Histoplasma capsulatum: Difference between revisions

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__NOTOC__
__NOTOC__
{{Histoplasmosis}}
{{Histoplasmosis}}
{{Taxobox
| image = Histoplasma pas-d.jpg
| image_width = 250px
| image_caption = ''Histoplasma'' (bright red, small, circular). PAS diastase stain
| regnum = [[Fungi]]
| divisio = [[Ascomycota]]
| classis = [[Eurotiomycetes]]
| ordo = [[Onygenales]]
| familia = Ajellomycetaceae
| genus = '''''Histoplasma'''''
| genus_authority =  Samuel Taylor Darling (1906)
| type_species = ''Histoplasma capsulatum''
| type_species_authority = Darling (1906)
| subdivision_ranks = Species
| subdivision =''Histoplasma capsulatum''<br>
''Histoplasma duboisii''
}}
{{About0|Histoplasmosis}}
{{About0|Histoplasmosis}}
{{CMG}} {{AE}} {{SSK}}
{{CMG}} {{AE}} {{SSK}}


'''''Histoplasma''''' is a [[genus]] of [[dimorphic fungi]] commonly found in bird and bat [[feces|fecal]] material.<ref name=Baron>{{cite book | author = McGinnis MR, Tyring SK | title = Introduction to Mycology. ''In:'' Baron's Medical Microbiology (Baron S ''et al.'', eds.)| edition = 4th | publisher = Univ of Texas Medical Branch | year = 1996 | id = [http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mmed.section.3910#3919 (via NCBI Bookshelf)] ISBN 0-9631172-1-1 }}</ref> ''Histoplasma'' contains a few species, including—''H. capsulatum''—the causative agent of [[histoplasmosis]];<ref name=Sherris>{{cite book | author = Ryan KJ; Ray CG (editors) | title = Sherris Medical Microbiology | edition = 4th | publisher = McGraw Hill | year = 2004 | isbn = 0-8385-8529-9 }}</ref> and ''Histoplasma capsulatum var. farciminosum'' (old term, ''Histoplasma farciminosum''), causing [[Equine Lymphangitis|epizootic lymphangitis]] in horses.<ref>OIE ''Manual of Diagnostic Tests and Vaccines for Terrestrial Animals'' 2004 Chapter 2.5.13, [http://www.oie.int/eng/normes/mmanual/A_00091.htm]</ref> ''Histoplasma capsulatum'' is most prevalent in the [[Ohio]] and [[Mississippi River]] valleys. It was discovered by [[Samuel Taylor Darling]] in 1906.
== Overview ==
'''''Histoplasma capsulatum''''' is a [[dimorphic fungi|fungus]] commonly found in bird and bat [[feces|fecal]] material and is the causative agent of [[histoplasmosis]].<ref name="Baron">{{cite book | author = McGinnis MR, Tyring SK | title = Introduction to Mycology. ''In:'' Baron's Medical Microbiology (Baron S ''et al.'', eds.)| edition = 4th | publisher = Univ of Texas Medical Branch | year = 1996 | id = [http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mmed.section.3910#3919 (via NCBI Bookshelf)] ISBN 0-9631172-1-1 }}</ref> It belongs to the recently recognized fungal family Ajellomycetaceae. It is [[Dimorphic Fungi|dimorphic]] and switches from a mold-like (filamentous) growth form in the natural habitat to a small budding [[yeast]] form in the warm-blooded animal host. It is most prevalent in the [[Ohio]] and Mississippi River valleys.


==Growth and morphology==
==Growth and morphology==
''Histoplasma capsulatum'' is an ascomycetous fungus closely related to ''[[Blastomyces dermatitidis]]''. It is potentially sexual, and its sexual state, ''Ajellomyces capsulatus'', can readily be produced in culture, though it has not been directly observed in nature. As mentioned above, ''H. capsulatum'' groups with ''B. dermatitidis'' and the [[South America]]n pathogen ''[[Paracoccidioides brasiliensis]]'' in the recently recognized fungal family [[Ajellomycetaceae]].<ref name=untereiner2002 /><ref name=untereiner2004 /> It is dimorphic and switches from a mould-like (filamentous) growth form in the natural habitat to a small budding [[yeast]] form in the warm-blooded animal host.
* ''Histoplasma capsulatum'' is an ascomycetous fungus.
 
* It is [[Dimorphic Fungi|dimorphic]] and switches from a mold-like (filamentous) growth form in the natural habitat to a small budding [[yeast]] form in the host.
''Histoplasma capsulatum'' has two mating types "+" and "–", as with ''B. dermatitidis''. The great majority of North American isolates belong to a single genetic type<ref name= karimi2002 /><ref name=kasuga2003 /> but a study of multiple genes suggests a recombining, sexual population.<ref name=kasuga2003 /> A recent analysis has suggested that the prevalent [[North America]]n genetic type and a less common type should be considered separate phylogenetic species, distinct from ''H. capsulatum'' isolates obtained in Central and South America and other parts of the world. These entities are temporarily designated NAm1 (the rare type, which includes a famous experimental isolate designated "the Downs strain") and NAm2 (the common type).<ref name=kasuga2003 /> There is as yet no well established clinical or geographic distinction among these two genetic groups.  
* It is potentially sexual, and its sexual state, ''Ajellomyces capsulatus'', can readily be produced in culture, though it has not been directly observed in nature.  
 
