All eyes on the tiger mosquito on World Mosquito Day

On 20 August, it is World Mosquito Day. We have long been working with various types of mosquitoes, the viruses they can transmit and methods to protect the population. One such mosquito is the Asian tiger mosquito. The invasive species has been claiming victims in Central and South America, Africa and Asia for years, but due to globalisation and climate change, it is now advancing into our region. Vigilance and action can slow its advance.

This year, ITM's National Reference Centre for Arboviruses recorded a record number of dengue cases. The 245 confirmed cases involved travellers returning from the tropics. In Belgium, unlike some southern European countries, there is no local transmission of the dengue virus yet. Nevertheless, vigilance is needed: returning travellers bring the virus with them, and the tiger mosquito is present.

Mosquito monitoring in Belgium

Since the start of the citizen science project MEMO+, more than 800 reports of suspected mosquito sightings have already been made. In six locations spread across Flanders, Brussels and Wallonia, these reports were confirmed to be the tiger mosquito. Isra Deblauwe, entomologist at the ITM, confirms: “The number of sightings has increased in recent years, and this trend is likely to continue. It is essential to map where the tiger mosquito occurs to assess the risk of virus transmission.” Last year, overwintering tiger mosquitoes were detected for the first time in two locations; now there are five. The spread of the tiger mosquito is inextricably linked to globalisation and climate change.

Climate change and dengue outbreaks

The impact of climate change is most evident in the Hindu Kush-Himalaya region of Nepal, one of the most diverse and fastest-warming regions in the world. Here there are regular outbreaks of mosquito-borne diseases, such as dengue. The knowledge gained by scientists here can be applied to other regions also affected by climate warming. ”The CLIMB project aims to take a multidisciplinary approach to investigate the interaction between different factors,” explains Dr Marco Brustolin, researcher in vector biology at ITM. ”In our highly secured insectary, we are investigating the viral diversity of tiger mosquitoes in Nepal, from lowland to highland regions and their ability to transmit the dengue virus in relation to their adaptability to climate change. This research will provide valuable insights into the impact of climate change on dengue virus and vector biodiversity.”

13,000 km away in south-central Cuba, the DI-MOB project focuses on understanding the transmission process of dengue. Here, the emphasis is not on the mosquito, but on behaviour. The number of dengue cases was historically low during the COVID-19 lockdown period. This unexpected result prompted a reassessment of the then-current mathematical models regarding the impact of human mobility on dengue outbreaks. To do so, the researchers analysed mobility data, socio-spatial characteristics of commuting and meeting places. “We always assumed that most dengue infections occurred indoors,” says Veerle Vanlerberghe, epidemiologist at ITM. “But the drop in infections during the pandemic showed that this assumption was wrong. We are now using data from mobile phone masts to investigate where people are most vulnerable to dengue. Our hypothesis is that schools and workplaces are high-risk areas because the tiger mosquito stings during the day.”

No ‘magic bullet’ against dengue

The tiger mosquito and dengue virus occur in different contexts, and there is no ‘magic bullet’ that can eradicate the virus. However, what does help is the commitment and involvement of communities. This can be achieved by removing breeding sites, educating children and young people through initiatives such as science podcasts or the EDUbox in collaboration with the Flemish Broadcasting corporation, and by raising awareness among travellers and doctors. If someone experiences fever after travelling to a (sub)tropical area, it is crucial to consult a doctor immediately. Physicians should inform their patients of the risks prior to travelling and advise them on precautionary measures. The free travel medicine app and website Wanda can help with this. “We detected more dengue cases than ever this year, but all patients had recently returned from a trip to a (sub)tropical country,” says Marjan Van Esbroeck, head of the reference laboratory at ITM. “By encouraging these patients to protect themselves from mosquito bites during their illness, for example with mosquito repellents, we can hopefully delay the local spread of the virus in Belgium for years to come.”

Dengue diagnostics

Although only a quarter of infected people develop symptoms, the challenge remains how to identify dengue quickly and accurately, and how to distinguish between its different types. Identifying the specific type of dengue can be life-saving. After an initial infection with one type of dengue, a person is at significantly higher risk of developing severe symptoms when infected a second time with a different type. This understanding is essential for effective patient follow-up and triage. Moreover, it plays a key role in vaccination programmes and outbreak monitoring.

There are two methods to detect dengue. The direct method detects the virus during the first week of infection, while the indirect method detects antibodies after that initial week. However, implementation of these diagnostic methods in low- and middle-income countries faces obstacles. High costs and complex technology pose major challenges, as does the fact that the virus can often only be detected in the first week of infection - a period when patients sometimes do not yet show symptoms. Distinguishing the different dengue types further complicates the process.

ITM is currently working on technologies to address these challenges. An affordable, specific and user-friendly rapid test to diagnose dengue as early as the first week is being developed in collaboration with the A-Sense Lab at the University of Antwerp.

Interest in multiplex testing is growing. These tests allow for the simultaneous detection of multiple viruses, such as dengue, chikungunya, Zika, yellow fever or Rift Valley fever. This is particularly valuable, as these diseases often present with similar symptoms, making quick and accurate diagnosis difficult. With multiplex testing, appropriate interventions - such as patient management, vector control and vaccination - can be initiated more swiftly.

At ITM, both direct and indirect multiplex detection methods are being developed. For example, Anne Hauner of the Virology Unit is researching multiplex PCR tests, while Joachim Mariën's Unit of Virus Ecology is working on a multiplex assay for 15 arboviruses on animal samples. These animals could potentially be a reservoir for these viruses, providing crucial insight into the spread of the disease.

The tiger mosquito and the viruses it can transmit pose a growing threat, partly due to global warming. To combat diseases such as dengue, an interdisciplinary approach, such as that of ITM, is crucial. Citizen involvement is also essential. By staying vigilant and actively working to eliminate breeding sites, we can collectively slow down the spread of these diseases. Developments in dengue detection and treatment represent a major step forward in the fight against this devastating disease. With the deployment of new technologies and innovative collaborations like those at ITM, there is increasing hope that one day we can effectively contain dengue, even in the most vulnerable regions of the world.