PNEUMOCYSTIS CARINII—ETIOLOGIC AGENT OF INTERSTITIAL PLASMA CELL PNEUMONIA OF PREMATURE AND YOUNG INFANTS

Abstract

Pneumocystis carinii, a parasite found almost a half century ago in the lungs of small mammals and of man in Brazil and, subsequently, in the lungs of man and of wild and laboratory rodents in Europe, has been identified with increasing frequency in the lungs of patients dying from interstitial plasma cell pneumonia of premature and young infants. The microorganism is found with considerable regularity in such patients, and has, in addition, been found in material obtained by lung puncture during life. Although its morphologic characteristics and life cycle have been well worked out, its taxonomic position remains a matter of conjecture. It has been tentatively classed as a protozoan of the Class Haplosporidia, but many authors believe it to be a fungus. The organism is not often encountered in the lungs in serial, unselected necropsies, but it has been found occasionally in lungs of older children and adults debilitated by chronic infections or malignant neoplasm and rather more frequently in association with cytomegalic inclusions in the lungs and salivary glands of infants and adults. However, it has been regularly identified in lungs of interstitial plasma cell pneumonia patients with only rare exceptions. Recently infection with what appears to be this microorganism has been transmitted to infant mice and kittens. The wide geographic distribution of natural infection with this agent in wild and domestic mammals of many species, the fact that it was first discovered in man and animals in South America, its frequent identification in the lungs of infants afflicted with this unique pneumonia of infancy, a disease which has now been reported in the United States, and the recent identification of Pneumocystis carinii in a diseased human lung from Canada, make it essential that American pediatricians be aware of this parasite as a potential human pathogen. Only further study will establish clearly what role this organism plays in the pathogenesis of human disease and settle the controversy as to whether it is fungal or protozoan.