One of ANSES’s missions on vectors is research and reference. Overview of the work carried out by the laboratories:
- the Maisons-Alfort animal health laboratory works on pathogens transmitted by ticks, mosquitoes, sandflies and culicoides, in order to identify and characterize them, with the aim of combating their harmful effects. He works on the ability of ticks to transmit diseases and the interactions between pathogens, vectors and their microbiome.
- the rabies and wildlife laboratory studies the eco-epidemiology of infectious agents transmitted by ticks. It thus aims to better understand their epidemiological cycles within wildlife and the host-vector-pathogen interactions. Another objective is to know the distribution of ticks and the infectious agents they harbor, as well as the factors influencing these distributions. Finally, the laboratory is interested in situations at risk for humans of exposure to tick bites and their infectious agents. As part of its work, the laboratory studies in particular the tick-borne encephalitis virus;
- the plant health laboratory studies insect vectors of plant pathogens and the diseases they transmit. Since 2019, it has been a reference laboratory for the European Union for insects and mites. In this capacity, he runs a network of 28 laboratories located throughout the European Union and trains them in analytical methods to identify and recognize insects, including insect vectors.
Other laboratories study vector-borne diseases on a more ad hoc basis, such as the Ploufragan-Plouzané-Niort laboratory, which took part in research on the role of ticks in the transmission of African swine fever.
Focus on ticks, an object of multiple research
Ticks are the most important vectors of pathogens responsible for infectious diseases for humans and animals in Europe. Several ANSES laboratories are studying the bio-ecology of these vectors and the pathogens they transmit. Work is also being carried out on means of combating ticks. Presentation of the results of three examples of searches:
Tick-borne encephalitis, a disease that is spreading
Tick-borne encephalitis is one of the diseases that ticks can transmit to humans. More common in Eastern Europe, contamination by the virus in France is best known in Alsace, where the virus is responsible for a few dozen cases of tick-borne encephalitis each year. In nature, the virus circulates between ticks and rodents. In order to better understand the epidemiology of this virus in Alsace, the rabies and wildlife laboratories of Nancy and Animal Health have monitored the presence of this virus in ticks and rodents on the same site over several years. It appears from their study that the virus circulates very little: only 0.03% to 0.3% of ticks are carriers and 2 to 5% of rodents have antibodies showing that they have been in contact with the virus. The virus has disappeared from the study area between 2016 and 2018, which could be explained by unfavorable weather conditions for the survival of tick larvae and nymphs or an increase in deer, which are among the main hosts of tick nymphs.
If until now all the human contaminations recorded in France were due to bites of ticks infected with the virus, a first case of contamination via the consumption of contaminated food products took place in 2020 in an area where the circulation of the virus n was not known: 44 people living in Ain who had consumed raw goat’s milk cheese were infected. Goats infected with the virus can indeed excrete it for several days in the milk. An investigation into the suspected farm, in which various ANSES laboratories participated, was carried out in order to study the exposure of goats to the virus. The results show that the animals had access to an undergrowth in continuity with a forest, where infected ticks were found. A quarter of the goats had antibodies to tick-borne encephalitis virus. This first case of food-borne infection in France highlights the lack of knowledge on the distribution of the virus and the need to conduct further studies on the risk associated with the consumption of raw milk products from animals infected with the virus. tick-borne encephalitis.
Checking if European soft ticks can transmit African swine fever
African swine fever (ASF) is a fatal disease for domestic pigs and wild boars. Arrived in Europe in 2007, it is not present in France for the moment. It is native to sub-Saharan Africa, where it is transmitted to warthogs by soft ticks of the genus Ornithodoros. The species in question is not present in France, but a related species lives in the south of the European continent. The Ploufragan-Plouzané-Niort laboratory conducted research to find out if this European tick could transmit the African swine fever virus. First observation : ticks harbor the virus but do not transmit it to pigs when they bite them. However, the virus can remain infectious in the tick for several months. The scientists therefore tested a another way of contamination : the presence of ticks in the food given to pigs. The test was conclusive, the pigs having ingested ticks fell ill. However, the probability that this mode of contamination occurs in France is almost nil: ticks of the species considered live only in the Iberian Peninsula. The results of this research were used in an ANSES opinion (PDF) on the ability of different arthropod vectors to transmit the African swine fever virus. If other species, such as the stomox biting fly, are better candidates than the tick for transmitting the virus, the risk of transmission linked to this mode of contamination remains very low compared to that by direct contact between animals or with material. contaminated.
Study the rehydration of ticks to develop new means of control
When not attached to a host, ticks are very susceptible to dehydration. To avoid this, they have a mechanism allowing them to absorb humidity from the air: in the event of drought, their salivary glands produce saliva which has the property of absorbing ambient humidity. This crystallizes above the mouthparts. When environmental conditions become milder again, these crystals absorb moisture from the air and liquefy, then are swallowed by ticks, which rehydrates them. Much of this water is directly absorbed by cells of the salivary glands. Until recently, it was not known how this process was controlled. Scientists from the Maisons-Alfort Animal Health Laboratory have identified the neural mechanism that controls the reabsorption of water by the salivary glands. They also showed that a substance, vesamicol, is capable of disrupting this mechanism, by reducing the volume of water that ticks are able to absorb. This discovery could make it possible to develop new products that specifically kill ticks by preventing them from rehydrating.