Ask the Doctors

Dear Doctor: What is rat bite fever? Just how contagious or dangerous is it? I read that a 10-year-old boy died from it after being bitten by his pet rat.

Dear Reader: Yes, that was a tragic story. A rat purchased from a pet store transmitted a bacterial infection known as rat bite fever to a young boy who later died. Although the details caused the incident to get wide media play -- we tend to think of rats as vermin rather than pets -- the Centers for Disease Control and Prevention say that rat bite fever in the United States is quite rare.

Rats have been identified as carriers of disease for thousands of years. Rat scratches, urine and feces are all potential pathways for illness. Add in the various pests and parasites that live off rats and themselves spread disease -- think fleas and the bubonic plague, which killed 50 million people in Europe in the 14th century -- and it's no surprise that these rodents have earned a bad reputation.

So what is rat bite fever? It's a full-body illness with symptoms including fever, chills, body aches, headache and vomiting. In many patients, a rash made up of either flat or raised red bumps may appear a few days after the onset of fever. In the U.S., the cause of the disease is usually a bacterium called Streptobacillus moniliformis, which is transmitted through contact with the infected rat's saliva or urine. Spirillum minus, which also causes the disease, is more commonly found in Asia.

Although rats are the main carriers, the bacteria can be present in mice and gerbils as well. Rat bite fever is fatal in about 10 percent of infected persons who go untreated. In the case of that young boy, he may have been bitten by the rat, or may have become infected through handling his pet. As to your question about whether it's contagious, there have been no reports of rat bite fever being transmitted between humans.

The bacterium is present in healthy rats, both wild and domesticated. That means it's found in lab rats, too, which puts researchers at risk. But rat bite fever tends to be most common in urban areas, where rats can easily find food and shelter, and where residents have little control over coming into contact with the rodents or their urine.

Since a single test to diagnose the disease doesn't exist, the diagnosis must be made by identifying the presence of the bacteria in blood, skin or in the fluid of the joints of lymph nodes. However, prompt treatment is important, so the CDC recommends that patients who develop the cluster of symptoms associated with rat bite fever, particularly if they occur within two days to three weeks after contact with a rat, receive a course of antibiotics. Penicillin works extremely well, and for those who are allergic, other antibiotics are also effective.

We're very happy to be able to leave you with some good news: With timely treatment, the vast majority of patients with rat bite fever recover fully.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

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