**Core Concept**
Leptospirosis is a zoonotic disease caused by the bacterium *Leptospira*, primarily acquired through contact with water or soil contaminated with the urine of infected animals. Early diagnosis is crucial in preventing severe complications.

**Why the Correct Answer is Right**
Antibodies against *Leptospira* are typically detectable after the first week of infection, as the immune system takes time to mount an effective response. This delay in antibody production can make early diagnosis challenging. In the first week, patients are more likely to be diagnosed based on clinical presentation and laboratory findings such as elevated liver enzymes and kidney function tests.

**Why Each Wrong Option is Incorrect**
**Option A:** Infection can indeed be acquired through direct contact with infected urine, as the bacteria can penetrate the skin or mucous membranes. This is a common mode of transmission in occupational settings, such as farming or handling infected animals.
**Option B:** Mortality rates in severe cases of leptospirosis can range from 5-15%, which is a significant concern. Prompt treatment is essential to prevent death.
**Option D:** IV penicillin is recommended for the treatment of severe cases of leptospirosis, as it is effective against *Leptospira*. Early antibiotic therapy can significantly improve outcomes.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that leptospirosis can masquerade as other diseases, such as dengue fever or malaria, making early diagnosis and treatment critical. A high index of suspicion is necessary, especially in patients with a history of exposure to contaminated water or soil.

**✓ Correct Answer:** C. Antibodies are usually detectable in the first week