An HIV-positive patient presents with a purple-colored lesion on the tongue. Which organism is responsible for this lesion?

Correct answer: B. Human herpesvirus 8 (HHV-8)

• A. HBV is a hepatotropic virus and does not cause oral mucosal lesions.
• B. CORRECT. A purple lesion on the tongue of an HIV patient is classic for Kaposi's sarcoma (KS). KS is caused by HHV-8 (also called Kaposi's sarcoma-associated herpesvirus, KSHV). Oral KS typically appears as purple/brown flat or nodular lesions on the palate or tongue, and is an AIDS-defining illness.
• C. EBV causes oral hairy leukoplakia (white corrugated lesions on the lateral tongue) in HIV patients — not purple lesions.
• D. HSV causes recurrent herpetic ulcers in HIV patients. Lesions are painful ulcerations, not purple macules or nodules.