Pneumocystis pneumonia

Pneumocystis pneumonia (PCP) or pneumocystosis is a form of pneumonia, caused by the yeast-like fungus Pneumocystis jirovecii. This pathogen is specific to humans. It has not been shown to infect other animals, while other species of Pneumocystis that parasitize other animals (all of which are mammals) have not been shown to infect humans.

Pneumocystis is commonly found in the lungs of healthy people, but being a source of opportunistic infection it can cause a lung infection in people with a weakened immune system. Pneumocystis pneumonia is especially seen in people with cancer, HIV/AIDS and the use of medications that affect the immune system.

The causal agent is known as P. jiroveci or P. jirovecii. Also the older name Pneumocystis carinii is, although incorrect for the human variant, still in common usage. The nomenclature is described below.

As a result, Pneumocystis pneumonia (PCP) is also known as Pneumocystis jiroveci[i] pneumonia and as Pneumocystis carinii pneumonia.