PNEUMONIA caused by a parasitic protozoan, Pneumocystis carinii which produces an opportunistic infection in the lung dangerous for people whose immune system is impaired (see IMMUNITY). In the past it was a major cause of death in people with AIDS/HIV. Fever, dry cough and breathlessness are among the symptoms; treatment is with high doses of antibiotic drugs such as CO-TRIMOXAZOLE or PENTAMIDINE.