* ''H. capsulatum'' groups with ''[[Blastomyces dermatitidis|B. dermatitidis]]'' and the South American pathogen ''[[Paracoccidioides brasiliensis]]'' in the recently recognized fungal family Ajellomycetaceae.<ref name="untereiner2002">{{cite journal|last1=Untereiner|first1=W.A.|last2=Scott|first2=J.A.|last3=Naveau|first3=F.A.|last4=Bachewich|first4=J.|title=Phylogeny of Ajellomyces, Polytolypa and Spiromastix (Onygenaceae) inferred from rDNA sequence and non-molecular data|journal=Studies in Mycology|date=2002|volume=47|pages=25-35}}</ref><ref name="untereiner2004">{{cite journal|last1=Untereiner|first1=WA|last2=Scott|first2=JA|last3=Naveau|first3=FA|last4=Sigler|first4=L|last5=Bachewich|first5=J|last6=Angus|first6=A|title=The Ajellomycetaceae, a new family of vertebrate-associated Onygenales.|journal=Mycologia|date=2004|volume=96|issue=4|pages=812-821|pmid=21148901}}</ref>
In its asexual form, the fungus grows as a colonial microfungus strongly similar in macromorphology to ''B. dermatitidis''. A microscopic examination shows a marked distinction: ''H. capsulatum'' produces two types of conidia, globose macroconidia, 8–15&nbsp;µm, with distinctive tuberculate or finger-like cell wall ornamentation, and ovoid microconidia, 2–4&nbsp;µm, which appear smooth or finely roughened. It is not clear whether one or both of these conidial types is more important than the other as the principal main infectious particles. They form on individual short stalks and readily become airborne when the colony is disturbed. Ascomata of the sexual state are 80–250&nbsp;µm, and are very similar in appearance and anatomy to those described above for ''B. dermatitidis''. The ascospores are similarly minute, averaging 1.5&nbsp;µm.
* ''Histoplasma capsulatum'' has two mating types "+" and "–", as with ''[[Blastomyces dermatitidis|B. dermatitidis]]''.  
 
* In its asexual form, the fungus grows as a colonial microfungus strongly similar in macromorphology to ''[[Blastomyces dermatitidis|B. dermatitidis]]''.  
The budding yeast cells formed in infected tissues are small (ca. 2–4&nbsp;µm) and are characteristically seen forming in clusters within phagocytic cells, including [[histiocyte]]s and other macrophages, as well as monocytes. An [[Africa]]n phylogenetic species, ''[[Histoplasma duboisii|H. duboisii]]'', often but not always forms larger yeast cells to 15&nbsp;µm.
* A [[microscopic examination]] shows a marked distinction: ''H. capsulatum'' produces two types of [[conidia]], globose macroconidia, 8–15&nbsp;µm, with distinctive tuberculate or finger-like cell wall ornamentation, and ovoid microconidia, 2–4&nbsp;µm, which appear smooth or finely roughened.  
* It is not clear whether one or both of these conidial types is more important than the other as the principal main infectious particles.  
* They form on individual short stalks and readily become [[Airborne transmission|airborne]] when the colony is disturbed.  
* Ascomata of the sexual state are 80–250&nbsp;µm, and are very similar in appearance and anatomy to those described above for ''B. dermatitidis''. The ascospores are similarly minute, averaging 1.5&nbsp;µm.
* The budding yeast cells formed in infected tissues are small (ca. 2–4&nbsp;µm) and are characteristically seen forming in clusters within [[Phagocytosis|phagocytic]] cells, including [[histiocyte]]s and other macrophages, as well as monocytes.  


