Research
Insecticide resistance and malaria transmission :
Mosquito control through the use of insecticides is still the most important component of malaria control programs. Insecticide resistance jeopardizes disease control efforts by increasing the number of mosquitoes that survive the insecticide treatment and are available to spread the parasite in the population. Although this quantitative effect of insecticide resistance on the mosquitoes may be mitigated by the costs associated to insecticide resistance, it has been deemed sufficiently worrying to motivate the development of resistance management strategies to prevent or retard the spread of resistance. Little attention has however been given to the potential qualitative effects of insecticide resistance on the mosquitoes: are insecticide resistant mosquitoes better, equal or worse vectors of diseases than susceptible ones? Mosquitoes are not mere flying syringes, they provide a very specific physiological environment in which the parasites differentiate, proliferate and migrate to the correct tissues to ensure transmission to the next host. There is increasing evidence that this environment is drastically modified when insects become resistant to insecticides. Insecticide resistance can have an effect on parasites by interfering with mosquito immunity, by increasing or decreasing the oxidative damage to the parasite or by depleting the resource pool needed for parasite development, amongst others.
The Culex-bird malaria system is a great experimental model to test whether the evolution of insecticide resistance can have an impact on the transmission of the disease. First, because C. pipiens is one of the species in which insecticide resistance has been best characterized at the genetic and molecular levels. Some of the mechanisms of insecticide resistance found in C. pipiens are in fact identical to those found in Anopheles gambiae and An. albimanus, the main vectors of diseases of malaria in Africa and South America, respectively. Second, because avian malaria and human malaria are very similar, phyllogenetically and life history-wise. And third, because both the parasite and the mosquito are present at our doorstep; in the Montpellier region, there are well-identified populations of insecticide resistant and susceptible C. pipiens mosquitoes and there is a high prevalence (30-80%) of bird malaria in (at least) blue tits. Our project (which is financed through an ANR grant of the French government) combines physiological, behavioural, molecular and life history approaches, lab work and field work, all within an evolutionary ecology framework.
Selected papers:
Rivero A, Vézilier J, Weill M, Read AF, Gandon S (2010) Insecticide control of vector borne diseases: when is insecticide resistance a problem? PLoS Pathogens 6(8): e1001000.
Plasmodium-Wolbachia interactions in the mosquito :
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Competition between parasites within a host is a major evolutionary force in infections. The presence of two parasites inside a host often results in an antagonistic interaction between them. Antagonistic interactions can be due to a competition for space and/or resources between the different parasites, to the production of substances that are directly toxic to the competitor or to the presence of non-specific immune effectors. This type of interactions between parasites within vectors can have drastic consequences for disease transmission.
C. pipiens mosquitoes are infected by Wolbachia, a vertically transmitted symbiotic bacterium that induces cytoplasmic incompatibility. Recent work has shown that a Wolbachia infection render Drosophila flies more resistant to a range of viral infections. In addition, Aedes aegypti mosquitoes have been recently transinfected with a strain of Wolbachia of Drosophila origin, and similar efforts are being carried with Anopheles mosquitoes. In Aedes, a Wolbachia strain of Drosophila origin has been shown to shorten the life of mosquitoes and to interfere with the development of dengue and chikungunya viruses, opening up interesting possibilities for the use of Wolbachia as a disease control method. As Wolbachia are vertically transmitted, however, it is expected that their virulence will decrease over time. Culex and Wolbachia have had a long evolutionary history. The aim of our project is to determine whether a long-standing infection by Wolbachia interacts with the malaria parasite (P. relictum) in Culex mosquitoes.
