Season 5, Episode 15

A priest presents with hallucinations, progressive numbness, toe necrosis, chest pain, and transient blindness. The team initially suspects multiple conditions including AIDS before diagnosing Wiskott-Aldrich Syndrome, a genetic immunodeficiency that explains all his symptoms by impairing his immune system and making him susceptible to opportunistic infections.

Also known as: PCP

Traces of pneumocystis, a normally harmless organism, are found in the priest's spleen. This opportunistic infection is significant because it initially leads the team to suspect AIDS, but ultimately helps them recognize the underlying immunodeficiency (Wiskott-Aldrich syndrome) that allowed the infection to occur.