==Geographic distribution==
==Geographic distribution==
The endemic zones of ''H. capsulatum'' can be roughly divided into core areas, where the fungus occurs widely in soil or on vegetation contaminated by bird droppings or equivalent organic inputs, and peripheral areas, where the fungus occurs relatively rarely in association with soil but is still found abundantly in heavy accumulations of bat or bird [[guano]] in enclosed spaces such as caves, buildings, and hollow trees. The principal core area for this species includes the valleys of the [[Mississippi River|Mississippi]], [[Ohio River|Ohio]] and [[Potomac River|Potomac]] rivers in the USA as well as a wide span of adjacent areas extending from [[Kansas]], [[Illinois]], [[Indiana]] and [[Ohio]] in the north to [[Mississippi]], [[Louisiana]] and [[Texas]] in the south.<ref name=kwon-chung1992 /><ref name=chamany2004 /><ref name=stobierski1996 /> In some areas, such as [[Kansas City]], skin testing with the histoplasmin antigen preparation shows that 80–90&nbsp;% of the resident population have an antibody reaction to H. capsulatum, probably indicating prior subclinical infection.<ref name=kwon-chung1992 /> Northern U.S. states such as [[Minnesota]], [[Michigan]], New York and [[Vermont]] are peripheral areas for histoplasmosis, but have scattered counties where 5–19&nbsp;% of lifetime residents show exposure to ''H. capsulatum''. One [[New York]] county, St. Lawrence county (across the [[St. Lawrence River]] from the [[Cornwall, Ontario|Cornwall]]– [[Preston, Ontario|Preston]] – [[Brockville, Ontario|Brockville]] area of [[Ontario, Canada]]) shows exposures over 20&nbsp;%.<ref name=kwon-chung1992 />
* The endemic zones of ''H. capsulatum'' can be roughly divided into core areas, where the [[fungus]] occurs widely in soil or on vegetation contaminated by bird droppings or equivalent organic inputs, and peripheral areas, where the fungus occurs relatively rarely in association with soil but is still found abundantly in heavy accumulations of bat or bird guano in enclosed spaces such as caves, buildings, and hollow trees.  
* The principal core area for this species includes the valleys of the Mississippi, Ohio and Potomac rivers in the USA as well as a wide span of adjacent areas extending from Kansas, Illinois, Indiana and Ohio in the north to Mississippi, Louisiana and Texas in the south.<ref name="kwon-chung1992">{{cite book|last1=Kwon-Chung|first1=K. June|last2=Bennett|first2=Joan E.|title=Medical mycology|year=1992|publisher=Lea & Febiger|location=Philadelphia|isbn=0812114639}}</ref><ref name="chamany2004">{{cite journal|last1=Chamany|first1=S|last2=Mirza|first2=SA|last3=Fleming|first3=JW|last4=Howell|first4=JF|last5=Lenhart|first5=SW|last6=Mortimer|first6=VD|last7=Phelan|first7=MA|last8=Lindsley|first8=MD|last9=Iqbal|first9=NJ|last10=Wheat|first10=LJ|last11=Brandt|first11=ME|last12=Warnock|first12=DW|last13=Hajjeh|first13=RA|title=A large histoplasmosis outbreak among high school students in Indiana, 2001.|journal=The Pediatric infectious disease journal|date=2004|volume=23|issue=10|pages=909-14|pmid=15602189}}</ref><ref name="stobierski1996">{{cite journal|last1=Stobierski|first1=MG|last2=Hospedales|first2=CJ|last3=Hall|first3=WN|last4=Robinson-Dunn|first4=B|last5=Hoch|first5=D|last6=Sheill|first6=DA|title=Outbreak of histoplasmosis among employees in a paper factory--Michigan, 1993.|journal=Journal of Clinical Microbiology|date=1996|volume=34|issue=5|pages=1220-1223|pmid=8727906}}</ref>  
* In some areas, such as Kansas City, skin testing with the histoplasmin antigen preparation shows that 80–90&nbsp;% of the resident population have an antibody reaction to H. capsulatum, probably indicating prior subclinical infection.<ref name="kwon-chung1992" />  
* Northern U.S. states such as Minnesota, Michigan, New York and Vermont are peripheral areas for histoplasmosis, but have scattered counties where 5–19&nbsp;% of lifetime residents show exposure to ''H. capsulatum''.


The distribution of ''H. capsulatum'' in Canada is not as well documented as in the US. The St. Lawrence Valley is probably the best known endemic region based both on case reports and on a number of skin test reaction studies that were done between 1945 and 1970. The [[Montreal]] area is a particularly well documented endemic focus, not just in the agricultural regions surrounding the city<ref name=guy1949b /> but also within the city itself.<ref name=leznoff1969 /> The [[Mount Royal]] area in central Montreal, especially the north and east sides of Mt. Royal Park, showed exposure rates between 20 and 50&nbsp;% in schoolchildren<ref name=leznoff1969 /> and locally lifetime-resident university students.<ref name=maceachern1971 /> A particularly high rate of 79.3&nbsp;% exposure was shown in [[St. Thomas, Ontario]], south of [[London, Ontario]], after 7 local residents had died of histoplasmosis in 1957<ref name=haggar1957 /> Based on numerous small regional studies, histoplasmin skin test reactors form ca. 10–50&nbsp;% of the population in much of southern Ontario and in Quebec’s St. Lawrence Valley, ca. 5&nbsp;% in southern Manitoba and some northerly parts of [[Quebec]] (e.g., [[Abitibi-Témiscamingue]]), and ca. 1&nbsp;% in [[Nova Scotia]].<ref name=maceachern1971 /><ref name=haggar1957 /><ref name=rostocka1966 /><ref name=hoff1970 /><ref name=mochi1952 /> Exposure of aboriginal Canadians occurs remarkably far north in Quebec,<ref name=guy1949a /><ref name=schaefer1966 /> but has not been reported in similar boreal biogeoclimatic zones in many other parts of Canada. Recently and remarkably, a cluster of four indigenously acquired cases of histoplasmosis was shown to be associated with a golf course in suburban [[Edmonton, Alberta]].<ref name=anderson2006 /> Examination suggested that local soil was the source.
==Ecology==
 
