## Leptospirosis vs Rat-Bite Fever: Clinical Discrimination ### Context Both leptospirosis and rat-bite fever (Streptobacillus moniliformis) are zoonotic infections transmitted by rodents. They share fever, myalgia, and rash, making differentiation clinically important. ### Comparison Table | Feature | Leptospirosis | Rat-Bite Fever (Streptobacillus) | | --- | --- | --- | | **Conjunctival involvement** | **Suffusion (NO exudate)** | Conjunctivitis with exudate (rare) | | **Rash characteristics** | Maculopapular, trunk/limbs | Petechial/pustular, palms/soles | | **Biphasic fever** | Typical | Monophasic or relapsing | | **Arthralgia** | Later (immune phase) | Early and prominent | | **Incubation period** | 5–14 days | 3–10 days | | **Organism in blood** | Leptospiremia (first week) | Bacteremia throughout | | **Eschar at bite site** | Absent | May be present | ### Key Point: **Conjunctival suffusion WITHOUT exudate is pathognomonic for leptospirosis.** This is the single most specific clinical sign that distinguishes leptospirosis from other febrile illnesses, including rat-bite fever. ### High-Yield: **Conjunctival suffusion** = hallmark of leptospirosis. It is: - Non-purulent (no exudate) - Bilateral - Appears early (days 3–4) - Painless - NOT associated with photophobia (unlike bacterial conjunctivitis) ### Clinical Pearl: In a febrile patient from an endemic area with conjunctival suffusion, leptospirosis should be the leading diagnosis. The absence of exudate is the key differentiator from other causes of conjunctivitis. ### Mnemonic: **LEPT = Leptospirosis, Eye (Suffusion), Painless, Tropical**
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