Infected infants show extensive plasma cell infiltration of the alveolar septae, but immunosuppressed children and adults do not. Epidemiology Pneumocystis carinii has been found in the lungs of rats, rabbits, mice, dogs, sheep, goats, ferrets, chimpanzees, guinea pigs, horses, and monkeys. The organism has been reported in lower animals and humans from all continents. Because about 70 percent of healthy individuals may have humoral antibody to P carinii , subclinical infection must be highly prevalent. Diagnosis Tachypnea and fever are consistent features of the pneumonitis, and diffuse bilateral alveolar disease can be observed by radiography.
Diagnosis requires the identification of P carinii in pulmonary tissue or lower airway fluids.
Such specimens may be obtained by lung biopsy, inducement of sputum, bronchoalveolar lavage, or needle aspiration of the lung. Serologic studies for antibodies and antigen are not helpful in establishing a specific diagnosis. Four drugs currently available for therapy of P carinii pneumonitis are pentamidine isethionate, trimethoprim-sulfamethoxazole, atovaquone and trimetrevate. Trimethoprim-sulfamethoxazole is preferred because of its low toxicity and greater efficacy. Ribosomal RNA sequence shows Pneumocystis carinii to be a member of the fungi.