Genetics, metabolism and host specificity of Pneumocystis carinii.

Pneumocystis carinii is a major cause of severe pneumonia in immunosuppressed individuals, especially in those with human immunodeficiency virus (HIV) infection during their period of progression to acquired immunodeficiency syndrome (AIDS), and constitutes a worldwide problem to public health. Recently, significant advances in the development of experimental animal models of P. carinii infection, as well as in our knowledge of the genetic diversity and taxonomy of P. carinii, have been made. These advances may contribute to our understanding of the transmission of P. carinii pneumonia (PCP) and to the development of new prevention and control strategies. This paper addresses questions relating to the epidemiology of PCP including the detection of the parasite in the environment and in patients, the mechanism of genetic variation of the major surface glycoprotein (MSG) of P. carinii, and host-related genetic variation among isolates of this organism, emphasizing phenotypic expression and its impact on epidemiology and taxonomy.