West Nile virus host-vector-pathogen interactions in a colonial raptor

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.

The Role of Birds of Prey in West Nile Virus Epidemiology

“…However, subsequent studies in the House sparrow suggest that maternally-derived antibodies decline rapidly, being undetectable after 9 days, and do not confer protection to the juvenile after this point [ 43 ]. Maternal antibodies were suggested as a potential reason for the absence of disease in Red-footed falcon ( Falco vespertinus ) nestlings in the presence of infected mosquito vectors [ 44 ]. Avian immunity research has focused on humoral immunity, i.e., the induction of antibodies.…”

Rift Valley Fever and West Nile virus vectors in Morocco: Current situation and future anticipated scenarios

“…The virus is maintained in nature by a mosquito–bird–mosquito transmission cycle, whereas humans and equines have become accidentally infected, but considered dead‐end hosts as they do not contribute largely to the infection spread. Birds and mosquitoes ( Culex and Aedes ) are both the important amplifying hosts and vectors that contribute largely to the re‐emergence and global spread of WNV (Komar et al., 2003; Levine et al., 2017; Soltész et al., 2017).…”

West Nile virus infection in horses in Saudi Arabia (in 2013–2015)

“…Although many mosquito species can transmit the virus, Culex species remains the major vector (Noden, Coburn, Wright, & Bradley, ; Shahhosseini et al, ; Soltesz et al, ). These Culex species of mosquitoes are also present in the Arabian Peninsula and they may play a role in sustaining the virus replication cycle (Cope et al, ; Sallam, Al Ahmed, Abdel‐Dayem, & Abdullah, ).…”