LOUISVILLE_ An insect-borne virus that has taken a toll on deer has spread to some cattle herds, presenting another problem for producers already struggling with a shortage of feed supplies, authorities said.

Wade Northington, director of an animal diagnostic laboratory in western Kentucky, said yesterday that epizootic hemorrhagic disease, or EHD, was detected by his lab in 20 to 30 cattle that died in recent weeks.

“A lot of people are very, very concerned,” said agricultural extension agent Rick Greenwell in Washington County, where the virus is blamed for infecting some herds and killing several cattle.

The disease, which cannot be contracted by humans, is spread to deer or cattle by gnats or flies. Horses do not appear to be susceptible to the virus, said Mr. Northington, director of the Murray State University Breathitt Veterinary Center in Hopkinsville.

Mature cattle generally survive the virus but can be sick for a week to 10 days. Symptoms include fever, diarrhea, nose or mouth lesions and stiffness.

There is no vaccine to prevent the illness, Mr. Northington said.

“It’s kind of like having the flu, you just have to wear it out,” he said.

Veterinarians suspect that some cases of aborted calves may also be due to the disease, he said.

The virus is another headache for cattle farmers in Kentucky, the largest beef cattle producer east of the Mississippi. Cattle accounted for 14 percent of

Kentucky agricultural sales in 2005, putting it behind only horses and poultry as the biggest farm sectors, according to figures from the state Agriculture Department.

Kentucky cattle producers have already been struggling with inadequate hay supplies and pastures since a spring freeze followed by a summer drought.

That has many worrying how they will feed herds this winter.

Now, some farmers are dealing with sick cattle: “It’s just another aggravation for them,” said Greensburg veterinarian Michael Shuffett.

Dr. Shuffett said that in south-central Kentucky, treating cattle infected by the virus, or suspected of having it, has become a daily occurrence at his practice in the past six weeks. “We’ve treated an average of two cows a day, sometimes four or five a day,” he said.

Cattle producers can try to protect their herds through insect-control measures, Shuffett said.

The disease is blamed for killing at least 1,100 to 1,200 deer so far, about 1 percent of the state’s total herd, said Mark Marraccini, spokesman for the Kentucky Department of Fish and Wildlife Resources.

The outbreak in deer is probably the worst in 30 years, he said, because the drought forced herds to congregate at remaining water sources, making it easier for the gnats or flies to infect them.

Green County cattle farmer David Lee Givens learned that the illness can strike quickly. In one of his herds, five cows died during a two-day period earlier this month.

“You’ve just got to tighten your belt up, replace those cows with other heifers and keep the thing rolling.”