The Ohio Department of Agriculture is working with animal health experts to identify dog illnesses that have killed at least four pets on opposite ends of the state.
The outbreak has been reported near Cincinnati and Canal Fulton, located south of Akron in northeastern Ohio.
The agency's Division of Animal Health has been taking reports of severe dog illnesses for the past three weeks and at least four dogs have died.
Symptoms include vomiting, bloody diarrhea, weight loss and lethargy.
Agency spokeswoman Erica Hawkins says there are several known causes of the symptoms in dogs, but it's generally believed that there is an unknown contributor to the recent cases.
State pathologists have sent samples to a lab at the University of California-Davis for testing.
A one-year-old beagle with circovirus died in California in the spring, and the school's lab has the equipment to test for the virus, which had not previously been diagnosed in dogs but is common in pigs.
Dr. Melanie Butera, a veterinarian Canal Fulton, treated four dogs which were ill with similar symptoms. The two worst cases came in collapsed and weak, with high heart rates and fluid around their lungs.
"The dogs were so profoundly sick, over such a short period of time," she said, which is what set off alarm bells for her. One of the dogs, who survived the illness, was leaking fluid from his gums.
The statewide concern began around Aug. 16, when ODA urged owners to closely watch pets after several dog deaths were reported north of Cincinnati.