Spirillum minus infection is a zoonotic bacteria caused by Spirillum minus, a Gram-negative rod (also known as Spirillum minor). It’s a kind of rat-bite fever (RBF). S. minus is more widespread in Asia than in the United States and other parts of North America, where Streptobacillus moniliformis causes most rat-bite fever cases. In Japan, the S. minus infection is known as Sodoku (so, “rat”; doku, “poison”).

S. minus is a spiral bacillus that is tightly coiled and gram-negative. Infection occurs as a result of rat bite inoculation. Up to one-fourth of rats had S. minus in their conjunctiva, blood, sputum, or nasopharynx. Unlike streptobacillary rat-bite fever, Spirillum minus infection does not occur after you consume the organism. Furthermore, infection transmission between people does not happen.


Spirillum minus infection symptoms may include:

  • Chills
  • Fever
  • Lymph nodes are swollen surrounding the bite
  • Open wound where the bite happened
  • Rash with pimples and red or purple spots

Symptoms caused by the bacterium often disappear within two weeks. If left untreated, symptoms such as fever or joint discomfort might reoccur for several weeks or longer.


Giemsa stain, Wright stain, and darkfield microscopy are three methods that may be utilized to directly see S. minus in blood and infected tissues, respectively. The recovery of organisms from mice or guinea pigs 1 to 3 weeks after intraperitoneal injection of infected material from the index patient may be used to confirm the diagnosis of S. minus infection.


Penicillin is the first-line therapy for Spirillum minus infection; generally, IV Benzylpenicillin 1.2g 4 hourly for at least 1 week, followed by oral Penicillin V for a total of 2 weeks. In penicillin-allergic individuals, IV Ceftriaxone 1g OD and IV Doxycycline 100mg BD are alternatives. Treatment for septic arthritis and endocarditis should be maintained for 4 weeks.

If Spirillum minus infection is not detected and treated promptly, it may lead to severe illness and death.

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