Avian influenza viruses in shorebird hosts at the Delaware Bay migratory stopover site
Maxted, Angela Marie
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Although waterfowl and gulls are recognized natural hosts to avian influenza viruses (AIV), AIV circulation in shorebirds is poorly understood. Shorebird infections primarily occur during spring in one species (Ruddy Turnstones; Arenaria interpres morinella) at one location worldwide (Delaware Bay, USA); close proximity to poultry production areas raises concerns about transmission to poultry. During May–June 2006–2008, we collected samples for virus isolation or serology from 3,233 individuals of 13 Charadriiformes species to better define patterns of AIV infection and exposure at Delaware Bay. Ruddy Turnstones were infected most often and with diverse subtypes. Prevalence and subtypes in Turnstones varied with year; prevalence was highest mid-season and among heavier-than-expected birds. Antibody prevalence increased over the season; together, these results suggested a local epidemic and recovery. Prevalence in Sanderlings (Calidris alba) was positively correlated with prevalence in Turnstones and subtypes matched between species, likely representing AIV spillover into Sanderlings. Red Knots (Calidris canutus rufa) had rare infections and high antibody prevalence that declined over the season; likely, they were exposed recently prior to arrival at Delaware Bay and partially immune to re-infection. Gulls also had rare infections but some subtypes were not found in other species, indicating partial gene pool separation between shorebirds and gulls. A radiotelemetry study of Ruddy Turnstones and Sanderlings revealed differences in habitat use that possibly account for variable infection and exposure; Turnstones routinely used salt marsh which might better support AIV transmission than beach habitat shared by all species. Radiotagged birds selected areas farther from agricultural land and poultry operations than expected, suggesting limited AIV transmission risk. Prevalence declined prior to departure, suggesting limited carriage of AIV onto breeding grounds. Analysis of individual Ruddy Turnstone resighting data revealed no difference in 1-year survival rates between AIV-infected and uninfected birds. Due to their susceptibility, temporary abundance in spring, and lack of morbidity or mortality, we propose that Ruddy Turnstones act as a local amplifying host for AIV acquired from resident waterfowl and gulls or from other migratory shorebirds. Additional studies are needed to further define shorebird species’ roles in global AIV epidemiology.