disease that can be transmitted from house mice to man.

Muskrats (Ondatra zibethicus; Cricetidae) are large rodents. They spend a large part of their lives in fresh water. Their laterolateral flattened tail helps them to swim. They can transmit Omsk haemorrhagic fever. Muskrats came originally from North America. They were introduced into Europe in the 19th century for their valuable pelts. The animals were released into the wild but were able to adapt very well to the local conditions. They reproduced very rapidly. Because of their habit of digging holes in dykes and the banks of canals, these semi-aquatic animals now pose a very serious economic threat. In some areas muskrats are eaten. They may play a role in the spreading of Echinococcus multilocularis (fox tapeworm).

This genus includes a number of different species of mice in North America. Some species occur only in natural habitats, but some occur in large numbers in agricultural areas or also in and near dwellings. They cause quite a lot of damage and nuisance. They are reservoirs for diseases such as Lyme borreliosis (transmitted by ticks) and some Hantaviruses (for example Sin Nombre virus).

The black rat (Rattus rattus) originates from Southeast Asia. The brown rat (Rattus norvegicus) has its origins in Central Asia, and not in Norway as its scientific name might suggest. In Southeast Asia other species occur that can cause serious problems in agriculture. R. norvegicus and R. rattus have spread all over the world. They are found almost everywhere where there are people. They are quite large rodents (black rat ± 150 g; brown rat >200 g). The black rat has characteristic large transparent ears and a tail that is usually as long as or even longer than its body. The brown rat has small non-transparent ears and a shorter tail. They cause serious damage to food supplies or infrastructure such as drains and sewers. They play a part in the transmission of all sorts of infectious diseases such as leptospirosis and plague. The black rat is an excellent climber and is often found in high places (grain lofts, silos, etc), while the brown rat prefers to live on the ground and also often in damp places (such as sewerage systems). Both species of rat are very common and are often transported along with cargo in ships. Cargo ships (such as grain ships) are therefore regularly fumigated with cyanide. Several different strains of lab rats have been bred which have proven to be of immens value for medical research.

Tatera sp. are quite large African rodents that are found in natural habitats and in fields. Locally, they can cause considerable damage to agriculture. Some species are reservoirs of plague.

Rodent control is not always necessary everywhere. Sometimes they do occur in and near dwellings and places where food is stored, as well as in places where there is a lot of refuse and rubbish. In order to control a problem caused by rodents, it is first necessary to identify the species correctly. Signs of gnawing, holes, faeces, tracks left by their feet and tails, etc, give an initial idea of which species is involved. For example, rats that eat cereals gnaw a grain at the pointed end, while mice will start to gnaw a grain in the middle. The scale of the problem must also be established.

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1. General environmental hygiene is the first measure to be taken to prevent contact and infestation. Potential sources of food must be made inaccessible. Comfortable nesting areas and areas in which rodents can run must be avoided as much as possible. Potential nesting material, abundant ground vegetation near dwellings, rubbish, piles of material next to walls inside or outside must be cleared away. In order to prevent further infestation in dwellings, after removing the rubbish and waste material, it is advisable for so-called rat-proofing measures to be introduced.

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2. In and around dwellings and storage areas it is important that access for rats and mice is restricted. This means that the buildings have to be sealed as much as possible (no gaps under doors, no holes in the walls, broken pipes, etc.). Food and food waste must be stored in such a way as to be inaccessible to rats and mice. Examples are closed boxes, jars with lids, rodent-proof packaging. In third-world countries, food storage areas are built on high poles which are surrounded with horizontal thin steel plates or wires with sharp pins or razor blade wire.

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3. If rodents are still present, they must be controlled by physical means (traps, catching them) or chemical means. Cats can often keep the densities of peridomestic rodents low but they are not suitable for dealing with a population explosion and can sometimes even play a role in transferring diseases from rodents to man. Devices with high-pitched sounds (whether these are ultrasound or not) have no effect. Other methods such as introducing rodent diseases, rodent birth control, etc. are not to be recommended or have not yet been adequately investigated.

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4. When rodents are controlled by poisoning or by traps in which the animals are killed, the carcasses must be removed and buried or burnt. Direct contact with the dead animals is best avoided, particularly if the presence of rodent diseases is suspected. If diseases occur which are carried by rodents through ectoparasites (e.g. plague), it is very important that, before controlling the rats, the vector should be controlled by means of insecticides. Otherwise the ectoparasites will leave the dead rats and look for a new host. This promotes disease transmission.

