The isolation of influenza A viruses and paramyxoviruses from feral ducks in New Zealand.

Tracheal and cloacal swabs from apparently healthy ducks, gulls, shearwaters and terns in New Zealand were tested for myxoviruses by inoculation into embryonated eggs. Seven influenza A viruses belonging to three antigenic subtypes (H4N6; H1N3; H11N3) and nine paramyxoviruses of two antigenic subtypes (PMV-1; PMV-4) were isolated from feral ducks. The occurrence of the same virus subtypes in birds, including ducks, in other countries suggests that they were introduced into New Zealand by the importation of infected poultry or game birds. Ducks experimentally infected with two of the influenza A virus isolates excreted virus in their faeces for 12 days. Infection with H4N6 subtype prevented reinfection with the same subtype but not with a different one (H11N3).