West\xa0Nile virus host-vector-pathogen interactions in a colonial raptor

Zoltán Soltész,Péter Fehérvári,László Papp,Katalin Szentpáli-Gavallér,Andrea Harnos,Tamás Bakonyi,Károly Erdélyi,Éva Horváth,László Kotymán,Ádám Dán,Péter Palatitz,Szabolcs Solt,Mónika Barna

doi:10.1186/s13071-017-2394-z

Abstract

BackgroundAvian host species have different roles in the amplification and maintenance of West Nile virus (WNV), therefore identifying key taxa is vital in understanding WNV epidemics. Here, we present a comprehensive case study conducted on red-footed falcons, where host-vector, vector-virus and host-virus interactions were simultaneously studied to evaluate host species contribution to WNV circulation qualitatively.ResultsMosquitoes were trapped inside red-footed falcon nest-boxes by a method originally developed for the capture of blackflies and midges. We showed that this approach is also efficient for trapping mosquitoes and that the number of trapped vectors is a function of host attraction. Brood size and nestling age had a positive effect on the number of attracted Culex pipiens individuals while the blood-feeding success rate of both dominant Culex species (Culex pipiens and Culex modestus) markedly decreased after the nestlings reached 14 days of age. Using RT-PCR, we showed that WNV was present in these mosquitoes with 4.2% (CI: 0.9–7.5%) prevalence. We did not detect WNV in any of the nestling blood samples. However, a relatively high seroprevalence (25.4% CI: 18.8–33.2%) was detected with an enzyme-linked immunoabsorbent assay (ELISA). Using the ELISA OD ratios as a proxy to antibody titers, we showed that older seropositive nestlings have lower antibody levels than their younger conspecifics and that hatching order negatively influences antibody levels in broods with seropositive nestlings.ConclusionsRed-footed falcons in the studied system are exposed to a local sylvatic WNV circulation, and the risk of infection is higher for younger nestlings. However, the lack of individuals with viremia and the high WNV seroprevalence, indicate that either host has a very short viremic period or that a large percentage of nestlings in the population receive maternal antibodies. This latter assumption is supported by the age and hatching order dependence of antibody levels found for seropositive nestlings. Considering the temporal pattern in mosquito feeding success, maternal immunity may be effective in protecting progeny against WNV infection despite the short antibody half-life measured in various other species. We conclude that red-footed falcons seem to have low WNV host competence and are unlikely to be effective virus reservoirs in the studied region.

Highlights

Avian host species have different roles in the amplification and maintenance of West Nile virus (WNV), identifying key taxa is vital in understanding WNV epidemics
All trapped individuals were females. As the latter two species had orders of magnitude lower abundance compared to Cx. pipiens and Cx. modestus we excluded them from further analyses
We did not trap any mosquitoes in control nest-boxes; other arthropods like canopy dwelling or non-parasitic nest substrate feeding species were trapped in small numbers

Summary

Introduction

Avian host species have different roles in the amplification and maintenance of West Nile virus (WNV) , identifying key taxa is vital in understanding WNV epidemics. West Nile virus (WNV) is the most widespread member of the arthropod-borne group of the genus Flavivirus, family Flaviviridae [1]. The virus is maintained in an enzootic cycle between vectors and avian hosts, while humans [14], equines [15] and other vertebrate taxa are predominantly dead-end hosts [16]. To assess human infection risks and predict the spatio-temporal patterns of disease outbreaks it is vital to better understand the complex avian hostmosquito vector transmission ecology of WNV [17, 18]. A wide array of bird species have been identified as potential virus amplifying hosts [19].

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