One horse has been diagnosed with West Nile virus and another has symptoms highly suspicious of the virus transmitted by mosquitos. People are also at risk for the disease.

A press release from Flathead City-County Health Department warned people to protect themselves from possible infection with repellent and protective clothing until a hard frost ends the mosquito season.

Veterinarian John Erfle of the LaSalle Equine Clinic said that one horse was located in Lakeside and the other was in Columbia Falls. Neither horse had been vaccinated against the disease. There is no vaccine for humans for West Nile virus.

According to Erfle, about 70 percent of horses infected have no symptoms. He said about a third of the 30 percent of horses who develop symptoms die from the virus.

"Many of those lost could survive if horses could be down for a period of time," Erfle said.

The vet said horse can't survive more than 24 hours down. He said the diagnosed horse is recovering from the virus.

He said some other equine cases were reported two weeks ago in the Ronan area. With horses now sickened in the Flathead, Erfle called it "the canary in the mine" or a warning for other horse owners as well as the general public.

"It's here," he said. "I think it's a good warning to be cautious and avoid mosquito bites this time of year."

Erfle said it's probably too late to vaccinate horses that haven't had the vaccine in previous years. However, horses that had the vaccine before still have time for a booster that can take effect in two to six weeks.

His clinic sells the vaccine for $17.50 to owners to vaccinate their own horses. The additional cost is for the clinic to administer the shot.

"It's an important disease in horses," Erfle said. "People need to take notice and take precautions."

About 80 percent of humans infected have no symptoms while 20 percent have flu-like symptoms such as fever, headache and tiredness. Occasionally, a person has a rash on the trunk of the body, eye pain and swollen lymph glands.

One percent of infected people develop a severe neurological form of infection in the brain or spinal cord called meningitis or encephalitis. Severe symptoms requiring immediate medical attention include high fever, confusion, muscle weakness or severe headache.

Fatalities of those with severe forms average three percent.

Reporter Candace Chase may be reached at 758-4436 or by e-mail at cchase@dailyinterlake.com.