State agriculture officials are urging horse owners to keep their horses' vaccinations updated.
Last year, there was only one confirmed case of West Nile Virus in horses and there were no cases of Eastern Equine Encephalitis. But the Virginia Department of Agriculture and Consumer Services says the number of horses affected in previous years and in other states was much higher.
The vaccinations last six to 12 months.
Officials also recommend destroying standing water breeding sites for mosquitoes, using insect repellents and removing animals from mosquito-infested areas from dusk to dawn, which is peak biting time.
West Nile Virus kills up to 30 percent of horses who contract it, while Eastern Equine Encephalitis kills up to 90 percent.
Owners also are urged to check about rabies vaccinations for their horses.