* ''Histoplasma capsulatum'' appears to be strongly associated with the droppings of certain bird species as well as bats.<ref name="kwon-chung1992" />  
==Ecology and epidemiology==
* A mixture of these droppings and certain soil types is particularly conducive to proliferation.  
''Histoplasma capsulatum'' appears to be strongly associated with the droppings of certain bird species as well as bats.<ref name=kwon-chung1992 /> A mixture of these droppings and certain soil types is particularly conducive to proliferation. In highly endemic areas there is a strong association with soil under and around chicken houses, and with areas where soil or vegetation has become heavily contaminated with faecal material deposited by flocking birds such as [[starling]]s and [[New_World_blackbird|blackbird]]s. Bird roosting areas that are ''Histoplasma''-free appear to be lower in nitrogen, phosphorus, organic matter and moisture than contaminated roosting areas.<ref name=kwon-chung1992 /> Interestingly, the guano of gulls and other colonially nesting water-associated birds is rarely connected to histoplasmosis.<ref name=waldman1983 /> Bat dwellings, including caves, attics and hollow trees, are classic ''H. capsulatum'' habitats.<ref name=kwon-chung1992 /><ref name=rippon1988 /> Histoplasmosis outbreaks are typically associated with cleaning guano accumulations or clearing guano-covered vegetation, or with exploration of bat caves. In addition, however, outbreaks may be associated with wind-blown dust liberated by construction projects in endemic areas: a classic outbreak is one associated with intense construction activity, including subway construction, in Montreal in 1963.<ref name=leznoff1964 />
* In highly endemic areas there is a strong association with soil under and around chicken houses, and with areas where soil or vegetation has become heavily contaminated with fecal material deposited by flocking birds such as starlings and blackbirds.  
 
* Bird roosting areas that are ''Histoplasma''-free appear to be lower in nitrogen, phosphorus, organic matter and moisture than contaminated roosting areas.<ref name="kwon-chung1992" />  
As with blastomycosis, a good understanding of the precise ecological affinities of ''H. capsulatum'' is greatly complicated by the difficulty of isolating the fungus directly from nature. Again, the mouse passage procedure originally devised by Emmons<ref name=emmons1961 /> must be used. A direct PCR technique for detection of ''H. capsulatum'' in soil has been published.<ref name=reid1999 /> As mentioned above, ''H. capsulatum'' appears particularly likely to cause clinical disease in young children, persons working in sites contaminated by conducive bird or bat droppings, persons exposed to construction dust raised from contaminated sites, immunocompromised patients, and emphysema sufferers. Elimination of the agent from contaminated soils typically involves the use of toxic fumigants with limited success.<ref name=ajello1983 />
* The guano of gulls and other colonially nesting water-associated birds is rarely connected to histoplasmosis.<ref name="waldman1983">{{cite journal|last1=Waldman|first1=RJ|last2=England|first2=AC|last3=Tauxe|first3=R|last4=Kline|first4=T|last5=Weeks|first5=RJ|last6=Ajello|first6=L|last7=Kaufman|first7=L|last8=Wentworth|first8=B|last9=Fraser|first9=DW|title=A winter outbreak of acute histoplasmosis in northern Michigan.|journal=American Journal of Epidemiology|date=1983|volume=117|issue=1|pages=68-75|pmid=6823954}}</ref>  
* Bat dwellings, including caves, attics and hollow trees, are classic ''H. capsulatum'' habitats.<ref name="kwon-chung1992" /><ref name="rippon1988">{{cite book|last=Rippon|first=John Willard|title=Medical mycology: the pathogenic fungi and the pathogenic actinomycetes|year=1988|publisher=Saunders|location=Philadelphia, PA|isbn=0721624448|edition=3rd}}</ref>  
* Histoplasmosis outbreaks are typically associated with cleaning guano accumulations or clearing guano-covered vegetation, or with exploration of bat caves.  
* In addition, however, outbreaks may be associated with wind-blown dust liberated by construction projects in endemic areas: a classic outbreak is one associated with intense construction activity, including subway construction, in Montreal in 1963.<ref name="leznoff1964">{{cite journal|last1=Leznoff|first1=A|last2=Frank|first2=H|last3=Telner|first3=P|last4=Rosensweig|first4=J|last5=Brandt|first5=JL|title=Histoplasmosis in Montreal during the fall of 1963, with observations on erythema multiforme.|journal=Canadian Medical Association journal|date=1964|volume=91|pages=1154-1160|pmid=14226089}}</ref>
* As with blastomycosis, a good understanding of the precise ecological affinities of ''H. capsulatum'' is greatly complicated by the difficulty of isolating the fungus directly from nature.


