Pathological, entomological, avian and meteorological investigation of a West Nile virus epidemic in a horse farm.

Pathological, entomological and avian investigations were conducted during the summer of 2002, in a horse farm that had four cases of West Nile virus (WNV) infection in horses. All the four horses had encephalitis and WNV infection was confirmed by RT-PCR and in situ hybridization procedure. Forty-seven per cent of house sparrows that resided on the farm were tested positive for WNV infection. Mosquitoes (98%Culex pipiens) collected by trapping at the farm, during this period were positive for WNV. The meteorological data for year 2002 were compared to previous 16 years. The precipitation and atmospheric temperature were found to be reduced and higher respectively, indicating a drier summer than the prior 16 years, which may have been a contributing factor for the outbreak. None of the horses on these premises had been vaccinated for WNV disease.