Treatment of Rat Bite Fever
Penicillin G (12-20 million units/day for 3-4 weeks) is the first-line treatment for rat bite fever, with amoxicillin-clavulanate or doxycycline as effective alternatives for less severe cases. 1
Causative Organisms and Clinical Presentation
Rat bite fever is a rare but potentially fatal zoonotic disease caused by:
- Streptobacillus moniliformis (most common in North America and Europe)
- Spirillum minus (more common in Asia)
The clinical presentation typically includes:
- Fever (though not always present) 2
- Maculopapular rash (often on extremities, palms, and soles)
- Migratory polyarthralgia or arthritis (occurs in up to 50% of cases)
- Symptoms usually appear 3-10 days after exposure
- Potential for severe complications including endocarditis, meningitis, sepsis, and multi-organ failure 3
Diagnostic Approach
Diagnosis can be challenging due to:
- Non-specific symptoms that mimic other infectious diseases
- Absence of fever or rash in some cases 2
- Difficulty in isolating the organism in standard culture media
Blood cultures using specialized media are the gold standard for diagnosis, with 16S rRNA sequencing helpful for definitive identification 4.
Treatment Protocol
First-line Treatment:
- Intravenous Penicillin G: 12-20 million units/day divided every 4-6 hours for 3-4 weeks 1
- This dosage is specifically indicated for rat bite fever in the FDA labeling
Alternative Regimens:
- For less severe cases or outpatient treatment:
For Severe Infections:
- Ampicillin-sulbactam for hospitalized patients 7, 4
- Consider adding gentamicin for patients with endocarditis or meningitis
Duration of Therapy:
Wound Management
For patients presenting with a visible rat bite:
- Immediate wound cleansing with water or dilute povidone-iodine solution 5
- Avoid primary closure of the wound except for facial wounds 5
- Consider tetanus prophylaxis if vaccination status is outdated or unknown 5
Monitoring and Follow-up
- Assess for clinical response within 24-48 hours of initiating therapy 5
- Monitor for complications including endocarditis, meningitis, and sepsis
- For patients with arthritis, follow joint symptoms until complete resolution
Special Considerations
High-Risk Patients:
- Immunocompromised individuals
- Patients with liver disease (particularly cirrhosis) 4
- Elderly patients
- These patients may require longer treatment courses and closer monitoring
Prevention:
- Proper handling of rats and rodents
- Prompt cleansing of any bites or scratches
- Avoiding contact with wild rats
- Proper housing and veterinary care for pet rats
Clinical Pearls
- Rat bite fever can occur even without a visible bite wound or history of rat exposure
- The mortality rate is approximately 10% in untreated cases 3
- Treatment should begin promptly when rat bite fever is suspected, even before confirmatory diagnosis
- The classic triad of fever, rash, and arthralgia should raise suspicion for rat bite fever in anyone with rodent exposure