Rat-bite fever


Rat-bite fever refers to an infection which develops in a person after being bitten or scratched by an infected animal.


Rat-bite fever occurs most often among laboratory workers who handle lab rats in their jobs, and among people who live in poor conditions, with rodent infestation. Children are particularly likely to be bitten by rodents infesting their home and are, therefore, most likely to contract rat-bite fever. Other animals that can carry the types of bacteria responsible for this illness are mice, squirrels, weasels, dogs, and cats. One kind of bacteria can cause the same illness if it is ingested in unpasteurized milk or in water that has been contaminated with rat waste.


About half of all cases of rat-bite fever occur in children.

Causes and symptoms

There are two variations of rat-bite fever, caused by two different organisms. In the United States, the bacteria Streptobacillus moniliformis is the most common cause (causing streptobacillary rat-bite fever). In other countries, especially Africa, Spirillum minus causes a different form of the infection (called spirillary rat-bite fever).

Streptobacillary rat-bite fever occurs up to 22 days after the initial bite or scratch. The patient becomes ill with fever, chills, nausea and vomiting , headache , and pain in the back and joints. A rash made up of tiny pink bumps develops, covering the palms of the hands and the soles of the feet. Without treatment, the patient is at risk of developing serious infections of the lining of the heart (endocarditis), the sac containing the heart (pericarditis), the coverings of the brain and spinal cord ( meningitis ), or lungs ( pneumonia ). Any tissue or organ throughout the body may develop a pocket of infection and pus, called an abscess.

Spirillary rat-bite fever occurs some time after the initial injury has already healed, up to about 28 days after the bite or scratch. Although the wound had appeared completely healed, it suddenly grows red and swollen again. Lymph nodes in the area become swollen and tender, and the patient develops fever, chills, and headache. The skin in the area of the original wound sloughs off. Although rash is less common than with streptobacillary rat-bite fever, there may be a lightly rosy, itchy rash all over the body. Joint and muscle pain rarely occur. If left untreated, the fever usually subsides, only to return again in repeated two- to four-day cycles. Though these cycles can last for a year, the illness usually resolves without treatment in four to eight weeks. This can go on for up to a year although, even without treatment, the illness usually resolves within four to eight weeks.


In streptobacillary rat-bite fever diagnosis can be made by taking a sample of blood or fluid from a painful joint, which can be cultured to allow the growth of organisms. Examination under a microscope will then allow identification of the bacteria Streptobacillus moniliformis .

In spirillary rat-bite fever, diagnosis can be made by examining blood or a sample of tissue from the wound for evidence of Spirillum minus .


Either injections of procaine penicillin G or penicillin V by mouth are effective against both streptobacillary and spirillary rat-bite fever. When a patient is allergic to the penicillins , either erythromycin may be given by mouth for streptobacillary infection or tetracycline by mouth for spirillary infection.


With treatment, prognosis is excellent for both types of rat-bite fever. Without treatment, the spirillary form usually resolves on its own, although it may take up to a year to do so.

The streptobacillary form, found in the United States, however, can progress to cause extremely serious, potentially fatal complications. In fact, before antibiotics were available to treat the infection, streptobacillary rat-bite fever frequently resulted in death.


Prevention involves avoiding contact with those animals capable of passing on the causative organisms. This can be a difficult task for people whose economic situations do not allow them to move out of rat-infested buildings. Because streptobacillary rat-bite fever can occur after drinking contaminated milk or water, only pasteurized milk, and water from safe sources, should be ingested.

Parental concerns

The parents of children living in rodent-infested conditions, or who have pet rodents (mice, rats, gerbils) should be vigilant to illness in their children.


Abscess —A localized collection of pus in the skin or other body tissue caused by infection.

Endocarditis —Inflammation of the inner membrane lining heart and/or of the heart valves caused by infection.

Meningitis —An infection or inflammation of the membranes that cover the brain and spinal cord. It is usually caused by bacteria or a virus.

Pasteurization —A process during which milk is heated and maintained at a particular temperature for the purpose of killing, or retarding the development of, pathogenic bacteria.

Pericarditis —Inflammation of the pericardium, the sac that surrounds the heart and the roots of the great blood vessels.



Barnett, S. Anthony. The Story of Rats: Their Impact on Us and Our Impact on Them. Crows Nest, New South Wales, Australia: Allen & Unwin, Pty., Limited, 2002.

Conniff, Richard. Rats: The Good, the Bad, and the Ugly. New York: Random House Children's Books, 2002.

Sullivan, Robert. Rats: Observation on the History and Habitat of the City's Most Unwanted Inhabitant. London: Bloomsbury Publishing, 2005.


Centers for Disease Control and Prevention. 1600 Clifton Rd., NE, Atlanta, GA 30333. Web site: http://www.cdc.gov.


"Rat-bite fever." MedlinePlus. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/001348.htm (accessed December 29, 2004).

Rosalyn Carson-DeWitt, MD

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