It's the first case in Yakima County and in Washington State. Yakima Health District officials say a Yakima resident has been diagnosed with West Nile virus. FIRST A HORSE NOW A HUMANOfficials say the human case comes after a report of West Nile virus disease in a horse from Yakima County announced by Washington State Department of Agriculture last week. Health officials say the person was likely exposed to infected mosquitoes in Yakima County. There is a vaccine for horses to prevent against West Nile virus infection; speak with your veterinarian for more information.