==Gallery==
==Gallery==
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</gallery>
</gallery>
==References==
==References==
{{reflist|refs=
{{reflist|2}}


<ref name=ajello1983>{{cite book|last1=Ajello|first1=L.|last2=Weeks|first2=R.J.|editor1-last=DiSalvo|editor1-first=Arthur F.|title=Occupational mycoses|date=1983|publisher=Lea and Febiger|location=Philadelphia, Pa.|isbn=9780812108859|pages=229-238|chapter=Soil decontamination and other control measures}}</ref>
<ref name=anderson2006>{{cite journal|last1=Anderson|first1=Heather|last2=Honish|first2=Lance|last3=Taylor|first3=Geoff|last4=Johnson|first4=Marcia|last5=Tovstiuk|first5=Chrystyna|last6=Fanning|first6=Anne|last7=Tyrrell|first7=Gregory|last8=Rennie|first8=Robert|last9=Jaipaul|first9=Joy|last10=Sand|first10=Crystal|last11=Probert|first11=Steven|title=Histoplasmosis Cluster, Golf Course, Canada|journal=Emerging Infectious Diseases|date=2006|volume=12|issue=1|pages=163–165|doi=10.3201/eid1201.051083}}</ref>
<ref name=chamany2004>{{cite journal|last1=Chamany|first1=S|last2=Mirza|first2=SA|last3=Fleming|first3=JW|last4=Howell|first4=JF|last5=Lenhart|first5=SW|last6=Mortimer|first6=VD|last7=Phelan|first7=MA|last8=Lindsley|first8=MD|last9=Iqbal|first9=NJ|last10=Wheat|first10=LJ|last11=Brandt|first11=ME|last12=Warnock|first12=DW|last13=Hajjeh|first13=RA|title=A large histoplasmosis outbreak among high school students in Indiana, 2001.|journal=The Pediatric infectious disease journal|date=2004|volume=23|issue=10|pages=909-14|pmid=15602189}}</ref>
<ref name=emmons1961>{{cite journal|last1=Emmons|first1=C.W.|title=Isolation of Histoplasma capsulatum from soil in Washington, D.C.|journal=Public Health Reports|date=1961|volume=76|issue=591-596}}</ref>
<ref name=guy1949a>{{cite journal|last1=Guy|first1=R|last2=Panisset|first2=M|last3=Frappier|first3=A|title=Histoplasmin sensitivity; a brief study of the incidence of hypersensitivity to histoplasmin in an Indian tribe of northern Quebec.|journal=Canadian journal of public health = Revue canadienne de sante publique|date=1949|volume=40|issue=7|pages=306-309|pmid=18133141}}</ref>
<ref name=guy1949b>{{cite journal|last1=Guy|first1=R|last2=Roy|first2=O|title=Histoplasmin sensitivity; preliminary observations in a group of school children in the Province of Quebec.|journal=Canadian journal of public health = Revue canadienne de sante publique|date=1949|volume=40|issue=2|pages=68-71|pmid=18113223}}</ref>
<ref name=haggar1957>{{cite journal|last1=Haggar|first1=R.A|last2=Brown|first2=E.L.|last3=Toplack|first3=N.J.|title=Histoplasmosis in South Western Ontario|journal=Canadian Medical Association Journal|date=1957|volume=77|pages=855-861}}</ref>
<ref name=hajjeh1995>{{cite journal|last1=Hajjeh|first1=RA|title=Disseminated histoplasmosis in persons infected with human immunodeficiency virus.|journal=Clinical infectious diseases : an official publication of the Infectious Diseases Society of America|date=1995|volume=21 Suppl 1|pages=S108-10|pmid=8547497}}</ref>
<ref name=hoff1970>{{cite journal|last1=Hoff|first1=B.|last2=Fogle|first2=B.|title=Case report. Histoplasmosis in a dog|journal=Canadian Veterinary Journal|date=1970|volume=11|issue=7|pages=145–148}}</ref>
<ref name=karimi2002>{{cite journal|last1=Karimi|first1=K|last2=Wheat|first2=LJ|last3=Connolly|first3=P|last4=Cloud|first4=G|last5=Hajjeh|first5=R|last6=Wheat|first6=E|last7=Alves|first7=K|last8=Lacaz Cd Cda|first8=S|last9=Keath|first9=E|title=Differences in histoplasmosis in patients with acquired immunodeficiency syndrome in the United States and Brazil.|journal=The Journal of infectious diseases|date=1 December 2002|volume=186|issue=11|pages=1655-1660|doi=10.1086/345724|pmid=12447743}}</ref>
<ref name=kasuga2003>{{cite journal|last1=Kasuga|first1=T|last2=White|first2=TJ|last3=Koenig|first3=G|last4=McEwen|first4=J|last5=Restrepo|first5=A|last6=Castañeda|first6=E|last7=Da Silva Lacaz|first7=C|last8=Heins-Vaccari|first8=EM|last9=De Freitas|first9=RS|last10=Zancopé-Oliveira|first10=RM|last11=Qin|first11=Z|last12=Negroni|first12=R|last13=Carter|first13=DA|last14=Mikami|first14=Y|last15=Tamura|first15=M|last16=Taylor|first16=ML|last17=Miller|first17=GF|last18=Poonwan|first18=N|last19=Taylor|first19=JW|title=Phylogeography of the fungal pathogen Histoplasma capsulatum.|journal=Molecular ecology|date=2003|volume=12|issue=12|pages=3383-401|pmid=14629354}}</ref>
