The epizootiology of anatid herpesvirus 1 infection in free-flying waterfowl: a comparison of latent and active infections among native waterfowl, captive-reared released ducks, and peridomestic or feral ducks.

The epizootiology of anatid herpesvirus 1 (AHV-1) infection in waterfowl is poorly understood but apparently involves persistence of the virus in latently infected birds. Epornitics have often occurred in captive waterfowl or semiwild ducks in parklike settings, and many wildlife professionals conclude that such ducks may be the source of infection for wild waterfowl. We assessed the prevalence of latent infection and viral shedding from four groups of waterfowl: naturally occurring populations of native waterfowl, captive-reared waterfowl released for shooting, introduced nonmigratory waterfowl (e.g., resident, wild Mallards; Anas platyrhynchos), and semiwild peridomestic waterfowl (e.g., park ducks) in North Carolina and Florida, USA from 2004 to 2009. A nested PCR assay was used to detect viral DNA in trigeminal ganglia and cloacal swabs. Detection of viral DNA in trigeminal ganglia, but not cloacal swabs, was assumed to indicate latent infection, whereas PCR-positive cloacal swabs indicated active shedding of the virus. We collected 2,045 samples from 23 species of native, wild waterfowl, and detected latent infections in nine species. Wild Northern Pintails (Anas acuta), a species reportedly resistant to the virus, had the highest prevalence (8.1%). However, low prevalences were identified in other waterfowl from various families. Cloacal shedding was rarely detected (0.1% prevalence) among native waterfowl and was observed in one Blue-winged Teal (Anas discors) and one Mottled Duck (Anas fulvigula). All captive-reared, released waterfowl (n=13) collected were Mallards and one was latently infected, suggesting that these birds could also serve as a source of AHV-1 for naive waterfowl. All nonmigratory waterfowl sampled (n=90) were also Mallards. None of the resident Mallards were shedding virus, but one was latently infected. The peridomestic waterfowl sampled included breeds of domestic Mallard (n=6) and Muscovy Ducks (Cairina moschata; n=73). One peridomestic Mallard and four Muscovy Ducks were shedding virus at the time they were sampled, but no latently infected, asymptomatic carriers were identified.