2West Nile virus (WNV) mainly infects birds, horses and humans. Outcomes of the infection range from light uncharacteristic signs to fatal neurologic disease. The main objectives of the present study were to measure serum IgG and IgM antibodies in naturally exposed and vaccinated horses and to compare results of hemagglutination-inhibition test (HIT), enzymelinked immunosorbent assay (ELISA) and plaque reduction neutralization test (PRNT).Altogether 224 animals were tested with HIT for WNV antibodies and 41 horses were simultaneously examined with ELISA and PRNT. After primary screening for WNV antibodies, horses were vaccinated. Samples were taken immediately before and 3-5 weeks after each vaccination. McNemar chi-squared and percent agreement tests were used to detect concordance between HIT, ELISA and PRNT.Analyses by HIT confirmed the presence of WNV antibodies in 27/105 (25.71 %) from naturally exposed horses. Sera from 57/66 (86.36%) vaccinated animals were positive before the first booster and from 11/11 (100%) before the second booster. HIT was less sensitive when detecting IgG antibodies. We could detect post vaccination IgM in 13 cases with MAC-ELISA and in 7 cases with HIT.WNV is endemic in Hungary causing regular natural infections. Protective antibodies could not be measured in each individual case 12 months after primary injections; protection is more reliable after the first yearly booster. Based on our findings it was not be possible to differentiate infected horses from recently vaccinated horses using IgM antibody capture ELISA (MAC-ELISA). HIT does not substitute ELISA or PRNT when detecting IgG, but was useful tool in this study to gain statistical information about the tendencies within a fixed population of horses.
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.
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