We evaluated the ability of three mosquito species (Aedes caspius, Aedes detritus, Culex pipiens), collected in southern France and Tunisia, and of different laboratory-established colonies (Aedes aegypti, Aedes albopictus, Aedes vexans, Anopheles gambiae, Culex pipiens, Culex quinquefasciatus) to disseminate two strains of Rift Valley fever virus (RVFV), the virulent ZH548 and the avirulent Clone 13. After feeding on an infectious blood meal at 10(8.5) plaque-forming units/mL, females were maintained at 30 degrees C for 14 days. Surviving females were tested for the presence of virus on head squashes. Disseminated infection rate corresponds to the number of females with disseminated infection among surviving females. Among field-collected mosquitoes, Cx. pipiens was the most susceptible species with disseminated infection rates ranging from 3.9% to 9.1% for French strains and up to 14.7% for Tunisian strains. Among laboratory-established colonies, Ae. aegypti from Tahiti exhibited the highest disseminated infection rates: 90% when infected with ZH548 and 72.6% with Clone 13. The presence of competent Cx. pipiens in southern France and Tunisia indicates the potential for RVFV epizootics to occur if the virus was introduced into countries of the Mediterranean basin.

West Nile fever (WNF) and Rift Valley fever (RVF) are emerging diseases causing epidemics outside their natural range of distribution. West Nile virus (WNV) circulates widely and harmlessly in the old world among birds as amplifying hosts, and horses and humans as accidental dead-end hosts. Rift Valley fever virus (RVFV) re-emerges periodically in Africa causing massive outbreaks. In the Maghreb, eco-climatic and entomologic conditions are favourable for WNV and RVFV emergence. Both viruses are transmitted by mosquitoes belonging to the Culex pipiens complex. We evaluated the ability of different populations of Cx. pipiens from North Africa to transmit WNV and the avirulent RVFV Clone 13 strain. Mosquitoes collected in Algeria, Morocco, and Tunisia during the summer 2010 were experimentally infected with WNV and RVFV Clone 13 strain at titers of 107.8 and 108.5 plaque forming units/mL, respectively. Disseminated infection and transmission rates were estimated 14–21 days following the exposure to the infectious blood-meal. We show that 14 days after exposure to WNV, all mosquito st developed a high disseminated infection and were able to excrete infectious saliva. However, only 69.2% of mosquito strains developed a disseminated infection with RVFV Clone 13 strain, and among them, 77.8% were able to deliver virus through saliva. Thus, Cx. pipiens from the Maghreb are efficient experimental vectors to transmit WNV and to a lesser extent, RVFV Clone 13 strain. The epidemiologic importance of our findings should be considered in the light of other parameters related to mosquito ecology and biology.

Physiological and molecular characteristics of natural populations of Culex pipiens Linnaeus, 1758 (Diptera: Culicidae) were investigated to elucidate how this species is potentially involved in the transmission of West Nile virus in Tunisia. A total of 215 Cx. pipiens females from 11 breeding habitats were analysed in the laboratory to estimate autogeny and stenogamy rates. They were tested individually for the locus CQ11 to distinguish between the two Cx. pipiens forms, pipiens and molestus. All tested Cx. pipiens populations were stenogamous. Females from underground breeding sites were all autogeneous, whereas females from above-ground habitats were mostly anautogeneous. Of all the females tested, 59.7% were identified as pipiens, 22.4% as molestus, and 17.9% as hybrid pipiens/molestus. Furthermore, both Cx. pipiens forms and their hybrids were found to co-occur in sympatry in all sites. The results of this study represent the first evidence that both Cx. pipiens forms and their hybrids are present in Tunisia. Because hybrids able to act as bridge vectors are present in all studied habitats, Tunisia can be considered to have a high degree of receptivity for the establishment of West Nile virus zoonotic cycles.