West Nile virus in Tunisia, 2014: First isolation from mosquitoes

Irrigation in arid areas of North Africa may lead to the emergence of West Nile virus which is likely to cause future sporadic and foreseeable outbreaks not only in Tunisia but along the migratory flyways of birds between Africa and Eurasia. Thus, setting up an entomological surveillance as an early alert system around the Mediterranean Basin to prevent future outbreaks is highly needed. New vector control methods should be evaluated in light of our findings. [Display omitted] •West Nile virus lineage 1 is circulating in mosquitoes in Tunisia.•Culex pipiens is the main vector of West Nile virus in the Western Mediterranean Basin.•The continued increase in irrigated areas in North Africa regions is of high importance as it is associated with the spread of mosquito vectors of West Nile virus. Several outbreaks of human West Nile virus (WNV) infections were reported in Tunisia during the last two decades. Serological studies on humans as well as on equine showed intensive circulation of WNV in Tunisia. However, no virus screening of mosquitoes for WNV has been performed in Tunisia. In the present study, we collected mosquito samples from Central Tunisia to be examined for the presence of flaviviruses. A total of 102 Culex pipiens mosquitoes were collected in September 2014 from Central Tunisia. Mosquitoes were pooled according to the collection site, date and sex with a maximum of 5 specimens per pool and tested for the presence of flaviviruses by conventional reverse transcription heminested PCR and by a specific West Nile virus real time reverse transcription PCR. Of a total of 21 pools tested, 7 were positive for WNV and no other flavivirus could be evidenced in mosquito pools. In addition, WNV was isolated on Vero cells. Phylogenetic analysis showed that recent Tunisian WNV strains belong to lineage 1 WNV and are closely related to the Tunisian strain 1997 (PAH 001). This is the first detection and isolation of WNV from mosquitoes in Tunisia. Some areas of Tunisia are at high risk for human WNV infections. WNV is likely to cause future sporadic and foreseeable outbreaks. Therefore, it is of major epidemiological importance to set up an entomological surveillance as an early alert system. Timely detection of WNV should prompt vector control to prevent future outbreaks. In addition, education of people to protect themselves from mosquito bites is of major epidemiological importance as preventive measure against WNV infection.