A stochastic model to study rift valley fever persistence with different seasonal patterns of vector abundance: New insights on the endemicity in the tropical island of Mayotte

Rift Valley fever (RVF) is a zoonotic vector-borne disease causing abortion storms in cattle and human epidemics in Africa. Our aim was to evaluate RVF persistence in a seasonal and isolated population and to apply it to Mayotte Island (Indian Ocean), where the virus was still silently circulating four years after its last known introduction in 2007. We proposed a stochastic model to estimate RVF persistence over several years and under four seasonal patterns of vector abundance. Firstly, the model predicted a wide range of virus spread pat- terns, from obligate persistence in a constant or tropical environment (without needing verti- cal transmission or reintroduction) to frequent extinctions in a drier climate. We then identified for each scenario of seasonality the parameters that most influenced prediction variations. Persistence was sensitive to vector lifespan and biting rate in a tropical climate, and to host viraemia duration and vector lifespan in a drier climate. The first epizootic peak was primarily sensitive to viraemia duration and thus likely to be controlled by vaccination, whereas subsequent peaks were sensitive to vector lifespan and biting rate in a tropical cli- mate, and to host birth rate and viraemia duration in arid climates. Finally, we parameterized the model according to Mayotte known environment. Mosquito captures estimated the abundance of eight potential RVF vectors. Review of RVF competence studies on these species allowed adjusting transmission probabilities per bite. Ruminant serological data since 2004 and three new cross-sectional seroprevalence studies are presented. Transmis- sion rates had to be divided by more than five to best fit observed data. Five years after introduction, RVF persisted in more than 10% of the simulations, even under this scenario of low transmission. Hence, active surveillance must be maintained to better understand the risk related to RVF persistence and to prevent new introductions. (Résumé d'auteur

Towards a better understanding of Rift Valley fever epidemiology in the south-west of the Indian Ocean.

International audience: Rift Valley fever virus (Phlebovirus, Bunyaviridae) is an arbovirus causing intermittent epizootics and sporadic epidemics primarily in East Africa. Infection causes severe and often fatal illness in young sheep, goats and cattle. Domestic animals and humans can be contaminated by close contact with infectious tissues or through mosquito infectious bites. Rift Valley fever virus was historically restricted to sub-Saharan countries. The probability of Rift Valley fever emerging in virgin areas is likely to be increasing. Its geographical range has extended over the past years. As a recent example, autochthonous cases of Rift Valley fever were recorded in 2007--2008 in Mayotte in the Indian Ocean. It has been proposed that a single infected animal that enters a naive country is sufficient to initiate a major outbreak before Rift Valley fever virus would ever be detected. Unless vaccines are available and widely used to limit its expansion, Rift Valley fever will continue to be a critical issue for human and animal health in the region of the Indian Ocean

Cytoplasmic Incompatibility as a Means of Controlling Culex pipiens quinquefasciatus Mosquito in the Islands of the South-Western Indian Ocean

The use of the bacterium Wolbachia is an attractive alternative method to control vector populations. In mosquitoes, as in members of the Culex pipiens complex, Wolbachia induces a form of embryonic lethality called cytoplasmic incompatibility, a sperm-egg incompatibility occurring when infected males mate either with uninfected females or with females infected with incompatible Wolbachia strain(s). Here we explore the feasibility of the Incompatible Insect Technique (IIT), a species-specific control approach in which field females are sterilized by inundative releases of incompatible males. We show that the Wolbachia wPip(Is) strain, naturally infecting Cx. p. pipiens mosquitoes from Turkey, is a good candidate to control Cx. p. quinquefasciatus populations on four islands of the south-western Indian Ocean (La Réunion, Mauritius, Grande Glorieuse and Mayotte). The wPip(Is) strain was introduced into the nuclear background of Cx. p. quinquefasciatus mosquitoes from La Réunion, leading to the LR[wPip(Is)] line. Total embryonic lethality was observed in crosses between LR[wPip(Is)] males and all tested field females from the four islands. Interestingly, most crosses involving LR[wPip(Is)] females and field males were also incompatible, which is expected to reduce the impact of any accidental release of LR[wPip(Is)] females. Cage experiments demonstrate that LR[wPip(Is)] males are equally competitive with La Réunion males resulting in demographic crash when LR[wPip(Is)] males were introduced into La Réunion laboratory cages. These results, together with the geographic isolation of the four south-western Indian Ocean islands and their limited land area, support the feasibility of an IIT program using LR[wPip(Is)] males and stimulate the implementation of field tests for a Cx. p. quinquefasciatus control strategy on these islands

