Serological, Molecular and Entomological Surveillance Demonstrates Widespread Circulation of West Nile Virus in Turkey

Abstract

West Nile virus (WNV), a mosquito-borne flavivirus with significant impact on human and animal health, has recently demonstrated an expanded zone of activity globally. The aim of this study is to investigate the frequency and distribution of WNV infections in potential vectors and several mammal and avian species in Turkey, where previous data indicate viral circulation. The study was conducted in 15 provinces across Turkey during 2011–2013. In addition, the entomological study was extended to 4 districts of the Turkish Republic of Northern Cyprus. WNV exposure was determined in humans, horses, sheep and ducks from Mersin, Sanliurfa, Van and Kars provinces of Turkey, via the detection of neutralizing antibodies. WNV RNA was sought in human and equine samples from Mersin, Adana and Mugla provinces. Field-collected mosquitoes from 92 sites at 46 locations were characterized morphologically and evaluated for viral RNA. Neutralizing antibodies were identified in 10.5% of the 1180 samples studied and detected in all species evaluated. Viral nucleic acids were observed in 5.9% of 522 samples but only in horses. A total of 2642 mosquito specimens belonging to 15 species were captured, where Ochlerotatus caspius (52.4%), Culex pipiens sensu lato (24.2%) comprise the most frequent species. WNV RNA was detected in 4 mosquito pools (1.9%), that comprise Oc. caspius Cx. pipiens s.l. and DNA barcoding revealed the presence of Cx. quinquefasciatus and Cx. perexiguus mosquitoes in infected Culex pools. All WNV partial sequences were characterized as lineage 1 clade 1a. These findings indicate a widespread WNV activity in Turkey, in Eastern Thrace and Mediterranean-Aegean regions as well as Southeastern and Northeastern Anatolia., West Nile virus (WNV), frequently transmitted to humans and other susceptible species via bites of infected mosquitoes, is a significant global public health threat. Limited information is available on WNV epidemiology in Turkey, located in the endemic zone of the agent around the Mediterranean Sea. This study was performed to reveal WNV activity in potential hosts and vector mosquitoes, involving 11 provinces in Turkey and the Turkish Republic of Northern Cyprus during 2011–2013. Our findings indicate virus exposure in humans and various animals in previously unexplored regions as well as a high rate of virus circulation in equine blood samples during the mosquito season. Field-captured mosquito specimens demonstrated the presence of major WNV vectors among 15 species identified. WNV infection was detected in 1.9% of the pooled mosquito specimens. Molecular characterization of the individual mosquitoes of the infected pools revealed Culex quinquefasciatus and Cx. perexiguus species, important WNV vectors where Culex quinquefasciatus not previously known to exist in Turkey. Partial viral genome sequences obtained from infected hosts were characterized as lineage 1, the predominant pathogenic WNV strain circulating in Europe as well as the American Continent.