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Spirillum minus rat-bite fever
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Spirillum minus rat-bite fever

Contributors: Vivian Wong MD, PhD, Susan Burgin MD, David L. McCollum MD, J. Martin Rodriguez MD, James H. Willig MD, MSPH
Other Resources UpToDate PubMed


Rat-bite fever (RBF) is a febrile illness resulting from infection with either Streptobacillus moniliformis or Spirillum minus. The causative agent of the more common RBF is S moniliformis, which is found worldwide. RBF due to S minus is found primarily in Asia. Alternative terms for this form of RBF include spirillary fever and the Japanese name sodoku (from so meaning rat and doku meaning poison). RBF due to S minus rarely occurs in the United States but has occurred in laboratory workers. Travelers to endemic areas are also at risk.

Spirillum minus is a gram-negative, spiral-shaped rod that cannot be grown on artificial media. It has been found in up to 25% of wild rats (in oropharynx, blood, or eye exudate). It is much less common in laboratory rats.

RBF due to S minus arises from the bite of a rat. At highest risk for RBF are persons with exposure to rats including laboratory workers, undomiciled persons, and children with rats as pets.

RBF due to S minus typically presents with the following sequence:
  • The initial rat bite heals.
  • One to four weeks later, the bite site becomes edematous and tender. Regional lymphangitis appears. A systemic febrile illness occurs. Arthritis is typically absent. Infants and children may develop severe diarrhea and weight loss. The systemic symptoms may be accompanied by a diffuse macular rash.
  • The bite site then ulcerates and may form an eschar. Laboratory examination may show leukocytosis.
Without antimicrobial therapy, the illness may become relapsing. The pattern is typically a recurrent pattern of 3 days of fever followed by a 3- to 9-day afebrile period.

If untreated, potential complications of both forms of RBF may include meningitis, endocarditis, myocarditis, hepatitis, nephritis, and splenomegaly.


A25.0 – Spirillosis

19044004 – Spirillary fever

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Differential Diagnosis & Pitfalls

  • RBF due to Streptobacillus moniliformis rat-bite fever – Often associated with a petechial rash and polyarthritis.
  • Cat-scratch disease due to Bartonella henselae
  • Sporotrichosis – Commonly presents as a lymphocutaneous syndrome after exposure to soil or vegetation (landscapers, etc).
  • Cutaneous nocardiosis – May also present as a lymphocutaneous syndrome termed "sporotrichoid nocardiosis."
  • Tularemia – Of the 6 major clinical forms of tularemia, the ulceroglandular form may most closely mimic RBF due to S minus.
  • Mycobacterial infection – Both Tuberculosis and Atypical mycobacterial infection (especially Mycobacterium marinum infection) can present with nodular lymphangitis.
  • Cutaneous leishmaniasis – Cutaneous lesion (papule, nodule, or ulcer) can be associated with lymphangitis or lymphadenopathy.
  • Sexually transmitted diseases including Primary syphilis, Lymphogranuloma venereum, and Chancroid
  • Streptococcal or staphylococcal lymphadenitis
  • Herpes simplex virus (HSV) – Primary HSV infection can be associated with lymphadenopathy.
  • Anthrax – Cutaneous anthrax may be associated with an ulcer and lymphangitis.
  • Plague – Of the 3 major clinical forms of plague, the Bubonic plague may most closely mimic RBF due to S minus.
  • Leptospirosis – Systemic febrile illness associated with exposure to rats and other animals. It presents with variable severity ranging from mild disease to multiorgan failure.

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Last Reviewed:10/17/2018
Last Updated:07/18/2023
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Spirillum minus rat-bite fever
A medical illustration showing key findings of Spirillum minus rat-bite fever : Chills, Fever, Eschar, Leukocytosis, Malaise, Regional lymphadenopathy, Rat bite
Copyright © 2024 VisualDx®. All rights reserved.