Rat Bite Fever

Rat bite fever

Description, Causes and Risk Factors:

Rat bite fever is a rare disease in the U.S. caused primarily by the bacterium Streptobacillus moniliformis. In some other parts of the world, particularly Asia, another bacterium called Spirillum minus commonly causes spirillary rat bite fever. Rats can carry the bacteria that cause this disease and generally do not show any signs of illness. Disease, sometimes fatal, can occur in humans and a variety of animal species.

Rat bite fever is casued by spirillum minus and streptobacillus moniliformis bacteria. It is transmitter to humans through contact with secretions or blood of an infected rodent. Rats are the most common carrier of the bacteria. Squirrels, gerbils, and other carnivores that prey on rodents can also carry the disease. The bacteria is transferred in approximately 10% of bites to humans. Both forms of bacteria primarily affect urban dwellers that live in crowded conditions. In the United States and Europe, most cases are caused by streptobacillus moniliformis and can be known as Haverhill fever or epidemic arthritic erythema. In Asia it is commonly caused by spirillum minus and is known as sodoku or spirillosis. These bacteria are spiral shaped and are not found in clusters. They are characterized by their shape, size of spirals, number of spirals and the direction of the spirals.

Rat bite fever is spread to animals by direct contact (usually bites and scratches) with infected rats. It can also be spread by ingestion (oral) of infected rats or food or water contaimanted with rat feces or urine.

Human infection is usually acquired either from a rat bite/scratch, handling infected rats, or, in the case of the form of disease known as Haverhill fever, ingestion of milk or water contaminated with the organism (via rat urine). A large outbreak occurred following this route of transmission in the UK in 1983. At a boarding school in Essex, 304 pupils (of 700, 43%) had a febrile illness with arthralgia and a rash. Four cases were blood culture positive for S. moniliformis. Raw milk initially appeared to be the vehicle of infection, but detailed epidemiological investigations and analysis showed that the vehicle was more likely to have been water. Opportunity for contamination of drinking water by rats existed, although contamination was not confirmed by the isolation of S. moniliformis from either rats or the water supply.

Risk Factors:

Any person who is exposed to the bacteria that cause RBF is at risk for getting the disease. Some people who may be at increased risk include those who:

    Live in rat-infested buildings.

  • Have pet rats at their home.

  • Work with rats in laboratories or pet stores.


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 (e.g., 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 (e.g., infection of the heart, pneumonia, meningitis, hepatitis).


Diagnosis is confirmed by culturing blood or fluid joint and locating the bacteria. It can also be visually diagnosed or blood tests can be performed. Rat bite treatment should be administered quickly after contact. After bleeding is controlled, the wound should be washed inside and out with warm water and soap to kill the bacteria. After the wound is dry, applying antibiotic ointment under a dressing is recommended. Most rodent bites are deep and could require stitching to help close the wound and keep the risk of infection down. Physicians will prescribed oral penicillin for rat bite treatment. A penicillin injection is given by the physician and oral tablets or suspension are prescribed for at home use over a course of 10 to 14 days. Persons that are allergic to this medication can use other antibiotics in its place. Other medicines can be prescribed to reduce the symptoms associated with the bite.


If you have any symptoms of rat-bite fever after exposure to rats or other rodents, please immediately contact your health care provider. Be sure to tell your provider of your exposure to rodents.

If you have RBF, your doctor can give you antibiotics that are highly effective at curing the disease. Penicillin is the antibiotic most often used. If you are allergic to penicillin, your doctor can give you other antibiotics.

Without treatment, RBF can be serious or potentially fatal. Severe illnesses can include:

    Infections involving the heart (endocarditis, myocarditis, or pericarditis).

  • Infections involving the brain (meningitis).

  • Infections involving the lungs (pneumonia).

  • Abscesses in internal organs.

While death from RBF is rare, it can occur if it goes untreated.

Avoiding contact with rodents is the most effective prevention for these conditions. Depending on geographical location, one of two types of spirillum bacteria can cause the infection. Treating an open sore or bite quickly and seeking medical attention for immediate treatment is necessary to reduce the risk of death due to rat bite fever.

NOTE: The above information is for processing purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.

DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.


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