Four dogs have died from a mysterious illness in Ohio, prompting state agriculture officials to issue a warning.

"Affected dogs have exhibited similar symptoms including vomiting, bloody diarrhea, weight loss and lethargy," the Ohio Department of Agriculture said in the warning. "Although there are several known causes of these symptoms in dogs, it is generally believed that there is an unknown contributor to the cases."

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Three dogs that stayed at the same kennel in Cincinnati got sick and died about a month ago, Ohio Department of Agriculture spokeswoman Erica Hawkins told ABCnews.com. Another dog died of a similar illness two weeks ago in Akron, and a veterinarian there said she treated other dogs with the same symptoms who survived.

Although it looks like two clusters of the same illness, labs have not yet been able to confirm what killed the dogs or whether it was the same in both clusters, Hawkins said.

Fecal samples taken from one of the dogs contained canine circovirus, a newly identified virus about which very little is known. A spokesman for the Ohio Department of Agriculture told ABCNews.com that only one lab in the country studies the virus, and it is in San Diego.

Canine circovirus can cause hemorrhaging and inflammation of the blood vessels but may not have been the cause of death, according to the department's statement.

Concerned pet owners and veterinarians have called the department over the past several weeks.

"We want to share good information with owners who are concerned about their animals," she said. "But it's hard to do that when we don't have a lot of answers."

Hawkins said no new cases have been identified in the last two weeks.