The West Nile virus has made its way across South Dakota.
Three additional cases of the virus were reported Friday, including a horse in Butte County near Belle Fourche.
Also a blue jay collected near Howard and a horse near Selby both tested positive for the virus, State Epidemiologist Lon Kightlinger said.
The virus was first detected in South Dakota more than a week ago in a crow found in Brown County.
It is transmitted through mosquito bites and mainly affects birds. Infected humans rarely become ill.
Kightlinger said people should take precautions to protect from mosquito bites by wearing repellant and getting rid of containers where water can collect and serve as mosquito breeding grounds.
Horse owners should get their animals vaccinated.
Mike Catangui, an Extension entomologist at South Dakota State University in Brookings, said the disease and mosquito control should be taken seriously.
The only way for humans to contract the disease is a bite from an infected mosquito, he said. Although there are no human cases of the virus in South Dakota, that could change, Catangui said.
"I think it is just a matter of time before we see the first human case," he said.
Mosquitoes in South Dakota will continue to carry the virus for years to come, so county mosquito spraying programs should be increased, he said.