Rat Bite Fever, Streptobacillus moniliformis

More than 2 million animal bites occur each year in the United States, and rats are responsible for approximately 1% of these. Historically, the typical victim of rat bite fever was a child under 5 years old living in poverty, and over 50% of reported cases in the United States were children. Now that rats have become popular pets and study animals, the demographics of potential victims have broadened to include children under 12 years, pet store workers, and laboratory technicians. 6 A report from the Centers for Disease Control and Prevention in 2005 describing two rapidly fatal cases of rat-bite fever in previously healthy adults illustrates that rat-bite fever is still an important zoonotic infection after occupational and recreational exposure to rats, and S. moniliformis-related infections may be re-emerging.

Disease following the bite of a rat has been known in India for over 2,300 years, but it has been described worldwide much more recently as rat bite fever. This term describes two similar yet distinct disease syndromes caused by Streptobacillus moniliformis or Spirillum minus. Rat bite fever caused by S. moniliformis is more common in North America, while S. minus infection, also known as sodoku, is more common in Asia. Streptobacillus moniliformis bacteria colonizes the upper respiratory tract of 10% to 100% of healthy domesticated or laboratory rats, and 50% to 100% of wild rats. Rats are the natural reservoir of the bacteria, but gerbils, mice, and other rodents are also carriers.

Streptobacillus moniliformis was previously known as Haverhilia multiformis, named after the epidemic of rat bite fever that occurred in Haverhill, Massachusetts in 1926. 9

Although many cases of rat bite fever follow rat bites, rat bites are not always reported, and multiple infections have been reported from scratches, kissing pet rodents, and even the ingestion of pets' feces. Exposure to other domestic and wild animals has also resulted in disease. Infection has also followed consumption of contaminated raw milk and water.5,4,11 Rat bite fever is not transmitted person-to-person.

Clinical Signs

The clinical features of this syndrome typically appear one to two weeks after the initial bite. Patients report an initial asymptomatic period followed by fever (in 50% of cases), chills, nausea and headache. Many people also develop muscle and joint pain. A rash with or without pus may form on the soles of the feet or palms of the hands of affected individuals. Reported complications of the disease in humans have included bacterial endocarditis, brain abscesses, joint inflammation, pericarditis, myocarditis, hepatitis, nephritis, meningitis, pneumonia, sepsis, and other organ abscesses. Children and infants may develop severe diarrhea. When it is caused by ingestion of contaminated food/drink (Haverhill fever), severe nausea, vomiting, and inflammation of the throat typically occur. 14 The risk of infection after a rat bite appears to be 10%. The mortalityt rate is about 13% if untreated. 9,6,7

Diagnosis & Treatment

Diagnosis is made by blood culture, cultivation from pus from the bite wound, or from synovial fluid. S. moniliformis is characterised by strict growth requirements and slow growth, making it difficult to culture. S. moniliformis is susceptible to penicillin. In uncomplicated cases, recommended treatment is oral penicillin or intravenous penicillin for 10–14 days. Reported cases of septic arthritis have been treated with intravenous penicillin for a duration of 10 days to six weeks. The addition of streptomycin has been advocated to enhance activity against the pathogen. Erythromycin, chloramphenicol, clindamycin, cephalosporins, and ciprofloxacin have been tried with variable success. 12


Working in farms, barns, warehouses and pet shops are all associated with possible rat exposure even if the victims cannot recall any rat bite or scratch. There is also a possibility of rat exposure during recreational activities such as travelling to villages and the countryside. Only drink pasteurized milk and water from safe sources. When handling rats: wear protective gloves, wash hands thoroughly and regularly, and avoid touching mouth with hands. Control wild rat populations around homes. Store food/water properly to prevent contamination by rodents. If a bite should occur, clean and disinfect it promptly. Seeking medical attention is recommended and post-exposure penicillin may be administered, as rat bite fever occurs in 10% of rat bites. 10,12

Rat Bite Fever


  1. Streptobacillus moniliformis septic arthritis: a clinical entity distinct from rat-bite fever?
  2. The rise of the rats: A growing paediatric issue
  3. Rat bite fever, a fatal case of Streptobacillus moniliformis infection in a 14-month-old boy.
  4. Epidemiologic Notes and Reports Rat-Bite Fever in a College Student--California
  5. Rat bite fever and Streptobacillus moniliformis
  6. Rat Bite Fever and Streptobacillus moniliformis
  7. Clinical, Microbiological, and Histological Manifestations of Streptobacillus moniliformis-Induced Arthritis in Mice
  8. Rat bite fever
  9. Fever and a rat bite
  10. Streptobacillus moniliformis septic arthritis: a clinical entity distinct from rat-bite fever?
  11. Suppurative polyarthritis following a rat bite

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