Health officials are investigating how the Seoul virus infected eight people in Wisconsin and Illinois.
The Wisconsin Department of Health Services says these individuals had direct contact with rats at Illinois and Wisconsin rat breeding facilities.
Illinois Public Health Director Dr. Nirav Shah says the virus isn't a danger to the general public because of its limited ability to spread.
"In order for an individual to come down with Seoul virus, there actually needs to be pretty close, sustained contact with the rat," he said. "Seoul virus is transmitted not through the air, or from person to person, but through the urine and fecal matter of the rats."
Symptoms can include fever, chills, nausea, aches and pains or irritated skin.
Both people in Wisconsin recovered from the infections. Five of the six Illinois patients were asymptomatic.
State and federal health officials are investigating the source of the virus. None of the facilities involved are currently selling rats.