(Oklahoma City-AP) -- A state veterinarian says Oklahomans do not adequately vaccinate their horses against the West Nile virus.
State Veterinarian Burke Healey says fewer than one in four horses in the state are vaccinated against the virus.
Last year, West Nile killed 135 Oklahoma horses.
Cases of the virus in the horse population are expected to increase dramatically in September and October.
Veterinarians say a booster shot should be given this month to horses previously vaccinated.
There is no West Nile vaccine for humans.