Section: New Results

Wolbachia and Dengue

Wolbachia is a genus of bacteria which infects arthropod species, including a high proportion of insects. It is one of the world's most common parasitic microbes and is possibly the most common reproductive parasite in the biosphere. Wolbachia is a maternally inherited endosymbiont of a large number of insects and other arthropods that induces various effects on host reproductive biology. Estimated to infect more than 60% of all insect species Wolbachia species are present in mature eggs, but not mature sperm. Only infected females pass the infection on to their offspring. Another consequence of infection is cytoplasmic incompatibility, i.e., the inability of Wolbachia-infected males to successfully reproduce with uninfected females.

The successful introduction of a life-shortening strain of Wolbachia into the dengue vector Aedes aegypti that halves adult lifespan has recently been reported.

Mosquitoes carrying this Wolbachia strain show around a 50% reduction in adult female lifespan compared to uninfected mosquitoes. It has been reported that wMel and wMelPop-CLA strains block transmission of dengue serotype 2 (DENV-2) in Aedes aegypti, forming the basis of a practical approach to dengue suppression. Infection by Wolbachia has a triple effect : reduction of recruitment, increasing of mortality for the mosquitoes and reduction of dengue transmission.

With our colleague of Brazil (see International cooperation) we built and study different models for the introduction of Wolbachia in a population of Aedes aegypti. These models are epidemiological models with vertical transmission only, which is quite new. We found that bistabilty does exist : three equilibria are present. We show that the coexistence equilibrium is unstable. We show that the equilibrium without infection and the equilibrium with the whole population infected are asymptotically stable. Numerical experimentation shows that the basin of the second equilibrium is appreciable. This indicates that introduction of Wolbachia is feasible. The connection of theses models with transmission models of dengue is under investigation by the French-Brazilian team.