Pneumocystic carinii pneumonia
Overview
Pneumocystis pneumonia (PCP) is a form of pneumonia caused by the yeast-like fungus, Pneumocystis jirovecii. This species of fungus 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.[1] The causal agent was originally described as a protozoan and spelled P. jiroveci and prior to then was classified as a form of Pneumocystis carinii, a name still in common usage.[2][3] These names are discussed below. As a result, Pneumocystis pneumonia (PCP) has also been known as Pneumocystis jiroveci[i] pneumonia and as Pneumocystis carinii pneumonia, as is also explained below.[4][5][6] Confusion caused by the misapplication of the name P. carinii to all species of Pneumocystis may incorrectly suggest that the human pathogen could reside in other animals, including domesticated animals
Symptoms
Symptoms of PCP include fever, non-productive cough, shortness of breath (especially on exertion), weight loss and night sweats. There is usually not a large amount of sputum with PCP unless the patient has an additional bacterial infection. The fungus can invade other visceral organs, such as the liver, spleen and kidney, but only in a minority of cases
Diagnosis
The diagnosis can be confirmed by the characteristic appearance of the chest x-ray which shows widespread pulmonary infiltrates, and an arterial oxygen level (pO2) strikingly lower than would be expected from symptoms. The diagnosis can be definitively confirmed by pathologic identification of the causative organism in induced sputum or bronchial washings obtained by bronchoscopy with coloration by toluidine blue or immunofluorescence assay, which will show characteristic cysts
Treatment
The name P. jirovecii, to distinguish the organism found in humans from physiological variants of Pneumocystis found in other animals, was first proposed in 1976, in honor of Otto Jirovec, who described Pneumocystis pneumonia in humans in 1952. After DNA analysis showed significant differences in the human variant, the proposal was made again in 1999 and has come into common use; P. carinii still describes the species found in rats[2] and that name is typified by an isolate from rats.[3] The International Code of Botanical Nomenclature (ICBN) requires that the name to be spelled jirovecii rather than jiroveci. The latter spelling originated when Pneumocystis was believed to be a protozoan, rather than a fungus, and therefore was spelled using the International Code of Zoological Nomenclature; both spellings are commonly used. A change in the ICBN in 2005 now recognizes the validity of the 1976 publication, making the 1999 proposal redundant, and cites Pneumocystis and P. jirovecii as examples of the change in ICBN Article 45, Ex 8. The name P. jirovecii is typified (both lectotypified and epitypified) by samples from human autopsies dating from the 1960s.