People who handle rats in labs or keep them as pets are at risk of contracting a rare but potentially deadly disease called rat-bite fever, U.S. health officials said on Thursday.

The Centers for Disease Control and Prevention issued the warning following a probe into the 2003 deaths of two previously healthy women in Florida and Washington state.

Both died of rat-bite fever within 12 hours of being hospitalized, according to a report released by the CDC. One had been bitten by a rat at the pet store in which she worked.

The other owned nine pet rats, none of which appeared to have bitten her.

“These are unique cases,” said Sarah Reagan, a CDC epidemiologist, who noted that the few cases known to have occurred among adults in the United States had involved longer, complicated illnesses.

Rat-bite fever is caused by Streptobacillus moniliformis, an organism found in the upper respiratory tracts of rats. Symptoms include fever, rash, vomiting and muscle aches.

Although usually curable with intravenous doses of penicillin or oral antibiotics, the disease has a 7 percent to 10 percent case fatality rate when prompt medical treatment is not sought.

It is not necessary to be bitten or scratched by a rat to contract the disease. People who have ingested rat urine or droppings while cleaning rodent cages or eating contaminated food also can become infected.

The CDC urged people to wear gloves, wash their hands frequently and avoid hand-to-mouth contact when handling rats or cleaning rat cages. Anyone bitten by a rat should clean and disinfect the wound and seek medical treatment.