Research on vectors undertaken at ANSES

Some arthropods (a family that includes insects and arachnids) such as ticks and mosquitoes can transmit pathogens that cause diseases in animals, plants and/or humans. Several ANSES laboratories are studying vector-borne diseases transmitted to animals and the ability of vectors to transmit these pathogens. 

ANSES's work on vectors includes research and reference. Here is an overview of the work carried out by the laboratories: 

  • the Maisons-Alfort Laboratory for Animal Health works on pathogens transmitted by ticks, mosquitoes, sandflies and Culicoides, in order to identify and characterise them with the aim of combating their harmful effects. It examines the ability of ticks to transmit disease and the interactions between pathogens and vectors;
  • the Laboratory for Rabies and Wildlife studies the eco-epidemiology of tick-borne infectious agents. This work aims to improve understanding of their epidemiological cycles in wildlife and host-vector-pathogen interactions. Another objective is to understand the distribution of ticks and the infectious agents they carry, as well as the factors influencing these distributions. Lastly, the Laboratory examines situations where humans are at risk of exposure to tick bites and their infectious agents. In particular, the Laboratory's work includes the study of tick-borne encephalitis virus;
  • the Plant Health Laboratory studies insect vectors of plant pathogens and the diseases they transmit. Since 2019, it has been European Union Reference Laboratory for insects and mites. In this capacity, it leads a network of 28 laboratories located throughout the European Union and trains them in analytical methods for identifying and recognising 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, the subject of multiple studies

Ticks are the most common vectors of pathogens responsible for infectious diseases in 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 tick control methods. Here is an overview of the results of three examples of our research:

Tick-borne encephalitis, a widespread disease

Tick-borne encephalitis is one of the diseases that ticks can transmit to humans. More frequent in Eastern Europe, contaminations by the virus in France have mostly been observed in Alsace, where it is responsible for a few dozen cases of tick-borne encephalitis each year. In the wild, the virus circulates between ticks and rodents. To gain a better understanding of the epidemiology of this virus in Alsace, ANSES's Nancy Laboratory for Rabies and Wildlife and Laboratory for Animal Health have been monitoring its presence in ticks and rodents on the same site for several years. Their study shows 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 disappeared from the study area between 2016 and 2018, which could be explained by adverse weather conditions for the survival of tick larvae and nymphs or an increase in deer, which are among the main hosts of tick nymphs. 

While all human contaminations recorded in France to date have been due to the bites of ticks infected with the virus, a first case of contamination via consumption of infected food products occurred in 2020, in an area where circulation of the virus was previously unknown: 44 people living in the Ain département became infected after consuming raw goat's milk cheese. Goats infected with the virus can shed it for several days in their milk. Several ANSES laboratories took part in an investigation of the suspected farm, to study the exposure of goats to the virus. The results showed that the animals had access to undergrowth contiguous with a forest, where infected ticks were found. A quarter of the goats had antibodies to tick-borne encephalitis virus. This first case of foodborne infection in France underlines the lack of knowledge of the virus's distribution and the need for further studies on the risk associated with the consumption of raw milk products from animals infected with tick-borne encephalitis virus.  

Verifying whether European soft ticks can transmit African swine fever 

African swine fever (ASF) is a fatal disease of domestic pigs and wild boar. It arrived in Europe in 2007, and is not present in France at the current time. It is native to sub-Saharan Africa, where it is transmitted to warthogs by soft ticks of the genus Ornithodoros. These species are not found in France, but a related species lives in the south of the European continent. The Ploufragan-Plouzané-Niort Laboratory conducted research into whether this European tick could transmit the African swine fever virus. First finding: ticks do host 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 another route of transmission: the presence of ticks in the feed given to pigs. This trial was conclusive; pigs that had ingested ticks became ill. However, there is virtually no likelihood of this mode of contamination occurring in France, as the ticks of the species in question live only in the Iberian Peninsula. The results of this research were used in an ANSES report on the ability of different arthropod vectors to transmit the ASF virus. While other species, such as the Stomoxys biting fly, are better candidates than the tick for transmitting the virus, this mode of contamination presents a very low risk of transmission compared to the risk from direct contact between animals or with contaminated equipment.

Studying tick rehydration to develop new control methods

When not attached to a host, ticks are very susceptible to dehydration. To avoid this, they have a mechanism that allows them to absorb moisture from the air: in the event of drought, their salivary glands produce saliva that can absorb ambient moisture. This crystallises above the mouthparts. When environmental conditions improve, these saliva crystals absorb moisture from the air and liquefy, then are swallowed by the ticks, rehydrating them. Much of this water is directly absorbed by cells in the salivary glands. Until recently, it was not known how this process was controlled. Scientists at the Maisons-Alfort Laboratory for Animal Health have identified the neuronal mechanism controlling the uptake of water by the salivary glands. They have also shown 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 lead to the development of new products that specifically kill ticks by preventing them from rehydrating.