<ref name=kauffman2007>{{cite journal|last1=Kauffman|first1=C. A.|title=Histoplasmosis: a Clinical and Laboratory Update|journal=Clinical Microbiology Reviews|date=2007|volume=20|issue=1|pages=115–132|doi=10.1128/CMR.00027-06}}</ref>
<ref name=kwon-chung1992>{{cite book|last1=Kwon-Chung|first1=K. June|last2=Bennett|first2=Joan E.|title=Medical mycology|year=1992|publisher=Lea & Febiger|location=Philadelphia|isbn=0812114639}}</ref>
<ref name=leznoff1969>{{cite journal|last1=Leznoff|first1=A|last2=Frank|first2=H|last3=Taussig|first3=A|last4=Brandt|first4=JL|title=The focal distribution of histoplasmosis in Montreal.|journal=Canadian journal of public health = Revue canadienne de sante publique|date=1969|volume=60|issue=8|pages=321-5|pmid=5806145}}</ref>
<ref name=leznoff1964>{{cite journal|last1=Leznoff|first1=A|last2=Frank|first2=H|last3=Telner|first3=P|last4=Rosensweig|first4=J|last5=Brandt|first5=JL|title=Histoplasmosis in Montreal during the fall of 1963, with observations on erythema multiforme.|journal=Canadian Medical Association journal|date=1964|volume=91|pages=1154-1160|pmid=14226089}}</ref>
<ref name=maceachern1971>{{cite journal|last1=MacEachern|first1=EJ|last2=McDonald|first2=JC|title=Histoplasmin sensitivity in McGill University students.|journal=Canadian journal of public health = Revue canadienne de sante publique|date=1971|volume=62|issue=5|pages=415-422|pmid=5137623}}</ref>
<ref name=mochi1952>{{cite journal|last1=Mochi|first1=A|last2=Edwards|first2=PQ|title=Geographical distribution of histoplasmosis and histoplasmin sensitivity.|journal=Bulletin of the World Health Organization|date=1952|volume=5|issue=3|pages=259-291|pmid=14935779}}</ref>
<ref name=reid1999>{{cite journal|last1=Reid|first1=TM|last2=Schafer|first2=MP|title=Direct detection of Histoplasma capsulatum in soil suspensions by two-stage PCR.|journal=Molecular and Cellular Probes|date=1999|volume=13|issue=4|pages=269-273|pmid=10441199}}</ref>
<ref name=rippon1988>{{cite book|last=Rippon|first=John Willard|title=Medical mycology: the pathogenic fungi and the pathogenic actinomycetes|year=1988|publisher=Saunders|location=Philadelphia, PA|isbn=0721624448|edition=3rd}}</ref>
<ref name=rostocka1966>{{cite journal|last1=Rostocka|first1=M|last2=Hiltz|first2=JE|title=Histoplasmin skin sensitivity in Nova Scotia.|journal=Canadian journal of public health = Revue canadienne de sante publique|date=1966|volume=57|issue=9|pages=413-418|pmid=5981243}}</ref>
<ref name=schaefer1966>{{cite journal|last1=Schaefer|first1=O|title=Pulmonary miliary calcification and histoplasmin sensitivity in Canadian eskimos.|journal=Canadian journal of public health = Revue canadienne de sante publique|date=1966|volume=57|issue=9|pages=410-418|pmid=5977447}}</ref>
<ref name=stobierski1996>{{cite journal|last1=Stobierski|first1=MG|last2=Hospedales|first2=CJ|last3=Hall|first3=WN|last4=Robinson-Dunn|first4=B|last5=Hoch|first5=D|last6=Sheill|first6=DA|title=Outbreak of histoplasmosis among employees in a paper factory--Michigan, 1993.|journal=Journal of Clinical Microbiology|date=1996|volume=34|issue=5|pages=1220-1223|pmid=8727906}}</ref>
<ref name=untereiner2002>{{cite journal|last1=Untereiner|first1=W.A.|last2=Scott|first2=J.A.|last3=Naveau|first3=F.A.|last4=Bachewich|first4=J.|title=Phylogeny of Ajellomyces, Polytolypa and Spiromastix (Onygenaceae) inferred from rDNA sequence and non-molecular data|journal=Studies in Mycology|date=2002|volume=47|pages=25-35}}</ref>
<ref name=untereiner2004>{{cite journal|last1=Untereiner|first1=WA|last2=Scott|first2=JA|last3=Naveau|first3=FA|last4=Sigler|first4=L|last5=Bachewich|first5=J|last6=Angus|first6=A|title=The Ajellomycetaceae, a new family of vertebrate-associated Onygenales.|journal=Mycologia|date=2004|volume=96|issue=4|pages=812-821|pmid=21148901}}</ref>
<ref name=waldman1983>{{cite journal|last1=Waldman|first1=RJ|last2=England|first2=AC|last3=Tauxe|first3=R|last4=Kline|first4=T|last5=Weeks|first5=RJ|last6=Ajello|first6=L|last7=Kaufman|first7=L|last8=Wentworth|first8=B|last9=Fraser|first9=DW|title=A winter outbreak of acute histoplasmosis in northern Michigan.|journal=American Journal of Epidemiology|date=1983|volume=117|issue=1|pages=68-75|pmid=6823954}}</ref>
}}




