Clinical Scenario:
A 6-year-old boy is brought to the emergency department with high-grade intermittent fever for 4 days. Ten days earlier, he was bitten on the hand by a rat while playing near a garbage area. The bite wound healed without treatment.
Over the last 2 days, he has developed painful swelling of both knees and ankles, followed by a faint maculopapular rash over his extremities. On examination, he is febrile and uncomfortable. There is no meningism, and the original bite wound appears completely healed.
Which of the following is the most likely diagnosis?
A. Cat-scratch disease
B. Hantavirus infection
C. Rat-bite fever
D. Streptococcal toxic shock syndrome
E. Tularemia
Correct answer & Explanation:
Correct answer: C. Rat-bite fever
Explanation
Rat-bite fever is a systemic bacterial infection that typically develops several days after exposure to a rat, even when the original bite wound has completely healed.
The classic presentation includes:
- Acute or intermittent fever
- Maculopapular or petechial rash, often involving the extremities
- Migratory arthralgia or frank arthritis, particularly involving large joints
- Headache, vomiting and myalgia may also occur.
The most common cause is Streptobacillus moniliformis. Another important cause, particularly in parts of Asia, is Spirillum minus, which produces a more localized/recurrent febrile illness known as sodoku.
In this child, the combination of rat bite 10 days earlier, subsequent fever, rash and painful swollen joints strongly supports rat-bite fever. The absence of an active wound does not exclude the diagnosis.
Why the other options are less likely:
- Cat-scratch disease: associated with cats and typically causes regional lymphadenopathy.
- Hantavirus infection: acquired mainly through exposure to infected rodent excreta; pulmonary or renal syndromes are characteristic rather than arthritis with rash.
- Streptococcal toxic shock syndrome: causes severe systemic toxicity, hypotension and multiorgan involvement.
- Tularemia: can follow animal exposure but classically produces an ulceroglandular syndrome with regional lymphadenopathy rather than this characteristic fever–rash–arthritis pattern.
