The given question describes a 12-year-old boy with a set of symptoms suggesting a probable infection. The symptoms include right upper quadrant pain, calf pain, conjunctival suffusion, icterus, fever, and tender hepatomegaly. Let's analyze the provided options to identify the most likely diagnosis:
- Chikungunya: This viral illness often presents with high fever, severe joint pain, and a rash. Hepatomegaly and jaundice are not typical features.
- Leptospirosis: This bacterial infection can cause symptoms such as fever, muscle pain (notably in the calves), conjunctival suffusion (reddening of the eyes without pus), jaundice, and liver enlargement. The symptoms match the description provided in the question.
- Dengue hemorrhagic fever: Known for high fever, bleeding manifestations, and plasma leakage, it does not typically present with conjunctival suffusion or significant calf pain.
- Encephalopathy caused by hepatitis A: While hepatitis A can cause jaundice and liver enlargement, encephalopathy (confusion, altered mental status) is a specific neurological symptom not indicated in the question.
Given the combination of symptoms described in the question, Leptospirosis is the most likely diagnosis. This condition aligns with the symptoms of fever, calf pain, and conjunctival suffusion. Therefore, the correct answer is Leptospirosis.