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5. Rodenticides are chemicals which, usually formulated into an edible bait, are consumed by the animals, as a result of which, sooner or later, they die. Sometimes the poison is applied as a contact powder so that it gets onto the animals’ coats and they lick it off during grooming. These agents are almost always also toxic to other mammals (including man) and often also to birds, so that great care is required in their use. Rodents which live underground can be killed by blowing toxic fumes into their burrows systems, but this has to be done by specialised staff. This type of fumigation is sometimes also used to derat aeroplanes, ships and containers.

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6. Expertise and care are needed to prepare bait. A correct dose of the active principles in the bait is not only important because of safety aspects, but particularly because, if the dose is too high, rodents do not want to eat the bait and if the dose is too low, they will not die. The bait itself is important because it determines how attractive the poison is to the rodents. Different vehicles are required depending on the type of rodent and the circumstances (loose grains, pastes, paraffin blocks, etc.). When putting down the poison, care has to be taken that it cannot be reached by other animals or children. This is best achieved by offering the bait in "bait containers" such as boxes, tubes, bamboo stems, pieces of corrugated iron, etc. which are accessible to rats but not to other animals.

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7. In the first half of the twentieth century, rapid-acting "single dose" poisons were mainly used for controlling rats and mice. This method gives fairly poor results. The reason for this is that many rats have a so-called "new object reaction". If the animals come across something new in their environment, e.g. bait, they will very carefully try a small amount of it to test it and will then ignore it. In the following days they will eat more and more of it if they feel well. After four to five days they will then accept the bait fully. If the animals do not feel well, the surviving animals as well as their nest companions will no longer touch the bait (probably there is communication via smell). Attemps were made to circumvent this by "pre-baiting", initially setting out non-poisonous bait, but the results were not very good.

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8. After 1950 anticoagulants were developed as rat poison. Dicoumarol was discovered in the 1920s as causing a haemorrhagic disease in cattle which had eaten spoilt white sweet clover (Melilotus alba). This plant belongs to the Papilionaceae family. It contains melilotoside, a glucose-coumarin compound. This pleasant-smelling glycoside (Lat. "mellitus" = honey, sweet) occurs in sweet-smelling plants such as scented woodruff (Galium odoratum), sweet vernal grass (Anthoxanthum odoratum) and holy grass (Hierochlöe odorata) also known as vanilla grass in North America. If certain fungi such as Penicillium sp. and Aspergillus sp. act on the moistened macerated plant (e.g. fungal growth when wet hay is stored), the glycoside can be converted into the more active dicoumarol. This substance is a natural anticoagulant. A variant of dicoumarol was developed by the Wisconsin Alumni Research Foundation and, on account of this, was given the name warfarin. This is an antagonist of vitamin K. Vitamin K is essential for producing a number of coagulation factors (the letter "K" comes from the German "Koagulation"). Vitamin K is necessary for placing an extra acid group (COO^--group) on the side-chain of glutaminic acid (so-called gamma-carboxylation of glutaminic acid) in the precursor protein chain of prothrombin and factors VII, IX and X. This side-group is an important Ca⁺⁺ binding site. If insufficient vitamin K is active, these coagulation factors are not able to bind Ca⁺⁺ and it will not be possible to activate them. Protein C and S are vitamin K-dependent inhibitors of the coaguation cascade

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Warfarin and related products such as coumachlor, coumatetryl, diphacinone and chlorophacinone can be used as rodenticides because they cause fatal bleeding in the animals. The symptoms only appear after several days. Rats and mice prefer to eat grain. Therefore poisoned grain is often used as bait. With the newer, stronger products such as difenacoum, bromadialone and certainly brodifacoum, flocoumafen and difethialone, a single dose is normally sufficient. The effects are, however, not apparent until a few days have passed. The animals mostly die in hidden places after one to five days. The products are on the market under different trade names and are mostly bought as ready-prepared bait. Predators which eat poisoned animals are also at risk of being poisoned. These poisons are also dangerous to man, but vitamin K1 (phytomenadione) is a suitable long-acting antidote. If serious problems threaten, coagulation factors or whole blood should be given via infusion.

