Pneumocystis — A Genus Long Known, But with Relationships Only Recently Appreciated

Abstract

Chagas first described Pneumocystis in print in 1909, when he mistakenly identified it as a morphological form of Trypanosoma cruzi. Within a few years of this first report, further studies established that the microbe in question was not a Trypanosome, but a new species of microbe (Delanoe and Delanoe 1912). Hence, Pneumocystis can be regarded as an old organism since almost 100 years have passed since its existence and potential to cause disease were recognized. Description of the disease Pneumocystis causes proceeded relatively quickly, and significant advances were in place by 1970 (reviewed in Burke and Good 1973; Walzer et al. 1973). However, the fundamental nature of this microbe was slower to be defined and appreciated. Most investigators considered it to be a protozoon until 1998, when studies on its DNA began to provide the first unequivocal evidence that Pneumocystis is a fungus.