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Pneumocystis jirovecii

(Redirected fromPneumocystis carinii)

Pneumocystis jirovecii(previouslyP. carinii) is a yeast-likefungusof the genusPneumocystis.The causative organism ofPneumocystispneumonia,it is an importanthuman pathogen,particularly amongimmunocompromised hosts.Prior to its discovery as a human-specific pathogen,P. jiroveciiwas known asP. carinii.

Pneumocystis jirovecii
"P. jirovecii" cysts in tissue
P. jiroveciicysts in tissue
Scientific classificationEdit this classification
Domain: Eukaryota
Kingdom: Fungi
Division: Ascomycota
Class: Pneumocystidomycetes
Order: Pneumocystidales
Family: Pneumocystidaceae
Genus: Pneumocystis
Species:
P. jirovecii
Binomial name
Pneumocystis jirovecii
Synonyms
  • Pneumocystis carinii

Lifecycle

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The complete lifecycles of any of the species ofPneumocystisare not known, but presumably all resemble the others in the genus. The terminology follows zoological terms, rather than mycological terms, reflecting the initial misdetermination as aprotozoanparasite. It is an extracellular fungus. All stages are found in lungs and because they cannot be culturedex vivo,direct observation of livingPneumocystisis difficult. Thetrophozoitestage is thought to be equivalent to the so-called vegetative state of other species (such asSchizosaccharomyces pombe), which likePneumocystis,belong to theTaphrinomycotinabranch of the fungal kingdom.[1]The trophozoite stage is single-celled and appearsamoeboid(multilobed) and closely associated with host cells. Globular cysts eventually form that have a thicker wall. Within theseascus-like cysts, eight spores form, which are released through rupture of the cyst wall. The cysts often collapse, forming crescent-shaped bodies visible in stained tissue. Whethermeiosistakes place within the cysts, or what the genetic status is of the various cell types, is not known for certain.[2]

Homothallism

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The lifecycle ofP. jiroveciiis thought to include bothasexualandsexualphases.[3]Asexual multiplication ofhaploidcells likely occurs bybinary fission.The mode of sexual reproduction appears to be primaryhomothallism,a form ofself-fertilization.[3]The sexual phase takes place in the host's lungs. This phase is presumed to involve formation of a diploidzygote,followed bymeiosis,and then production of anascuscontaining the products of meiosis, eight haploidascospores.The ascospores may be disseminated by airborne transmission to new hosts.

Medical relevance

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Further information:Pneumocystis pneumonia

Pneumocystispneumonia is an important disease of immunocompromised humans, particularly patients withHIV,but also patients with an immune system that is severely suppressed for other reasons, for example, following abone marrow transplant.In humans with a normal immune system, it is an extremely commonsilent infection.[4]

Identified by methenamine silver stain of lung tissue,type I pneumocytes,andtype II pneumocytesover-replicate and damage alveolar epithelium, causing death by asphyxiation. Fluid leaks into alveoli, producing an exudate seen as honeycomb/cotton candy appearance onhematoxylin and eosin-stainedslides. Drug of choice istrimethoprim/sulfamethoxazole,pentamidine,ordapsone.In HIV patients, most cases occur when the CD4 count is below 200 cells per microliter.

Nomenclature

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At first, the namePneumocystis cariniiwas applied to the organisms found in both rats and humans, as the parasite was not yet known to behost-specific. In 1976, the name "Pneumocystis jiroveci"was proposed for the first time, to distinguish the organism found in humans from variants ofPneumocystisin other animals. The organism was named thus in honor of Czech parasitologistOtto Jirovec,who describedPneumocystispneumonia 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.[5]