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Anticoagulantia-resistance in rodents is a controversial subject. The term is often used to describe diminished sensitivity in a rodent population, as opposed to individual animals. In a number of places, resistance has developed to a number of anticoagulants. Due to chance mutations, individuals may occur in a rat population that are less sensitive to poisoning by anticoagulants. Because most of the other rats die from the poison, these resistant rats can reproduce in greater numbers, on account of which the hereditary resistance characteristics spread rapidly through the population. To date, resistance is known to occur to almost all anticoagulants, except for the most toxic, brodifacoum, flocoumafen and difethialone. Rats that are resistant to one anticoagulant are usually also resistant to the other weaker anticoagulants. Resistance is a well-known problem in large parts of Great Britain, Germany and Denmark. In other places resistance is less well documented, but that also depends to a great extent on the degree to which the problem has been examined and which anticoagulants are used.

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9. Another frequently used rodenticide is sodium monofluoroacetate ("compound 1080") but because of its high toxicity, its use in most countries is strictly regulated. There is no antidote to this fast-acting poison.

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10. Zinc phosphide (Zn₃P₂) is also sometimes used as a rodenticide. It is a black powder smelling of onions and garlic which is usually bought as a concentrate and is then mixed with milled grain, for example. In damp conditions it evaporates quickly and gives off the poisonous gas phosphine (PH₃). It is cheap and the rats die within half an hour, which can be an important psychological stimulus for the user in that he finds the dead rats quickly. For the same reason, however, the use of acute poisons is to be discouraged in circumstances where ectoparasites transmit diseases.

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11. Alpha chloralose is a poison which is used to control mice. It reduces the metabolism thereby causing fatal temperature loss (lethal hypothermia). This effect is however only efficient at low environmental temperatures (<16°C). Alpha chloralose is therefore often used in cold storage areas, etc. It is not suitable for rat control. It is less poisonous for larger mammals because these animals can more easily maintain their body temperature. On the other hand, the agent is very poisonous to small birds.

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12. Other : High doses of calciferol (vitamin D) causes a disturbance in the calcium balance in the body resulting in death after a few days. It is a very efficient rodenticide, but also very poisonous for other mammals including man. Other less frequently used poisons are norbormide, Red Squill and scilliroside, bromethalin and strychnine. The use of a number of old products such as arsenic oxide is strongly discouraged. In some countries Salmonella is used on a large scale as a way of controlling rodents. There is a specific strain of Salmonella which is supposed to only contaminate rodents and which, mixed with grain, is offered as bait. This method is fairly efficient and cheap but in view of the risk of contaminating man or other animals, its use is advised against by the World Health Organisation.

• Keep food, including pet food and water, covered and store in sturdy containers which rodents cannot gnaw through.
• Waste and rubbish bags should be stored in similarly sturdy containers. These are best kept in a raised place. Extra rat-proofing can be introduced.
• Do not leave uneaten food lying around, including pet food.
• Rubbish (hiding places) should be cleared up, not only in cellars and kitchens but also around the house, chicken runs, play areas, etc.

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• Place strong wire screens in front of small openings or close them. Cracks and gaps should be sealed. A thick layer of gravel under a pile dwelling considerably reduces tunnelling.
• Strong metal plates can be buried around the dwelling (e.g. sheets of corrugated metal normally used for roofs). They should be at least 30 cm under the ground.
• Use a cement base for wood piles, sheds and huts, etc.
• Use traps and/or rodenticides. When using rodenticides, great care must be exercised to ensure that non-target poisonings do not occur. Rodenticides are therefore not recommended around food or animal feed (such as hay).
• Grass should be mown short, there should be no thick bushes around the dwelling.
• Never place a tent or sleeping bag near possible hiding places (nests, holes, wood piles, rubbish dumps, etc.). Preferably do not sleep on the ground but on a raised camp bed.

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• Places with dead rodents or their excreta must be thoroughly cleaned. This also applies when hikers or campers use a hut that has been empty for a long time. Hantavirus can survive for a fairly long time in dust that contains dried infected urine. Use water with bleach, Lysol or other decontaminants when cleaning. Do not dry brush or use a vacuum cleaner since this causes an aerosol effect and people can become infected if they breathe in this dust. Wear face masks, protective clothing and gloves. Wash hands afterwards with soap. Adventurous travellers should never pitch their tents or sleeping bags near possible hiding places (nests, holes) or near wood piles, rubbish dumps or other places which can attract animals.
• Do not pick up dead rodents with bare hands. Put the bodies in a strong plastic bag. Bury them or remove them with the other rubbish.
• Military personel moving into previously unoccupied buildings during campaings, have to take sensible precautions.