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Abstract
West Nile virus (WNV) threatens the health of humans and equines worldwide. Culex (Cx.) pipiens complex mosquitoes are major vectors but numerous other species have been implicated. Due to variations in blood-feeding behaviour, Cx. pipiens biotypes and hybrids influence transmission, from enzootic cycles (between mosquitoes and birds), to spill-over transmission to humans and equines. In this study, mosquitoes were collected in May–June 2018 during the early period of the transmission season from two regional units of Greece, where WNV cases had been reported in the previous four years (Palaio Faliro and Argolida). A total of 1062 mosquitoes were collected with Biogents Sentinel 2 traps collecting both a greater number of all mosquito species and the Cx. pipiens complex than CDC miniature light traps or Heavy Duty EVS traps. Molecular identification confirmed additional species including Aedes albopictus. The proportion of Cx. pipiens biotypes in Palaio Faliro was 54.5% pipiens, 20.0% molestus and 25.5% hybrids. In Argolida, the collection comprised 68.1% pipiens biotype, 8.3% molestus biotype and 23.6% hybrids. Screening resulted in WNV detection in three females of the pipiens biotype and in one hybrid. As hybrids play a role in spill-over transmission, these findings highlight the importance of entomological surveillance programs incorporating molecular xenomonitoring as an early warning before human cases at the onset of the transmission season.
Highlights
West Nile virus (WNV) is an arbovirus belonging to the Japanese encephalitis serocomplex within the Flavivirus genus (Flaviviridae family) and is the most widespread flavivirus, with circulation worldwide, including the USA and Europe [1,2,3,4]
Sampling during the onset of the 2018 WNV at pre-disease stage in the Regional Units (RUs) in the Attica and Peloponnese regions was important in a year in which more than 300 human cases were recorded in Greece
Previous studies have demonstrated the importance of hybrids as bridge vectors of WNV
Summary
West Nile virus (WNV) is an arbovirus belonging to the Japanese encephalitis serocomplex within the Flavivirus genus (Flaviviridae family) and is the most widespread flavivirus, with circulation worldwide, including the USA and Europe [1,2,3,4]. Natural transmission of WNV mainly occurs in enzootic cycles between birds and competent ornithophilic mosquito vectors, with avian species being the principal maintenance and amplifying hosts of WNV as many species develop sufficient viremia for onward transmission [5,6,7]. Spill-over transmission can occur when competent vectors feed on humans or horses. During natural transmission both humans and horses are considered dead-end hosts since they cannot sustain sufficient viraemia. Infection in humans does pose a transmission risk due to the possibility of iatrogenic transmission through blood and tissue donations, in addition to the possibility of intrauterine transmission or WNV being passed on through breast milk [4]. Currently no human vaccination is available, vaccination of horses has been shown to reduce clinical disease within this species [12,13]
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