Spirillum minus

Spirillum minus (Asian rat-bite fever)

• Also known as sodoku (rat-poison) in Japan

Microbiology

• Short, thick, Gram-negative rod in a tight coil
• Two to six helical turns, with terminal polytrichous flagella

Epidemiology

• From exposure, usually bite or scratch, of a rat or other rodent
  • S. minus is found in 25% of rats in Asia

Pathophysiology

• Relapses may relate to reactivation at the site of the original bite

Clinical Presentation

• Incubaction period of 1 to 4 weeks
• Initial bite heals but then becomes painful, swollen, and purple
  • Local lymphangitis and lymphadenitis
• Fevers, chills, headache, and malaise
  • Arthralgias/myalgias are rare
• Bite site becomes chancroid and indurated, with an eschar
• A rash develops, which is blotchy, reddish-brown, and macular, on the extremities, face, scalp, and trunk
  • Fades during afebrile periods
  • May be urticarial
• Leukocytosis, and 50% have false-positive nontreponemal syphilis test
• Fever is relapsing-remitting (on for 3 to 4 days, with a 3 to 9 day interval)
• May spontaneously resolve in 1 to 2 months, but can last years
• Can cause endocarditis; also, myocarditis, pleural effusions, hepatitis, splenomegaly, meningitis, epididymitis, conjunctivitis, and anemia
• Mortality 5-10% without antibiotics

Diagnosis

• Can be sen on blood and lymph node tissue with Giemsa stain, Wright stain, or darkfield microscopy
• Can also be intraperitoneally innoculated into mice or guinea pigs, and recovered at 1 to 3 weeks
• No current serology or PCR

Management

• Same as [Streptococcus moniliformis](Streptobacillus moniliformis (rat-bite fever).md)