Inventory of mosquitoes in Mayotte, French Departement in the Indian Ocean

Mayotte is an island situated in a region of the world particularly exposed to vector borne diseases. Several potential vectors, a tropical climate, an increasing urbanization, important movements of populations in the region, are among the relevant factors which favour the endemicity, the emergence or the re-emergence of vector transmitted diseases. Many vector born diseases are transmitted by mosquitoes: malaria, dengue, chikungunya, Rift Valley fever and, in the past, the Bancroftian filariosis. A collaborative project was recently initiated between IRD and ARS-OI to update the inventory of the mosquito species present in Mayotte. With the final goal to facilitate an integrated control against vector born diseases transmitted by mosquitoes, an entomological survey was performed in 2011 from March 21st till April 8th, at the end of the rainy season, with special attention in the best-protected natural areas. The breeding sites positive for preimaginal mosquitoes were geolocalised with a GPS and its environment was characterized. A semi-individual breeding of specimens was realized in the insectary from larval and pupal stages. Some mosquitoes were put in collections and the others were put in alcohol to allow further genetic researches by DNA sequencings, in Montpellier. The data concern 27 visited sites, and 426 points of collections. Our provisional results count 26 species (among 36 previously listed). A noticeable result is the discovery of Aedes (Stegomyia) nov. sp., belonging to a new species for Mayotte and for the science, collected in the humid forest at the top of the island (forest reserve of Majimbini) near the locality "The convalescence"

Inventory of mosquitoes in Mayotte, French Departement in the Indian Ocean

Mayotte is an island situated in a region of the world particularly exposed to vector borne diseases. Several potential vectors, a tropical climate, an increasing urbanization, important movements of populations in the region, are among the relevant factors which favour the endemicity, the emergence or the re-emergence of vector transmitted diseases. Many vector born diseases are transmitted by mosquitoes: malaria, dengue, chikungunya, Rift Valley fever and, in the past, the Bancroftian filariosis. A collaborative project was recently initiated between IRD and ARS-OI to update the inventory of the mosquito species present in Mayotte. With the final goal to facilitate an integrated control against vector born diseases transmitted by mosquitoes, an entomological survey was performed in 2011 from March 21st till April 8th, at the end of the rainy season, with special attention in the best-protected natural areas. The breeding sites positive for preimaginal mosquitoes were geolocalised with a GPS and its environment was characterized. A semi-individual breeding of specimens was realized in the insectary from larval and pupal stages. Some mosquitoes were put in collections and the others were put in alcohol to allow further genetic researches by DNA sequencings, in Montpellier. The data concern 27 visited sites, and 426 points of collections. Our provisional results count 26 species (among 36 previously listed). A noticeable result is the discovery of Aedes (Stegomyia) nov. sp., belonging to a new species for Mayotte and for the science, collected in the humid forest at the top of the island (forest reserve of Majimbini) near the locality "The convalescence"

A new species of Aedes (Stegomyia) from Mayotte, French over-sea Department in the Indian Ocean

International audienceA new mosquito species of Aedes of the subgenus Stegomyia has been recently discovered in Mayotte. This finding occurred during a comprehensive inventory of the mosquito species in this island of the Comoros archipelago. Scutum of Aedes nova specie Comparison with the three others species of Stegomyia in Mayotte Aedes simpsoni gr

A new species of Aedes (Stegomyia) from Mayotte, French over-sea Department in the Indian Ocean

International audienceA new mosquito species of Aedes of the subgenus Stegomyia has been recently discovered in Mayotte. This finding occurred during a comprehensive inventory of the mosquito species in this island of the Comoros archipelago. Scutum of Aedes nova specie Comparison with the three others species of Stegomyia in Mayotte Aedes simpsoni gr