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| {{Taxobox
| | #REDIRECT [[Blastomyces dermatitidis]] |
| | name = ''Blastomyces''
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| | image = Blastomyces dermatitidis yeast form.jpeg
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| | image_caption = ''Blastomyces dermatitidis'', yeast form
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| | regnum = [[Fungi]]
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| | phylum = [[Ascomycota]]
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| | classis = [[Eurotiomycetes]]
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| | ordo = [[Onygenales]]
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| | familia = [[Ajellomycetaceae]]
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| | genus = ''Blastomyces''
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| }}
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| __NOTOC__
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| {{About0|Blastomycosis}}
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| {{Blastomycosis}}
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| {{CMG}}
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| ==Overview==
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| '''''Blastomyces dermatitidis''''' is the causal agent of [[blastomycosis]], an invasive and often serious fungal infection found occasionally in humans and other animals in regions where the fungus is endemic.<ref name=disalvo1992>{{cite book|last=DiSalvo|first=A.F.|title=Ecology of Blastomyces dermatitidis|year=1992|publisher=Plenum|pages=43–73|authorlink=Blastomycosis|editor=Al-Doory, Y., DiSalvo, A.F.}}</ref> The causal organism is a fungus living in soil and wet, decaying wood, often in an area close to a waterway such as a lake, river or stream.<ref name=disalvo1992>{{cite book|last=DiSalvo|first=A.F.|title=Ecology of Blastomyces dermatitidis|year=1992|publisher=Plenum|pages=43–73|authorlink=Blastomycosis|editor=Al-Doory, Y., DiSalvo, A.F.}}</ref> Indoor growth may also occur, for example, in accumulated debris in damp sheds or shacks. The fungus is endemic to parts of eastern North America, particularly boreal northern Ontario, southeastern Manitoba, Quebec south of the [[St. Lawrence River]], parts of the U.S. [[Appalachian Mountains|Appalachian mountains]] and interconnected eastern mountain chains, the west bank of [[Lake Michigan]], the state of [[Wisconsin]], and the entire [[Mississippi Valley]] including the valleys of some major tributaries such as the Ohio River. In addition, it occurs rarely in Africa both north and south of the [[Sahara Desert|Sahara desert]], as well as in the [[Arabian Peninsula]] and the Indian subcontinent. Though it has never been directly observed growing in nature, it is thought to grow there as a cottony white mold, similar to the growth seen in artificial culture at 25 °C. In an infected human or animal, however, it converts in growth form and becomes a large-celled budding yeast.<ref name=disalvo1992>{{cite book|last=DiSalvo|first=A.F.|title=Ecology of Blastomyces dermatitidis|year=1992|publisher=Plenum|pages=43–73|authorlink=Blastomycosis|editor=Al-Doory, Y., DiSalvo, A.F.}}</ref> Blastomycosis is generally readily treatable with systemic antifungal drugs once it is correctly diagnosed; however, delayed diagnosis is very common except in highly endemic areas.
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| ==Morphology and phylogeny==
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| ''Blastomyces dermatitidis'' is the causal agent of [[blastomycosis]], a potentially very serious disease that typically begins with a characteristically subtle pneumonia-like infection that may progress, after 1–6 months, to a disseminated phase that causes lesions to form in capillary beds throughout the body, most notably the skin, internal organs, central nervous system and bone marrow. ''Blastomyces dermatitidis'' is the name applied to the [[ascomycota|ascomycetous fungus]], ''Ajellomyces dermatitidis''. Recently an second species has been described in the genus ''Blastomyces'', ''B. gilchristii'', which subsumes certain strains previously assigned to ''B. dermatitidis''.<ref name=brown2013/> Despite widespread use, the genus ''Blastomyces'' is currently invalid under the International Code of Botanical Nomenclature.<ref name=peterson1998/> Along with two other important human-pathogenic fungi, ''[[Histoplasma capsulatum]]'', ''[[Paracoccidioides brasiliensis]]'' and ''[[Polytolypa hystricis]]'', species of ''Blastomyces ''belong to a recently recognized fungal family, the [[Ajellomycetaceae]].<ref name=untereiner2004/> The three principal pathogens in this family are all grouped physiologically as “[[dimorphic fungi]]”: fungi that switch from a mold-like (filamentous) growth form in the natural habitat to a yeast-like growth form in the warm-blooded animal host. ''Blastomyces dermatitidis'' itself is a sexual organism, occurring in nature as both a + mating type and a – mating type. This is epidemiologically important for two reasons: firstly, it implies that the organism will be genetically variable, potentially leading to variations in disease severity, treatment response and habitat preference; secondly, it implies that a suitable, stable habitat must exist for the complex process of sexual reproduction to take place. This habitat is as yet unknown. In its asexual form, the fungus grows as a typical colonial microfungus, comparable to ''[[Penicillium]] ''or ''[[Rhizopus]] ''mold forms commonly seen on mouldy bread.