The name was spelled according to theInternational Code of Zoological Nomenclature,since the organism was believed to be a protozoan. After it became clear that it was a fungus, the name was changed toPneumocystis jirovecii,[6]according to theInternational Code of Nomenclature for algae, fungi, and plants(ICNafp), which requires such names be spelled with double i (ii).[7] Both spellings are commonly used, but according to the ICNafp,P. jiroveciiis correct.[8]A change in the ICNafp now recognizes the validity of the 1976 publication, making the 1999 proposal redundant, and citesPneumocystisandP. jirovecias examples of the change in ICN Article 45, Ex 7. The nameP. jiroveciis typified (both lectotypified and epitypified) by samples from human autopsies dating from the 1960s. [9]

The term PCP, which was widely used by practitioners and patients, has been retained for convenience, with the rationale that it now stands for the more general Pneumocystis pneumonia rather than Pneumocystis carinii pneumonia.

The nameP. cariniiis incorrect for the human variant, but still describes the species found in rats, and that name is typified by an isolate from rats.[9]

Pneumocystisgenome

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Pneumocystisspecies cannot be grown in culture, so the availability of the human disease-causing agent,P. jirovecii,is limited. Hence, investigation of the whole genome of aPneumocystisis largely based upon trueP. cariniiavailable from experimental rats, which can be maintained with infections. Genetic material of other species, such asP. jirovecii,can be compared to the genome ofP. carinii.[10]

Microscopy image ofP. jirovecii

The genome ofP. jiroveciihas been sequenced from a bronchoalveolar lavage sample.[11]The genome is small, low inG+Ccontent, and lacks most amino-acid biosynthesis enzymes.

History

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The earliest report of this genus appears to have been that ofCarlos Chagasin 1909,[12]who discovered it in experimental animals, but confused it with part of the lifecycle ofTrypanosoma cruzi(causal agent ofChagas disease) and later called both organismsSchizotrypanum cruzi,a form oftrypanosomeinfecting humans.[13]The rediscovery ofPneumocystiscysts was reported byAntonio Cariniin 1910, also inBrazil.[14]The genus was again discovered in 1912 by Delanoë and Delanoë, this time at thePasteur Institutein Paris, who found it in rats and proposed the genus and species namePneumocystis cariniiafter Carini.[15]

Pneumocystiswas 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 withcongenital heart diseaseand in two of 104autopsycases – a 4-month-old infant and a 21-year-old adult.[16]There being only one describedspeciesin thegenus,they considered the human parasite to beP. carinii.Nine years later (1951), Dr. Josef Vanek atCharles University in Prague,Czechoslovakia, showed in a study of lung sections from 16 children that the organism labelled "P. carinii"was the causative agent of pneumonia in these children.[17]The following year, Czech scientistOtto Jírovecreported "P. carinii"as the cause ofinterstitial pneumoniainneonates.[18][19][20]Following the realization thatPneumocystisfrom humans could not infect experimental animals such as rats, and that the rat form ofPneumocystisdiffered physiologically and had differentantigenicproperties, Frenkel[21]was the first to recognize the human pathogen as a distinct species. He named it "Pneumocystis jiroveci"(corrected toP. jirovecii- see nomenclature above). Controversy existed over the relabeling ofP. cariniiin humans asP. jirovecii,[9][22]which is why both names still appear in publications. However, only the nameP. jiroveciiis used exclusively for the human pathogen, whereas the nameP. cariniihas had a broader application to many species.[23]Frenkel and those before him believed that allPneumocystiswereprotozoans,but soon afterwards evidence began accumulating thatPneumocystiswas a fungal genus. Recent studies show it to be an unusual, in some ways a primitive genus ofAscomycota,related to a group ofyeasts.[1]Every testedprimate,including humans, appears to have its own type ofPneumocystisthat is incapable of cross-infecting other host species and hasco-evolvedwith each species.[24]Currently, only five species have been formally named:P. jiroveciifrom humans,P. cariniias originally named from rats,P. murinafrom mice,[25]P. wakefieldiae[26][27]also from rats, andP. oryctolagifrom rabbits.[28]

Historical and even recent reports ofP. cariniifrom humans are based upon older classifications (still used by many, or those still debating the recognition of distinct species in the genusPneumocystis) which does not mean that the trueP. cariniifrom rats actually infects humans. In an intermediate classification system, the varioustaxain different mammals have been calledformae specialesor forms. For example, the human "form" was calledPneumocystis cariniif. [or f. sp.]hominis,while the original rat infecting form was calledPneumocystis cariniif. [or f. sp.]carinii.This terminology is still used by some researchers. The species ofPneumocystisoriginally seen by Chagas have not yet been named as distinct species.[9]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.[29][30]Currently, they are cryptic taxa.

