Pneumocystis jirovecii pneumonia historical perspective

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]


Historical Perspective

The earliest report of this genus appears to have been that of Carlos Chagas in 1909[1] who discovered it in experimental animals but confused it with part of the life-cycle of Trypanosoma cruzi (causal agent of Chagas Disease) and later called both organisms 'Schizotrypanum cruzi' a form of trypanosome infecting humans.[2] The rediscovery of Pneumocystis cysts was reported by Antonio Carini in 1910 also in Brazil.[3] The genus was again discovered in 1912 by Delanoë and Delanoë this time at the Pasteur Institute in Paris, France who found it in rats and who proposed the genus and species name Pneumocystis carinii after Carini.[4]

Pneumocystis was redescribed as a human pathogen in 1942 by two Dutch investigators, van der Meer and Brug who found it in three new cases: a 3-month-old infant with congenital heart disease and in 2 of 104 autopsy cases - a 4-month-old infant and a 21-year-old adult.[5] There being only one described species in the genus, they considered the human parasite to be P. carinii. Nine years later (1951) Dr. Josef Vanek at Charles University in Prague in Prague, Czechoslovakia showed in a study of lung sections from sixteen children that the organism labelled "P. carinii" was the causative agent of pneumonia in these children.[6] The following year (1952) Jírovec reported "P. carinii" as the cause of interstitial pneumonia in neonates.[7][8][9] Following the realization that Pneumocystis from humans could not infect experimental animals such as rats, and that the rat form of Pneumocystis differed physiologically and had different antigenic properties, Frenkel[10] was the first to recognize the human pathogen as a distinct species. He named it Pneumocystis jirovecii (see nomenclature above). There has been controversy over the relabeling of P. carinii in humans as P. jirovecii,[11] which is why both names still appear in publications. However, only the name P. jirovecii is used exclusively for the human pathogen, whereas the name P. carinii has had a broader application to many species.[12] Frenkel and those before him, believed that all Pneumocystis were protozoans, but soon afterwards evidence began accumulating that Pneumocystis was a fungal genus. Recent studies show it to be an unusual, in some ways a primitive genus of Ascomycota, related to a group of yeasts.[13] Every tested primate, including humans, appears to have their own type of Pneumocystis that is incapable of cross-infecting other host species and has co-evolved with each mammal species.[14] Currently only 5 species have been formally named: P. jirovecii from humans, P. carinii as originally named from rats, P. murina from mice,[15] P. wakefieldiae[16][17] also from rats, and P. oryctolagi from rabbits.[18]

Historical and even recent reports of P. carinii from humans are based upon older classifications (still used by many, or those still debating the recognition of distinct species in the genus Pneumocystis) which does not mean that the true P. carinii from rats actually infects humans. In an intermediate classification system, the various taxa in different mammals have been called formae speciales or forms. For example the human "form" was called Pneumocystis carinii f. [or f. sp.] hominis, while the original rat infecting form was called Pneumocystis carinii f. [or f. sp.] carinii. This terminology is still used by some researchers. The species of Pneumocystis species originally seen by Chagas have not yet been named as distinct species. Many other undescribed species presumably exist and those that have been detected in many mammals are only known from molecular sample detection from lung tissue or fluids, rather than by direct physical observation.[19] As of yet, they are cryptic taxa.


  1. Chagas C (1909). "Neue Trypanosomen". Vorläufige Mitteilung. Arch. Schiff. Tropenhyg. 13: 120–122.
  2. Chagas C (1909). "Nova tripanozomiase humana: Estudos sobre a morfolojia e o ciclo evolutivo do Schizotrypanum cruzi n. gen., n. sp., ajente etiolojico de nova entidade morbida do homem". Mem Inst Oswaldo Cruz. 1 (2): 159–218.
  3. Carini A. (1910). "Formas des eschizogonia do Trypanosoma lewisi". Soc Med Cir São Paulo. 38 (8): &ndash, .
  4. Delanoë P, Delanoë M. (1912). "Sur les rapports des kystes de Carini du poumon des rats avec le Trypanosoma lewisi". Comptes rendus de l’Academie des sciences. 155: 658&ndash, 61.
  5. van der Meer MG, Brug SL. (1942). "Infection à Pneumocystis chez l'homme et chez les animaux". Amer Soc Belge Méd Trop. 22: 301&ndash, 9.
  6. Vanek J. (1951). "Atypicka (interstitiálni) pneumonie detí vyvolaná Pneumocystis carinii (Atypical interstitial pneumonia of infants produced by Pneumocystis carinii)". Casop lék cesk. 90: 1121&ndash, 4.
  7. Jírovec O. (1952). "Pneumocystis carinii puvodce t. zv intertitialnich plasmocelularnich pneumonii kojencw (Pneumocystis carinii, the cause of interstitial plasmacellular pneumonia in neonates)". P Csl. Hyg epid mikrob. 1: 141.
  8. Vanek J, Jírovec O, Lukes J. (1953). "Interstitial plasma cell pneumonia in infants". Ann Paediatrici. 180: 1&ndash, 21.
  9. Gajdusek DC (1957). "Pneumocystis carinii; etiologic agent of interstitial plasma cell pneumonia of premature and young infants". Pediatrics. 19: 543&ndash, 65.
  10. Frenkel JK (1976). "Pneumocystis jiroveci n. sp. from man: morphology, physiology, and immunology in relation to pathology". Natl Cancer Inst Monogr. 43: 13–27. PMID 828240.
  11. Gigliotti F (2005). "Pneumocystis carinii: has the name really been changed?". Clin Infect Dis. 41 (12): 1752–5. PMID 16288399.
  12. Hawksworth DL (2007). "Responsibility in naming pathogens: the case of Pneumocystis jirovecii, the causal agent of pneumocystis pneumonia". Lancet Infect. Dis. 7(1): 3–5. PMID 17182335.
  13. James TY; et al. (2006). "Reconstructing the early evolution of Fungi using a six-gene phylogeny". Nature. 443: 818–822.
  14. Hugot J, Demanche C, Barriel V, Dei-Cas E, Guillot J (2003). "Phylogenetic systematics and evolution of primate-derived Pneumocystis based on mitochondrial or nuclear DNA sequence comparison". Syst Biol. 52: 735–744.
  15. Keely S, Fischer J, Cushion M, Stringer J (2004). "Phylogenetic identification of Pneumocystis murina sp. nov., a new species in laboratory mice". Microbiology. 150 (Pt 5): 1153–65. PMID 15133075.
  16. Cushion MT, Keely SP, Stringer JR (2004). "Molecular and phenotypic description of Pneumocystis wakefieldiae sp. nov., a new species in rats". Mycologia. 96: 429–438.
  17. Cushion MT, Keely SP, Stringer JR (2005). "Validation of the name Pneumocystis wakefieldiae". Mycologia. 97: 268–268.
  18. Dei-Cas E; et al. (2006). "Pneumocystis oryctolagi sp. nov., an uncultured fungus causing pneumonia in rabbits at weaning: review of current knowledge, and description of a new taxon on genotypic, phylogenetic and phenotypic bases". FEMS Micriobiol. Rev. 30(6): 853–871. PMID 17064284.
  19. Demanche C; et al. (2001). "Phylogeny of ‘’Pneumocystis carinii’’ from 18 primate species confirms host specificity and suggests coevolution". J. Clinical Microbiol. 39 (6): 2126–2133. PMID 11376046.

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