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Rat Bite Fever

Rat-bite fever is a disease that occurs in humans who have been bitten by an infected rat or, in some cases, squirrels, mice, cats, and weasels. On occasion, the disease can also be spread by ingestion of contaminated food or milk products (Haverhill fever). Most cases in the United States are caused by bacteria called Streptobacillus moniliformis. Another form of rat-bite fever, caused by Spirillum minus, is almost always caused by a rat bite. It cannot be caught from food or milk and is rarely seen in the United States. Person-to-person transmission does not occur. The incubation period is 3 to 10 days in most cases of S moniliformis and 7 to 21 days in cases of S minus.

Signs and Symptoms

Rat-bite fever symptoms can vary depending on which organism is responsible for the disease. When the disease is caused by S moniliformis, the bite, which usually heals quickly, is followed 3 to 10 days later by:

  • Fever and chills
  • Headache
  • Skin rash (mostly on the arms and leg )
  • Muscle pain
  • Arthritis (particularly in the knees)
  • Vomiting and diarrhea
  • Complications (eg, abscesses, pneumonia, meningitis, heart inflammation)

With infections caused by S minus, the site of the bite may appear to heal initially, but 7 to 21 days later, the following symptoms may surface:

  • Fever and chills
  • Headache
  • Ulceration at the site of the bite with red streaks
  • Swelling of the lymph nodes
  • A skin rash with reddish-brown or purple plaques
  • Muscle pain and arthritis (rare)
  • Vomiting and sore throat (Haverhill fever)
  • Complications (eg, infection of the heart, pneumonia, meningitis, hepatitis)

Both forms of rat-bite fever may result in recurrent fevers, sometimes for months or years.

How Is the Diagnosis Made?

Your pediatrician can conduct tests such as cultures or smears of the blood or fluids from the site of the infection (eg, bite, lymph glands, joints) to find the bacteria responsible for rat-bite fever.


To treat rat-bite fever, the doctor will give your child penicillin G by injection or intravenously for 7 to 10 days. Alternative drugs include ampicillin, cefuroxime, and cefotaxime.

What Is the Prognosis?

With prompt treatment, most children with rat-bite fever recover completely.


Any animal bite should be cleaned well with soap and water. Treatment for 2 or 3 days with amoxicillin clavulanate by mouth may be helpful in preventing infection. The need for a tetanus vaccine should be reviewed.

Last Updated
Immunizations & Infectious Diseases: An Informed Parent's Guide (Copyright © 2006 American Academy of Pediatrics)
The information contained on this Web site should not be used as a substitute for the medical care and advice of your pediatrician. There may be variations in treatment that your pediatrician may recommend based on individual facts and circumstances.
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