Experimental transmission of West Nile Virus and Rift Valley Fever Virus by Culex pipiens from Lebanon.

Renée Zakhia,Marie Vazeille,Nabil Haddad,Anna-Bella Failloux,Laurence Mousson,Remi Charrel

doi:10.1371/journal.pntd.0005983

Renée Zakhia, Marie Vazeille + Show 4 more

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https://doi.org/10.1371/journal.pntd.0005983

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Abstract

West Nile virus (WNV) and Rift Valley fever virus (RVFV) are two emerging arboviruses transmitted by Culex pipiens species that includes two biotypes: pipiens and molestus. In Lebanon, human cases caused by WNV and RVFV have never been reported. However, the introduction of these viruses in the country is likely to occur through the migratory birds and animal trades. In this study, we evaluated the ability of Cx. pipiens, a predominant mosquito species in urban and rural regions in Lebanon, to transmit WNV and RVFV. Culex egg rafts were collected in the West Bekaa district, east of Lebanon and adult females of Cx. pipiens were experimentally infected with WNV and RVFV Clone 13 strain at titers of 1.6×108 and 1.33×107 plaque forming units (PFU)/mL, respectively. We estimated viral infection, dissemination and transmission at 3, 7, 14 and 19 days post infection (dpi). Results showed that infection was higher for WNV than for RVFV from 3 dpi to 19 dpi. Viral dissemination and transmission started from 3 dpi for WNV; and only from 19 dpi for RVFV. Moreover, Cx. pipiens were able to excrete in saliva a higher number of viral particles of WNV (1028 ± 405 PFU/saliva at 19 dpi) than RVFV (42 PFU/saliva at 19 dpi). Cx. pipiens from Lebanon are efficient experimental vectors of WNV and to a lower extent, RVFV. These findings should stimulate local authorities to establish an active entomological surveillance in addition to animal surveys for both viruses in the country.

Highlights

West Nile virus (WNV) and Rift Valley fever virus (RVFV) are two important emerging mosquito-borne zoonotic agents transmitted by Culex pipiens, a complex of sibling species that includes Cx. pipiens s.s., Cx. quinquefasciatus and possibly Cx. australicus [1, 2]
West Nile virus (WNV) and Rift Valley fever virus (RVFV) are two emerging mosquitoborne arboviruses mainly transmitted by Culex mosquitoes
RVFV is mainly distributed in Sub-Saharan Africa but epizootics were reported in Egypt, Saudi Arabia and Yemen

Summary

Introduction

West Nile virus (WNV) and Rift Valley fever virus (RVFV) are two important emerging mosquito-borne zoonotic agents transmitted by Culex pipiens, a complex of sibling species that includes Cx. pipiens s.s., Cx. quinquefasciatus and possibly Cx. australicus [1, 2]. Cx. pipiens s.s. includes two biotypes or subspecies: Cx. pipiens pipiens and Cx. pipiens molestus [1, 3]. The first biotype is primarily a bird-feeding mosquito present in temperate areas while Cx. pipiens biotype molestus feeds on mammals (mainly human) and thrives in sewers in temperate and sub-tropical regions [3, 4]. WNV infections have been reported in many tropical and temperate countries in Africa, Europe, Asia and America. The Middle East and North Africa (MENA) region has been long considered as a WNV-endemic area [8, 9]. Acquired cases have been recently reported in Israel [10], Greece [11], Turkey [12], and Italy [13]. The introduction of WNV into the United States in 1999, which constitutes a turning point in WNV epidemiology, is thought to have originated from Israel following introduction from Africa [16, 17]

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