October 2, 2022


Dear doctors: Can you please talk about rat bite fever? Our son was bitten by a baby rat while cleaning his garage, and he didn’t see a doctor. It turned out he was fine, but I worry about what could have happened. What should he have done?

Dear Reader: Close contact with wild rodents or the places where they live poses a health risk. Mice and rats can be infected with a range of bacteria and viruses, and they can transmit disease through their droppings, urine and saliva. Among these many illnesses is the one you are talking about: rat bite fever.

Rat bite fever is caused by two different bacteria. In the United States, the bacterium is called Streptobacillus moniliformis. In Asia, the disease is caused by a bacterium known as Spirillum minus. People can become infected if they are scratched or bitten by a rat. The bacterium can also be transmitted through food or water contaminated with waste from infected rodents. This causes a closely related disease known as Haverhill fever. In either case, the resulting disease can be serious, even fatal, if left untreated. Symptoms can begin as early as three days after contact with the bacteria. However, in some cases, it can take up to three weeks for symptoms to appear.

As the name of the disease suggests, it often begins with a fever. Other symptoms include headache, muscle aches, nausea, and vomiting. It is common for the fever to be followed after a few days by a rash on the hands or feet. About half of those infected also develop pain and swelling in one or more joints. Haverhill fever follows a similar pattern, but it often includes sore throat and swollen lymph nodes, as well as more severe vomiting.

When rodent contact and subsequent symptoms indicate rat-bite fever, the diagnosis is confirmed by culture of a sample of blood or joint fluid. Although immediate treatment with antibiotics is very effective in curing the disease, it is possible to experience persistent fatigue and joint pain.

It is when rat bite fever is left untreated that serious complications can occur. These include abscesses, which are pockets of infected fluid, often in the abdomen, and infections of major organs including the heart, liver, lungs and brain. About 10% of untreated cases result in death.

Any bite from a rodent, whether wild or domestic, should be taken seriously. As soon as possible, you should gently but thoroughly wash the area with soap and warm water. It is also important to consult a doctor. Rodent bites are puncture wounds and can easily become infected. You may be advised to get vaccinated against tetanus or possibly take a preventive course of antibiotics. Keep an eye out for the symptoms we’ve already discussed, as well as general signs of infection. This includes fever, redness or swelling at the site of injury, formation of pus, and skin that is warm to the touch. If any of these symptoms develop, seek medical attention immediately.

Eve Glazier, MD, MBA, is an internist and associate professor of medicine at UCLA Health. Elizabeth Ko, MD, is an internist and assistant professor of medicine at UCLA Health.

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