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style="background:#Template:Taxobox colour;"|Template:Taxobox name
Histoplasma (bright red, small, circular). PAS diastase stain
Histoplasma (bright red, small, circular). PAS diastase stain
style="background:#Template:Taxobox colour;" | Scientific classification
Kingdom: Fungi
Division: Ascomycota
Class: Eurotiomycetes
Order: Onygenales
Family: Ajellomycetaceae
Genus: Histoplasma
Samuel Taylor Darling (1906)
Type species
Histoplasma capsulatum
Darling (1906)
Species

Histoplasma capsulatum
Histoplasma duboisii

This page is about microbiologic aspects of the organism(s).  For clinical aspects of the disease, see Histoplasmosis.

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Serge Korjian M.D.

Overview

Histoplasma capsulatum is a fungus commonly found in bird and bat fecal material and is the causative agent of histoplasmosis.[1] It belongs to the recently recognized fungal family Ajellomycetaceae. It is dimorphic and switches from a mold-like (filamentous) growth form in the natural habitat to a small budding yeast form in the warm-blooded animal host. It is most prevalent in the Ohio and Mississippi River valleys.

Growth and morphology

  • Histoplasma capsulatum is an ascomycetous fungus.
  • It is dimorphic and switches from a mold-like (filamentous) growth form in the natural habitat to a small budding yeast form in the host.
  • It is potentially sexual, and its sexual state, Ajellomyces capsulatus, can readily be produced in culture, though it has not been directly observed in nature.
  • H. capsulatum groups with B. dermatitidis and the South American pathogen Paracoccidioides brasiliensis in the recently recognized fungal family Ajellomycetaceae.[2][3]
  • Histoplasma capsulatum has two mating types "+" and "–", as with B. dermatitidis.
  • In its asexual form, the fungus grows as a colonial microfungus strongly similar in macromorphology to B. dermatitidis.
  • A microscopic examination shows a marked distinction: H. capsulatum produces two types of conidia, globose macroconidia, 8–15 µm, with distinctive tuberculate or finger-like cell wall ornamentation, and ovoid microconidia, 2–4 µm, which appear smooth or finely roughened.
  • It is not clear whether one or both of these conidial types is more important than the other as the principal main infectious particles.
  • They form on individual short stalks and readily become airborne when the colony is disturbed.
  • Ascomata of the sexual state are 80–250 µm, and are very similar in appearance and anatomy to those described above for B. dermatitidis. The ascospores are similarly minute, averaging 1.5 µm.
  • The budding yeast cells formed in infected tissues are small (ca. 2–4 µm) and are characteristically seen forming in clusters within phagocytic cells, including histiocytes and other macrophages, as well as monocytes.

Geographic distribution

  • The endemic zones of H. capsulatum can be roughly divided into core areas, where the fungus occurs widely in soil or on vegetation contaminated by bird droppings or equivalent organic inputs, and peripheral areas, where the fungus occurs relatively rarely in association with soil but is still found abundantly in heavy accumulations of bat or bird guano in enclosed spaces such as caves, buildings, and hollow trees.
  • The principal core area for this species includes the valleys of the Mississippi, Ohio and Potomac rivers in the USA as well as a wide span of adjacent areas extending from Kansas, Illinois, Indiana and Ohio in the north to Mississippi, Louisiana and Texas in the south.[4][5][6]
  • In some areas, such as Kansas City, skin testing with the histoplasmin antigen preparation shows that 80–90 % of the resident population have an antibody reaction to H. capsulatum, probably indicating prior subclinical infection.[4]
  • Northern U.S. states such as Minnesota, Michigan, New York and Vermont are peripheral areas for histoplasmosis, but have scattered counties where 5–19 % of lifetime residents show exposure to H. capsulatum.

