Rat-bite fever agents
- Bacterium
Gram-negative
Thin wall with an outer membrane: stains pink.- For completeness
Bacteria carried by healthy rats that cause fever, rash on the hands and feet and painful joints after a bite, a scratch or contaminated food.
Also called: Streptobacillus moniliformis, Spirillum minus, Haverhill fever, sodoku
Quick facts
- Type
- Bacterium · Other clinically important bacteria
- Gram / shape
- Gram-negative · S
- Spread
- Bite or scratch of a rat or other rodent
- Causes
- Rat-bite fever · Septic or reactive arthritis · Sodoku
- Treatment
- Penicillin is the drug of choice
At a glance
- Gram
- Gram-negative
- Shape
- S. moniliformis: pleomorphic rods with bead-like swellings; Spirillum minus: short, tightly coiled spiral
- Oxygen
- S. moniliformis: facultative anaerobe, fastidious
- Family
- Leptotrichiaceae (Streptobacillus); Spirillaceae (Spirillum)
- Stain
- S. minus is seen with Giemsa, Wright or dark-field microscopy; it cannot be cultured
Morphology
- S. moniliformis: Gram-negative rods that form chains and filaments like a string of beads
- Needs media enriched with blood or serum; inhibited by the anticoagulant in many blood-culture bottles (sodium polyanethol sulfonate)
- Can form wall-deficient (L-form) variants
Transmission
- Bite or scratch of a rat or other rodent
- Contact with rodent saliva or urine, including handling or kissing pet rats
- Ingestion of contaminated milk, water or food (Haverhill fever)
- Not spread from person to person
Reservoir: Healthy rats, mice and other rodents; animals that catch rodents can carry it
Isolation precautions
What the care team adds to standard precautions.
- Standard
Virulence factors
- Spreads through the blood to skin, joints and heart valves
- L-forms may help it persist despite treatment
Diseases it causes
- Rat-bite fever: fever, rash and migratory polyarthralgia (S. moniliformis)
- Septic or reactive arthritis Septic Arthritis of the Knee →
- Endocarditis, the most serious complication Infective endocarditis →
- Sodoku (S. minus, mainly Asia): relapsing fever with ulceration at the bite and swollen lymph nodes
Clinical picture
- Abrupt fever, chills, vomiting, headache and muscle pain usually 3–10 days after contact
- Rash on the hands and feet, sometimes with petechiae or pustules
- The bite usually heals fast in S. moniliformis infection; in sodoku it ulcerates again
Diagnosis
- Ask about rodent contact and tell the laboratory
- Blood or joint fluid culture on enriched media without the inhibitory anticoagulant
- PCR or 16S rRNA sequencing; MALDI-TOF mass spectrometry on isolates
- S. minus: direct microscopy of blood or lesion material
Treatment
Penicillin is the drug of choice; doxycycline or streptomycin are options for penicillin allergy, and endocarditis is treated with penicillin plus an aminoglycoside. Early treatment prevents most deaths.
Drug class only; doses and regimens are set by the clinician from the current guideline.
In Pharmacology:
Prevention
- Avoid contact with rodents; rodent control at home and work
- Gloves and hand washing when handling pet or laboratory rodents
- Clean bites promptly and seek care
- Pasteurised milk and safe water
Test yourself
Think of the answer, then tap the question to see it.
Which bacterium causes rat-bite fever in the Americas?
Streptobacillus moniliformis.
What is Haverhill fever?
Rat-bite fever acquired by eating or drinking food, milk or water contaminated by rats.
Why may S. moniliformis fail to grow in routine blood-culture bottles?
The anticoagulant sodium polyanethol sulfonate inhibits it, and it needs enriched media.
Which antibiotic is the drug of choice for rat-bite fever?
Penicillin.
Connections
← Back to the group: Other clinically important bacteria
Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: About Rat Bite Fever (RBF) | Rat-bite Fever (RBF) | CDC (CDC, 2024); Rat Bite Fever and Streptobacillus moniliformis (Clinical Microbiology Reviews (ASM), 2007).
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Representative model, for educational purposes only.