Pneumocystis jiroveci

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Photomicrograph of lung tissue showing an alveolar cast.
Photomicrograph of lung tissue with Grocott staining. Pneumocystis jiroveci organisms are highlighted as black, disc-like entities within the alveolar cast.

Unicellular fungal organism previously known as Pneumocystic carinii and also previously thought to be a protozoon. Causative agent in pneumocystis pneumonia.

Exposure to organism is almost universal and immunity is acquired at a young age.[1][2] The organism is normally kept at bay and clinical disease was previously seen only in frail individuals, e.g. malnourished children and in association with immunosuppression.

A large number of cases were seen in the 1980s with the advent of HIV/AIDS. It remains one of the most common opportunistic infections in AIDS (less so in Africa, at least West Africa[3]) and was one of the original 1987 AIDS-defining illnesses. Co-trimoxazole is given as prophylaxis in HIV patients.[4]


It was previously thought to be a trypanosome, then a protozoon before being classified as a fungal organism, albeit an unusual one. The stages of the 'life cycle' were named when it was classified as a protozoa and have been kept despite reclassification. The precise life cycle is not clearly understood as it has not been possible to culture the organism in vitro.

The organism was formerly called Pneumocystis carinii as it was morphologically indistinguishable from other Pneumocystis species that colonised other mammals. Genetic studies showed that the organism colonising humans was distinct[5] and it was suggested that it was renamed as Pneumocystic jiroveci in honour of Jírovec[6] who noticed in 1952 that the human form could not cross-infect rats and vice versa. The newer name (actually first used in 1976[7]) has been increasingly adopted, but not universally so, with detractors contending that sub-division by host species can be accommodated with as a suffix, e.g. Pneumocystis carinii humanus.[8]


  1. Pifer LL, Hughes WT, Stagno S, Woods D. Pneumocystis carinii infection: evidence for high prevalence in normal and immunosuppressed children. Pediatrics. 1978 Jan; 61(1):35-41.
  2. Vargas SL, Hughes WT, Santolaya ME, Ulloa AV, Ponce CA, Cabrera CE, Cumsille F, Gigliotti F. Search for primary infection by Pneumocystis carinii in a cohort of normal, healthy infants. Clinical infectious diseases : an official publication of the Infectious Diseases Society of America. 2001 Mar 15; 32(6):855-61.(Link to article – subscription may be required.)
  3. Lucas SB, Hounnou A, Peacock C, Beaumel A, Djomand G, N'Gbichi JM, Yeboue K, Hondé M, Diomande M, Giordano C. The mortality and pathology of HIV infection in a west African city. AIDS (London, England). 1993 Dec; 7(12):1569-79.
  4. [Guidelines on co-trimoxazole prophylaxis for HIV-related infections among children, adolescents and adults, WHO.] (Link to pdf version
  5. Demanche C, Berthelemy M, Petit T, Polack B, Wakefield AE, Dei-Cas E, Guillot J. Phylogeny of Pneumocystis carinii from 18 primate species confirms host specificity and suggests coevolution. Journal of clinical microbiology. 2001 Jun; 39(6):2126-33.(Link to article – subscription may be required.)
  6. Stringer JR, Beard CB, Miller RF, Wakefield AE. A new name (Pneumocystis jiroveci) for Pneumocystis from humans. Emerging infectious diseases. 2002 Sep; 8(9):891-6.
  7. Frenkel JK. Pneumocystis jiroveci n. sp. from man: morphology, physiology, and immunology in relation to pathology. National Cancer Institute monograph. 1976 Oct; 43:13-30.
  8. Gigliotti F. Pneumocystis carinii: has the name really been changed? Clinical infectious diseases : an official publication of the Infectious Diseases Society of America. 2005 Dec 15; 41(12):1752-5.(Link to article – subscription may be required.)
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