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| In nature, the fungus forms a network of thread-like [[mycelium]] that penetrates the substratum on which it grows, and then after 3–5 days of growth begins to reproduce asexually with small (2–10 µm) [[conidia]] (asexual spores). These conidia are probably the main infectious particles produced by the fungus. They form on individual short stalks and readily become airborne when the colony is disturbed; their size places them well within the respirable size range for particles,<ref name=lippman2001/> meaning that they can deposit deeply in the lungs when inhaled. Sexual reproduction by the fungus requires the meeting of colonies of + and – [[mating type]], probably a relatively rare event, and results in the production of small ascomata (sexual fruiting bodies) 200–350 µm, looking, to the naked eye, similar to a woollen fuzz ball, and in microscopic view consisting of a layer of spiralling, springy guard hairs surrounding a fertile core in which groups of 8 [[ascospores]] (sexual spores) are produced in small round reproductive sacs (asci). The ascospores, at 1.5–2.0 µm, are among the smallest reproductive particles produced by fungi, and are within the respirable size range.<ref name=lippman2001/> The budding yeast cells seen in infected tissues and bodily fluids are generally relatively large (ca. 8–15 µm) and characteristically bud through a broad base or neck, making them highly recognizable to the pathologist. A small (“nanic”) form is rarely seen with cells under 6 µm.
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| ==Geographic distribution and variants==
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| One of the unexplained regularities of nature is that there are several fungi of different phylogenetic ancestry that show a similar pattern of existence: dimorphism (conversion from a filamentous form in the environment to a yeast form in warm-blooded host tissues), virulent pathogenesis (ability to cause a significant infection in an animal host that is otherwise in good health), pulmonary infectivity (infection mainly via the lungs) and sharply delimited endemism (occurrence in only a limited geographic range.). ''Blastomyces dermatitidis'' is one of these fungi; the others are ''[[Histoplasma capsulatum]]'', ''[[Paracoccidioides brasiliensis]]'', ''[[Coccidioides immitis]]'', ''[[Coccidioides posadassii|C. posadasii]]'' and ''[[Penicillium marneffei]]''.
