Oklahoma horse owners are being encouraged to vaccinate their animals against the potentially deadly West Nile Virus and Eastern Equine Encephalitis diseases.
The Oklahoma Department of Agriculture, Food and Forestry reports about 40 cases in each of the past two years in which horses in the state have been infected with the diseases.
The diseases are often carried by birds and transferred to mosquitoes, which spread the viruses through bites to both horses and humans.
While there are vaccines for horses there are, as yet, no vaccines for humans.
The Oklahoma Department of Health says three more people have died from the West Nile virus.
The first mosquitoes of 2013 confirmed to be carrying the West Nile virus have been found in Oklahoma.
The Tulsa County Health Department said Thursday that a sampling of mosquitoes in Tulsa County have tested positive for the potentially deadly virus.
State health officials say there have been no confirmed cases of the virus in humans this year. There were a record 178 cases and 15 deaths in 2012.