A Michigan veterinarian says she thinks the mysterious dog illness that has killed at least four dogs in Ohio so far may be transferred to and from humans.

Last month, the Ohio Department of Agriculture said its Division of Animal Health had been taking reports of sick dogs and investigating.

Symptoms of the mysterious illness include vomiting, bloody diarrhea, weight loss and lethargy.

The dogs believed to have died from the illness were in the Cincinnati and the Akron areas.

Dr. Lindsay Ruland is with the Emergency Veterinary Hospital in Ann Arbor, Michigan. Ruland tells NBC4 she began seeing dozens of cases of the mysterious dog illness last year.

Ruland says this year she has seen even more cases and has also noticed a correlation between the owners of her patients who have reported flu-like symptoms around the same time as their dog's illness.

Additionally, many employees at Emergency Veterinary Hospital also became sick after coming into contact with dogs who were ill.

Ruland says she reached out to state health officials last year as well as the Centers for Disease Control to alert them to her concerns.

However, Ruland also emphasizes that more scientific research must be done.

Erica Hawkins with the Ohio Department of Agriculture said Thursday that the agency had not heard about Ruland's concern until Thursday, but ODA does not believe the mysterious dog illness is connected to humans.

A spokesperson with the Michigan Department of Agriculture and Rural Development also told NBC4 the agency did not currently believe the illness was transferred between humans and animals.

According to the CDC's website, "Zoonotic diseases are contagious diseases spread between animals and humans. These diseases are caused by bacteria, viruses, parasites, and fungi that are carried by animals and insects."

According to the CDC, examples include Lyme disease and Rocky Mountain spotted fever.