A 28-year-old HIV-positive male complains of pain on swallowing. Physical examination is remarkable for white plaque-like material on his tongue and buccal mucosa, which is scraped and sent to the laboratory. Based on these findings, and on the laboratory results, the man is diagnosed with acquired immunodeficiency syndrome (AIDS). With which of the following agents is the man most likely infected?

Candida albicans produces oral thrush, an AIDS-defining lesion, which is common in acute HIV disease, and becomes increasing common as the CD4 + cell count falls. The lesions are usually painless. Diagnosis is by demonstration of pseudohyphae using a wet smear with confirmation by culture. Although cytomegalovirus is associated with numerous clinical scenarios in the AIDS population, including odynophagia (painful swallowing), it would not produce white plaques on the oral mucosa. Herpes Simplex Iproduces vesicular lesions occurring in clusters in the oral cavity. There is an increased risk of herpes infections in the AIDS group, but the lesions do not resemble those described in the question. Human herpesvirus 8 is the causative agent of Kaposi's sarcoma, a malignancy arising from endothelial cells that appears as hemorrhagic nodules in different organ systems. It is the most common cancer in the HIV infected population.