Ecology

  • Histoplasma capsulatum appears to be strongly associated with the droppings of certain bird species as well as bats.[4]
  • A mixture of these droppings and certain soil types is particularly conducive to proliferation.
  • In highly endemic areas there is a strong association with soil under and around chicken houses, and with areas where soil or vegetation has become heavily contaminated with fecal material deposited by flocking birds such as starlings and blackbirds.
  • Bird roosting areas that are Histoplasma-free appear to be lower in nitrogen, phosphorus, organic matter and moisture than contaminated roosting areas.[4]
  • The guano of gulls and other colonially nesting water-associated birds is rarely connected to histoplasmosis.[7]
  • Bat dwellings, including caves, attics and hollow trees, are classic H. capsulatum habitats.[4][8]
  • Histoplasmosis outbreaks are typically associated with cleaning guano accumulations or clearing guano-covered vegetation, or with exploration of bat caves.
  • In addition, however, outbreaks may be associated with wind-blown dust liberated by construction projects in endemic areas: a classic outbreak is one associated with intense construction activity, including subway construction, in Montreal in 1963.[9]
  • As with blastomycosis, a good understanding of the precise ecological affinities of H. capsulatum is greatly complicated by the difficulty of isolating the fungus directly from nature.

Gallery

  • Photomicrograph reveals some of the ultrastructural details exhibited by Histoplasma capsulatum fungal organisms that had been extracted from a Jamaican isolate, which included a number of tuberculate (knobby) spheroidal macroconidia, and diaphanous filamentous hyphae (800X). From Public Health Image Library (PHIL). [10]

    Photomicrograph reveals some of the ultrastructural details exhibited by Histoplasma capsulatum fungal organisms that had been extracted from a Jamaican isolate, which included a number of tuberculate (knobby) spheroidal macroconidia, and diaphanous filamentous hyphae (800X). From Public Health Image Library (PHIL). [10]

  • This Giemsa-stained photomicrograph reveals numerous Histoplasma capsulatum fungal organisms in their yeast-stage of development, which were seen in this liver tissue specimen, in this case of disseminated histoplasmosis. From Public Health Image Library (PHIL). [10]

    This Giemsa-stained photomicrograph reveals numerous Histoplasma capsulatum fungal organisms in their yeast-stage of development, which were seen in this liver tissue specimen, in this case of disseminated histoplasmosis. From Public Health Image Library (PHIL). [10]

References

  1. ↑ McGinnis MR, Tyring SK (1996). Introduction to Mycology. In: Baron's Medical Microbiology (Baron S et al., eds.) (4th ed.). Univ of Texas Medical Branch. (via NCBI Bookshelf) ISBN 0-9631172-1-1.
  2. ↑ Untereiner, W.A.; Scott, J.A.; Naveau, F.A.; Bachewich, J. (2002). "Phylogeny of Ajellomyces, Polytolypa and Spiromastix (Onygenaceae) inferred from rDNA sequence and non-molecular data". Studies in Mycology. 47: 25–35.
  3. ↑ Untereiner, WA; Scott, JA; Naveau, FA; Sigler, L; Bachewich, J; Angus, A (2004). "The Ajellomycetaceae, a new family of vertebrate-associated Onygenales". Mycologia. 96 (4): 812–821. PMID 21148901.
  4. ↑ 4.0 4.1 4.2 4.3 4.4 Kwon-Chung, K. June; Bennett, Joan E. (1992). Medical mycology. Philadelphia: Lea & Febiger. ISBN 0812114639.
  5. ↑ Chamany, S; Mirza, SA; Fleming, JW; Howell, JF; Lenhart, SW; Mortimer, VD; Phelan, MA; Lindsley, MD; Iqbal, NJ; Wheat, LJ; Brandt, ME; Warnock, DW; Hajjeh, RA (2004). "A large histoplasmosis outbreak among high school students in Indiana, 2001". The Pediatric infectious disease journal. 23 (10): 909–14. PMID 15602189.
  6. ↑ Stobierski, MG; Hospedales, CJ; Hall, WN; Robinson-Dunn, B; Hoch, D; Sheill, DA (1996). "Outbreak of histoplasmosis among employees in a paper factory--Michigan, 1993". Journal of Clinical Microbiology. 34 (5): 1220–1223. PMID 8727906.
  7. ↑ Waldman, RJ; England, AC; Tauxe, R; Kline, T; Weeks, RJ; Ajello, L; Kaufman, L; Wentworth, B; Fraser, DW (1983). "A winter outbreak of acute histoplasmosis in northern Michigan". American Journal of Epidemiology. 117 (1): 68–75. PMID 6823954.
  8. ↑ Rippon, John Willard (1988). Medical mycology: the pathogenic fungi and the pathogenic actinomycetes (3rd ed.). Philadelphia, PA: Saunders. ISBN 0721624448.
  9. ↑ Leznoff, A; Frank, H; Telner, P; Rosensweig, J; Brandt, JL (1964). "Histoplasmosis in Montreal during the fall of 1963, with observations on erythema multiforme". Canadian Medical Association journal. 91: 1154–1160. PMID 14226089.
  10. ↑ 10.0 10.1 "Public Health Image Library (PHIL)".


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