Direct (non-vector) transmission of West Nile virus in geese.

During a recent epizootic, losses due to West Nile virus (WNV) infection in young goose flocks were estimated to be far greater than expected if mosquito-borne transmission was the principal route of infection. Contact transmission was investigated experimentally as an alternative explanation. A group of 10, 3-week-old geese were inoculated subcutaneously and placed in one insect-proof room with 20 geese of the same age. A group of 10 geese were housed in an adjacent insect-proof room to serve as an environmental control. All geese in the inoculated group produced antibodies, eight became viraemic and five died between 7 and 10 days after infection. Virus was shed from the cloaca and oral cavity by three geese. Two of the in-contact birds died on days 10 and 17 after infection, and WNV was recovered from another three birds. None of the environmental control group became infected. This result strongly suggests that horizontal transmission of WNV can occur in commercial flocks and may be aggravated if cannibalism and feather-picking of sick geese occur.