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

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Abstract
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 geesewere inoculated subcutaneously and placed in one insect-proof room with 20 geese of the same age. A group of10 geese were housed in an adjacent insect-proof room to serve as an environmental control. All geese in theinoculated group produced antibodies, eight became viraemic and five died between 7 and 10 days afterinfection. Virus was shed from the cloaca and oral cavity by three geese. Two of the in-contact birds died ondays 10 and 17 after infection, and WNV was recovered from another three birds. None of the environmentalcontrol group became infected. This result strongly suggests that horizontal transmission of WNV can occur incommercial flocks and may be aggravated if cannibalism and feather-picking of sick geese occur.