Spirillum minus rat-bite fever
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Synopsis
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.
If untreated, potential complications of both forms of RBF may include meningitis, endocarditis, myocarditis, hepatitis, nephritis, and splenomegaly.
Codes
ICD10CM:A25.0 – Spirillosis
SNOMEDCT:
19044004 – Spirillary fever
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Differential Diagnosis & Pitfalls
- RBF due to S moniliformis – 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).
- 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 forms (especially Mycobacterium marinum) can present with nodular lymphangitis.
- Cutaneous leishmaniasis (Old World, New World) – Cutaneous lesion (papule, nodule, or ulcer) can be associated with lymphangitis or lymphadenopathy.
- Sexually transmitted diseases including syphilis, lymphogranuloma venereum, and chancroid
- Streptococcal or staphylococcal lymphadenitis
- Herpes simplex infection (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 form 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:06/16/2021
Last Updated:06/16/2021