Rat-bite fever

Rat-bite fever can be caused by either of two different bacteria, Streptobacillus moniliformis or Spirillum minus. Both of these are found in the mouths of rodents.

The disease is most often seen in:

• Asia
• Europe
• North America

Most people get rat-bite fever through contact with urine or fluids from the mouth, eye, or nose of an infected animal. This most commonly occurs through a bite or scratch. Some cases may occur simply through contact with these fluids.

A rat is usually the source of the infection. Other animals that may cause this infection include:

• Gerbils
• Squirrels
• Weasels

Symptoms depend on the bacteria that caused the infection.

Symptoms due to Streptobacillus moniliformis may include:

• Chills
• Fever
• Joint pain, redness, or swelling
• Rash

Symptoms due to Spirillum minus may include:

• Chills
• Fever
• Open sore at the site of the bite
• Rash with red or purple patches and bumps
• Swollen lymph nodes near the bite

Symptoms from either organism usually resolve within 2 weeks. Untreated, the symptoms, such as fever or joint pain, can keep returning for many weeks or longer.

The health care provider will perform a physical examination and ask about your symptoms. If the provider suspects rat bite fever, tests will be done to detect the bacteria in:

• Skin
• Blood
• Joint fluid
• Lymph nodes

Blood antibody tests and other techniques may also be used.

Rat-bite fever is treated with antibiotics (typically oral) for 7 to 14 days.

The outlook is excellent with early treatment. If it is not treated, the death rate can be as high as 25%.

Rat-bite fever may cause these complications:

• Abscesses of the brain or soft tissue
• Infection of the heart valves
• Inflammation of the parotid (salivary) glands
• Inflammation of the tendons
• Inflammation of the heart lining

Contact your provider if:

• You or your child has had recent contact with a rat or other rodent
• The person who was bitten has symptoms of rat-bite fever

Avoiding contact with rats or rat-contaminated dwellings may help prevent rat-bite fever. Taking antibiotics by mouth promptly after a rat bite may also help prevent this illness.

Streptobacillary fever; Streptobacillosis; Haverhill fever; Epidemic arthritic erythema; Spirillary fever; Sodoku

Mekala V, Washburn RG. Rat-bite fever: Streptobacillus moniliformis and Spirillum minus. In: Bennett JE, Dolin R, Blaser MJ, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 9th ed. Philadelphia, PA: Elsevier; 2020:chap 231.

Shandro JR, Jauregui JM. Wilderness-acquired zoonoses. In: Auerbach PS, Cushing TA, Harris NS, eds. Auerbach's Wilderness Medicine. 7th ed. Philadelphia, PA: Elsevier; 2017:chap 34.

Vyas JM. Rat-bite fever. In: Kellerman RD, Rakel D, Heidelbaugh JJ, Lee EM, eds. Conn's Current Therapy 2023. Philadelphia, PA: Elsevier; 2023:670-672.

Updated by: Jatin M. Vyas, MD, PhD, Associate Professor in Medicine, Harvard Medical School; Associate in Medicine, Division of Infectious Disease, Department of Medicine, Massachusetts General Hospital, Boston, MA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.