ABSTRACT
Molecular biological applications such as polymerase chain reaction (PCR), DNA sequencing, and various fragment analysis methods have had a tremendous impact on our understanding of the biology of the different Pneumocystis species and the epidemiology of Pneumocystis pneumonia in humans. For example, in the definitive textbook on clinical parasitology used in the 1970s, prior to the molecular revolution, PcP was thought to be caused by the protozoan Pneumocystis carinii. The reservoir was considered to be various nonhuman hosts, including rodents such as rats and mice, which were ‘‘presumed to be carriers of the organism’’ [1]. Infections in humans were known chiefly from a relatively small number of cases, primarily in premature and malnourished infants. With the advent of the AIDS epidemic in the early 1980s, the disease emerged as an important public health problem. Infections in HIV-positive individuals occurred in over 60% of all patients and were associated with a case fatality rate of close to 25% [2-4]. Disease was thought to be the result of activated latent infections, which were acquired very early in life.
