Pneumocystis jirovecii

Pneumocystis jirovecii is an ascomycete, specific for humans, characterized by a strong tropism for the lungs and airborne host-to-host transmission. This pathogen constitutes a unique phenomenon in medical mycology. Pneumocystis pneumonia (PCP) was a major cause of morbidity and mortality among patients with HIV during the 1980s and 1990s, and it remains the main cause of AIDS-defining disease in developed countries. However, an increased frequency of PCP in patients without AIDS but with defects in cellular or global immunity has been reported. The fungus is also a comorbidity factor in acute or chronic pulmonary diseases. Thus, Pneumocystis infections remain a serious public health issue, as attested by the 250 publications published annually on this topic recorded by the National Center for Biotechnology Information. Here, we summarize the present knowledge of P. jirovecii fundamental biology and epidemiology. View Large Image Figure Viewer Download Hi-res image (A) Ascus containing ascospores (indicated by the arrow, Wright Giemsa stain, × 1000). (B) Asci (Toluidine blue stain, × 400). (C) Cluster of Pneumocystis jirovecii organisms (indicated by the arrow, Wright Giemsa stain, × 100). (D) Asci [two-step indirect fluorescent antibody (IFA), anti-ascus antibodies, MONOFLUO Kit P. jirovecii Bio-Rad, × 400].