References

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  1. ^abJames TY, Kauff F, Schoch CL, Matheny PB, Hofstetter V, Cox CJ, et al. (2006). "Reconstructing the early evolution of Fungi using a six-gene phylogeny".Nature.443(7113): 818–822.doi:10.1038/nature05110.PMID17051209.S2CID4302864.
  2. ^"see DPDx life-cycle diagram".Dpd.cdc.gov. Archived fromthe originalon 2013-03-18.Retrieved2013-03-26.
  3. ^abRichard S, Almeida JM, Cissé OH, Luraschi A, Nielsen O, Pagni M, Hauser PM (2018)."Functional and Expression Analyses of the Pneumocystis MAT Genes Suggest Obligate Sexuality through Primary Homothallism within Host Lungs".mBio.9(1).doi:10.1128/mBio.02201-17.PMC5821091.PMID29463658.
  4. ^Ponce CA, Gallo M, Bustamante R, Vargas SL (2010)."Pneumocystis colonization is highly prevalent in the autopsied lungs of the general population".Clin Infect Dis.50(3): 347–353.doi:10.1086/649868.PMID20047487.
  5. ^Stringer JR, Beard CB, Miller RF, Wakefield AE (2002)."A New Name for Pneumocystis from Humans and New Perspectives on the Host-Pathogen Relationship".Emerging Infectious Diseases.8(9): 891–6.doi:10.3201/eid0809.020096.PMC2732539.PMID12194762.
  6. ^Stringer JR, Beard CB, Miller RF (2009)."Spelling Pneumocystis jiroveci"(PDF).Emerging Infectious Diseases.15(3): 506a–506.doi:10.3201/eid1503.081060.PMC2681121.PMID19239784.
  7. ^"ICBN Recommendation 60C.1".If the personal name ends with a consonant (except -er),substantivalepithetsare formed by adding -i- (stem augmentation) plus the genitive inflection appropriate to the sex and number of the person(s) honoured (e.g.lecardiiforThéodore Lecard).
  8. ^"International Code of Nomenclature for algae, fungi, and plants".iapt-taxon.org.
  9. ^abcdRedhead SA, Cushion MT, Frenkel JK, Stringer JR (2006). "PneumocystisandTrypanosoma cruzi:nomenclature and typifications ".J Eukaryot Microbiol.53(1): 2–11.doi:10.1111/j.1550-7408.2005.00072.x.PMID16441572.S2CID38119833.
  10. ^"Pneumocystis Genome Project".Pgp.cchmc.org.Retrieved2013-03-26.
  11. ^Cisse, O. H; Pagni, M; Hauser, P. M (2012)."De Novo Assembly of the Pneumocystis jirovecii Genome from a Single Bronchoalveolar Lavage Fluid Specimen from a Patient".mBio.4(1): e00428–12.doi:10.1128/mBio.00428-12.PMC3531804.PMID23269827.
  12. ^Chagas C (1909). "Neue Trypanosomen".Vorläufige Mitteilung. Arch. Schiff. Tropenhyg.13:120–122.
  13. ^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.doi:10.1590/S0074-02761909000200008.
  14. ^Carini A. (1910). "Formas des eschizogonia doTrypanosoma lewisi".Soc Med Cir São Paulo.38(8).
  15. ^Delanoë P, Delanoë M (1912). "Sur les rapports des kystes de Carini du poumon des rats avec leTrypanosoma lewisi".Comptes Rendus de l'Académie des Sciences.155:658–61.
  16. ^van der Meer MG, Brug SL (1942). "Infection àPneumocystischez l'homme et chez les animaux ".Amer Soc Belge Méd Trop.22:301–9.
