Rat-Bite Fever

Rat-bite fever is a rare, infectious, non contagious, yet life threatening ailment that can occur due to two different types of bacteria.

There are two types of this disease:

  • Streptobacillus moniliformin causes streptobacillary RBF that is prevalent in North America.
  • Spirillum minus cause spirillary RBF that is found more in Asia. It is also called sodoku.

Another variant of Rat-bite fever disease is Haverhill fever, so named after the town in USA where there was an outbreak in 1920.


The two specific forms of bacteria are mostly transmitted through getting bitten by infected rodents, or coming in contact with their wastes. Another risk factor is consumption of food and drink that is contaminated with the bacteria.

Other than rats and mice, animals responsible for spreading the disease may include infected weasels, gerbils, ferrets, guinea pigs, hamster, squirrels, and household pets like cats or dogs.

Signs and symptoms

The incubation period, or the span between getting infected by the bacteria and the appearance of the first symptom is usually less than 7 days, but may range from 3 days to 3 weeks:

Young woman with thermometer in mouth having Rat-Bite Fever
Young woman with thermometer in mouth having fever

Streptobacillary RBF symptoms

Symptoms occur 3-10 days after infection

  • Sudden high fever and chills
  • Nausea and vomiting
  • Muscle pain
  • Severe headache
  • Sore throat
  • Flat reddened areas with persistent small bumps or rashes on arms and legs (indicating a maculopapular rash)

If not treated on time, pain and swelling in the ankle, fingers, hands, heels and joints can lead to arthritis and polyarthralgia in the long term.

Spirillary RBF symptoms

Symptoms occur 7-21 days after infection

  • Relapsing fever
  • Swelling of the lymph nodes
  • Swelling around the bite
  • Rashes with red or purple patches (occurring after partial healing of the bite)
  • An open sore or ulcer at the site of the bite
  • Rectal pain (in rare cases)

Haverhill fever is often associated with more severe fever, nausea and headache.

Diagnosis and tests

A physical examination of the skin or lymph nodes is undertaken to detect the bacteria. Blood tests and fluid cultures are done to detect the bacteria for both forms of the disease.

Differential diagnosis

  1. Sepsis
  2. Lyme disease
  3. Brucellosis
  4. Rickettsial infection including Rocky Mountain spotted fever
  5. Leptospirosis
  6. Secondary Syphilis
  7. Virus infections including Epstein- Barr Virus
  8. Malaria and typhoid
  9. Collagen vascular disease
  10. Drug reactions


In case of late treatment, Rat-bite fever disease may turn severe and affect some organs and body systems. Complications of the brain:

  • Encephalitis
  • Abscesses of the brain
  • Meningitis

Complications of the heart:

  • Endocarditis
  • Pericarditis
  • Myocarditis
  • Systemic vasculitis

Complications related to the lungs:

  • Pneumonia
  • Bronchitis

Treatment and management

The ailment is curable with antibiotic treatment, with penicillin being the most commonly used medication. Additionally an antibiotic ointment can be applied when the wound is dry. For deep bites, stitching may be needed as it helps in closing the wound and preventing the spread of infection. Those allergic to penicillin may be prescribed some other similar antibiotics, like tetracyclines.

Even in pregnant women, penicillin is the safe treatment method with no reported cases of any transplacental infection.

How to prevent rat bite fever

Since at present no vaccines are available to prevent this disease, it is better to observe the following precautions:

  • In case of a rodent bite, the wound should be cleaned thoroughly with soap and warm water as soon as the bleeding is under control, to kill any harmful bacteria.
  • Pasteurized milk or water should be drunk from safe sources.
  • Those likely to come in contact with rodents or their wastes, like animal handlers, lab employees, sanitation and sewerage workers, should wear protective gloves while handling rodents, and wash their hands with disinfectant soaps


The recovery rate is high, as the symptoms go away within a few days with proper treatment. However, there can also be an incidence of a host of complications if left without treatment. It is associated with a mortality rate of approximately 7 to 10% when left untreated.

Prevalence: How common is rat-bite fever

Over 20,000 rat bites are reported each year on average in the US, with only about 10% of them being at risk of advancing to the life threatening condition, without proper care.


  1. http://www.cdc.gov
  2. http://www.uptodate.com
  3. http://patient.info
  4. https://www.merckmanuals.com

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