LANSING, Mich. — Last week the Michigan Department of Agriculture and Rural Development (MDARD) announced two new cases of Eastern equine encephalitis (EEE) in horses in southwestern Lower Michigan.

One of the cases was in Calhoun County, the other in Van Buren County. According to the announcement Sept. 28, the USDA’s National Veterinary Services Lab in Ames, Iowa, notified MDARD of the results on Sept. 22. Both horses tested positive for EEE exposure and had already been euthanized.

Mosquitoes carry the deadly virus, which is transmitted from them to horses, people, birds and some other mammals, including dogs. Horses can’t transmit the virus to people or to one other.

"In all three cases the horses were not vaccinated," said Dr. James Averill, the state veterinarian.

The third case, announced earlier in September, was discovered in Barry County, also in southwestern Lower Michigan. A veterinarian in private practice who sent the blood sample to the lab in Ames did the initial testing.

"What this demonstrates is that the virus is there in the mosquito population," Averill said. "There are very effective vaccines available."

He said there might be more cases of EEE until the area sees a "good, hard frost." Although Michigan is nearing the end of the mosquito season, it’s not unusual to see EEE persist into October, depending on the vagaries of the weather. Although often there is a hard frost in October, it’s also not unusual to see a warm-up during this month as well.

Normally the time to get a horse vaccinated for EEE is in the spring when mosquitoes first emerge. At this point it wouldn’t be worth it to have a horse vaccinated, unless the horse is taken South for the fall, which isn’t unusual, Averill said.

When asked about the possibility a horse might need to be vaccinated twice in a season, he didn’t want to comment on that. "All we can really recommend is that people work with their local veterinarian on a vaccination schedule," he said. "The vaccines cost more than $1 apiece, but they are a whole lot cheaper than if your horse dies."

Other than the vaccine, state officials recommend the same prevention strategies for EEE as they do for West Nile virus. People should use mosquito repellent, wear protective clothing and eliminate standing water on their property, such as in unused tires. Horses and pets should be indoors from early evening until after sunrise, when mosquitoes are out in full force. Fans are recommended to keep the mosquitoes away from horses at night.

EEE is also known as horse sleeping sickness. It’s a highly fatal virus that affects the nervous system and is spread among wild birds by mosquitoes. In horses, EEE can cause severe swelling of the brain, stumbling, depression and sometimes blindness.

Veterinarians who work with horses showing signs of EEE are asked to call MDARD at 517-284-5767. EEE is a reportable disease in both humans and animals. Doctors who suspect a human case are asked to call their local health department.

Anyone who suspects an animal has EEE is asked to report it to MDARD by calling 800-292-3939.