  17. ^Vanek J. (1951). "Atypicka (interstitiálni) pneumonie detí vyvolanáPneumocystis carinii(Atypical interstitial pneumonia of infants produced byPneumocystis carinii) ".Casop Lék Cesk.90:1121–4.
  18. ^Jírovec O. (1952). "Pneumocystis cariniipuvodce t. zv intertitialnich plasmocelularnich pneumonii kojencw (Pneumocystis carinii,the cause of interstitial plasmacellular pneumonia in neonates) ".CSL. Hyg. Epid. Mikrob.1:141.
  19. ^Vanek J, Jírovec O, Lukes J (1953). "Interstitial plasma cell pneumonia in infants".Annales Paediatrici.180(1): 1–21.PMID13051050.
  20. ^Gajdusek DC (1957). "Pneumocystis carinii;etiologic agent of interstitial plasma cell pneumonia of premature and young infants ".Pediatrics.19(4 Pt 1): 543–65.doi:10.1542/peds.19.4.543.PMID13419426.S2CID19507186.
  21. ^Frenkel JK (1976). "Pneumocystis jirovecin. sp. from man: morphology, physiology, and immunology in relation to pathology ".Natl Cancer Inst Monogr.43:13–27.PMID828240.
  22. ^Gigliotti F (2005)."Pneumocystis carinii:has the name really been changed? ".Clin Infect Dis.41(12): 1752–5.doi:10.1086/498150.PMID16288399.
  23. ^Hawksworth DL (2007). "Responsibility in naming pathogens: the case of Pneumocystis jiroveci, the causal agent of pneumocystis pneumonia".Lancet Infect. Dis.7(1): 3–5.doi:10.1016/S1473-3099(06)70663-6.PMID17182335.
  24. ^Hugot J, Demanche C, Barriel V, Dei-Cas E, Guillot J (2003)."Phylogenetic systematics and evolution of primate-derivedPneumocystisbased on mitochondrial or nuclear DNA sequence comparison ".Syst Biol.52(6): 735–744.doi:10.1080/10635150390250893.PMID14668114.
  25. ^Keely S, Fischer J, Cushion M, Stringer J (2004)."Phylogenetic identification ofPneumocystis murinasp. nov., a new species in laboratory mice ".Microbiology.150(Pt 5): 1153–65.doi:10.1099/mic.0.26921-0.PMID15133075.
  26. ^Cushion MT, Keely SP, Stringer JR (2004). "Molecular and phenotypic description of Pneumocystis wakefieldiae sp. nov., a new species in rats".Mycologia.96(3): 429–438.doi:10.2307/3762163.JSTOR3762163.PMID21148866.
  27. ^Cushion MT, Keely SP, Stringer JR (2005). "Validation of the name Pneumocystis wakefieldiae".Mycologia.97:268.doi:10.3852/mycologia.97.1.268.
  28. ^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 Microbiol. Rev.30(6): 853–871.doi:10.1111/j.1574-6976.2006.00037.x.PMID17064284.
  29. ^Aliouat-Denis, C-M.; et al. (2008). "Pneumocystisspecies, co-evolution and pathogenic power ".Infection, Genetics and Evolution.8(5): 708–726.doi:10.1016/j.meegid.2008.05.001.PMID18565802.
  30. ^Demanche C, et al. (2001)."Phylogeny of Pneumocystis carinii from 18 Primate Species Confirms Host Specificity and Suggests Coevolution".J. Clin. Microbiol.39(6): 2126–2133.doi:10.1128/JCM.39.6.2126-2133.2001.PMC88100.PMID11376046.
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