A25 Rat-bite fevers

Name of the Condition

• Rat-bite fevers

Summary

Rat-bite fevers are bacterial infections transmitted through bites or scratches from infected rodents, such as rats, or contact with their urine or secretions. The condition is characterized by fever, rash, and systemic symptoms, with two main causative agents: Streptobacillus moniliformis (most common in the United States) and Spirillum minus (more prevalent in Asia). Onset typically occurs 3–10 days after exposure, though symptoms may appear earlier or later depending on the pathogen.

Causes

Rat-bite fevers are caused by Streptobacillus moniliformis or Spirillum minus, bacteria carried by rodents. Infection occurs when these bacteria enter the body through a bite, scratch, or contact with contaminated rodent urine, droppings, or nesting materials. The bacteria can also spread through consumption of food or water contaminated with rodent excreta.

Risk Factors

• Close contact with rodents (e.g., pet rats, wild rats, or mice)
• Occupational exposure (e.g., laboratory workers, pest control, or farmers)
• Living in or traveling to areas with high rodent infestation
• Handling rodents without protective measures (e.g., gloves)
• Poor sanitation or storage of food that attracts rodents

Symptoms

• Sudden onset of fever (often high)
• Chills and headache
• Muscle or joint pain
• Rash (may be maculopapular, petechial, or purpuric)
• Ulceration at the bite or scratch site (for Spirillum minus)
• Arthritis or joint swelling (especially with Streptobacillus moniliformis)
• Vomiting, nausea, or abdominal pain

Diagnosis

Diagnosis is based on clinical history (exposure to rodents) and symptoms. Laboratory confirmation may involve blood or tissue cultures to identify the causative bacteria. Serologic tests or PCR may be used in some cases, though culture remains the gold standard. Imaging or other tests may be performed to rule out complications.

Treatment Options

• Antibiotics: Penicillin, doxycycline, or erythromycin are first-line treatments. Duration depends on severity and response.
• Supportive care: Rest, hydration, and pain management for systemic symptoms.
• Wound care: Cleaning and disinfecting bite or scratch sites to prevent secondary infection.

Prognosis and Follow-Up

With prompt antibiotic treatment, most patients recover fully within 1–2 weeks. Delayed treatment may lead to prolonged illness or complications. Follow-up is recommended to monitor for recurrence or late-onset symptoms, especially if the initial infection was severe.

Complications

• Septic arthritis (joint infection)
• Endocarditis (heart valve infection)
• Meningitis (rare)
• Pneumonia or respiratory involvement
• Systemic sepsis (if untreated)

Lifestyle & Prevention

• Avoid contact with wild or pet rodents; use protective gear (gloves) when handling them.
• Keep living spaces clean and free of rodent infestations (seal entry points, store food in sealed containers).
• Practice good hand hygiene after handling rodents or their environments.
• Seek prompt medical care for rodent bites or scratches, even if minor.

When to Seek Professional Help

• Fever or rash develops after rodent exposure or a bite/scratch.
• Symptoms worsen or persist beyond a few days.
• Signs of systemic infection (e.g., severe headache, joint pain, or difficulty breathing).
• Wound shows signs of infection (redness, swelling, pus).

Tips for Medical Coders

• Use code A25 for rat-bite fevers, specifying the causative agent if documented (Streptobacillus moniliformis or Spirillum minus).
• Document exposure history (e.g., bite, scratch, or contact with rodent secretions) to support the diagnosis.
• Include any associated complications (e.g., septic arthritis) with additional codes as needed.
• Ensure the code aligns with clinical documentation to reflect the specific presentation and treatment.