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| The geographic range of ''B. dermatitidis'' is largely focused around the waterways of the St. Lawrence and Mississippi River systems of North America. There is a widely distributed and much republished, partially erroneous map that shows the U.S. portion of this range accurately, inclusive of occurrence in Minnesota, Wisconsin, Ohio, Kentucky, Arkansas, Tennessee, North and South Carolina, the Virginias, Mississippi, Louisiana, and a few regions of states adjacent to those named.<ref name=kwonchung1992/> The Canadian range of ''B. dermatitidis'' shows an abundance of blastomycosis in broad areas north and south of the St. Lawrence River in Quebec, as well as high endemicity along the north shore of [[Lake Erie]] and the low endemicity in southeastern corner of Manitoba. Though the Quebec distribution is reasonably accurate, the rest of Canada is strongly misrepresented. ''Blastomyces dermatitidis'' is absent or nearly so from the Lake Erie area, but occurs sporadically on the north shore of [[Lake Ontario]], including metropolitan Toronto,<ref name=lester2000/> and, most notably, has areas of high endemicity throughout northern Ontario.<ref name=kane1983/> Remarkably high incidence is noted for some parts of the Kenora area and climatologically similar areas of northwestern Ontario.<ref name=dwight2000/> To the west, the range of endemic blastomycosis extends across southern Manitoba and into adjacent Saskatchewan.<ref name=vallabh1988>{{cite journal|last=Vallabh|first=V|author2=Martin, T |author3=Conly, JM |title=Blastomycosis in Saskatchewan.|journal=The Western journal of medicine|year=1988|volume=148|issue=4|pages=460–2|pmid=3388850}}</ref> A few cases have been reported from north central Alberta, e.g., the Edmonton area, though in these cases an atypical genetic group of the fungus may be involved.<ref name=sekhon1982/>
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| In the rest of the world, ''B. dermatitidis'' occurs at low levels in various parts of Africa, from Algeria to South Africa, as well as in and near the Arabian Peninsula. The African isolates are divided into two biologically different antigen groups: isolates from north of the Sahara are similar to North American isolates in having A and K antigens, while southern African isolates lack the A antigen.<ref name=frean1989/> Isolates from the middle east possess both antigens. The sub-Saharan African isolates differ in the laboratory from other isolates by being exceedingly difficult to convert to the yeast phase, and they also show some enzymatic distinctions.<ref name=summerbell1990/>
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| ==Ecology==
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| ''Blastomyces dermatitidis'' is one of the most ecologically mysterious organisms causing human and animal disease. Prediction of disease risk and prevention of disease are both made extraordinarily difficult by our very poor understanding of where and how this organism normally grows in nature. Despite decades of attempts at isolating organisms from epidemiological foci, ''B. dermatitidis'' has only been isolated from the environment 21 times.<ref name=burgess2006/> Most of these isolations have been based on the arduous isolation techniques involving the suspension of soil or other environmental materials in aqueous medium with antibacterial antibiotics, and injection of mice with these materials, followed by sacrifice of the animals when they appear ill or at the end of six weeks.<ref name=ajello1983/> The internal organs of the mice are then checked microscopically for evidence of blastomycosis. Needless to say, the cost and complexity of performing such studies is imposing, especially as the ethical clearance procedures for work involving animals become ever more involved. More direct and economical mycological techniques for environmental isolation, such as dilution plating, have never yielded positive results for ''Blastomyces'' growth. Since ''B. dermatitidis'' will grow readily from clinical samples on common laboratory media, the lack of success in isolating it from environmental materials is generally ascribed to the inhibitory effects of co-occurring common molds and antibiotic-resistant bacteria.
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| In just one experiment, a single positive ''B. dermatitidis'' culture was gained via use of a novel enrichment broth technique.<ref name=baumgardner1999/> Recently, in an important breakthrough, a specific [[PCR]] technique was developed that was able to detect ''B. dermatitidis'' in three environmental samples from a dog kennel that had been experiencing problems with blastomycosis.<ref name=burgess2006/>
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| What has been learned from direct isolation and recent PCR studies is that ''B. dermatitidis'' tends to be associated with soils and wood debris in areas “characterized by an acidic pH, high organic content (due to rotting or decayed wood or vegetation and animal or bird droppings), abundant moisture, and proximity to waterways”.<ref name=baumgardner1992/> Recent PCR detections, for example, concerned a Kentucky dog kennel where 35 of 100 dogs had contracted blastomycosis.<ref name=burgess2006/> Previous isolations have been from comparable sites such as soil and wood debris from an abandoned Wisconsin [[beaver dam]],<ref name=klein1986/> and woody materials from a Wisconsin woodpile.<ref name=baumgardner1999/> Isolation of ''B. dermatitidis'' was also accomplished from an earthen floor indoors on one occasion.<ref name=bakerspigel1986/>
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| There has been a long history of justifiable speculation that ''B. dermatitidis'' may associate in nature with one or more indigenous North American mammalian host species. To date, however, all the animal species that have been subjected to focused investigation have been exonerated of this specific connection. Unsubstantiated suspicion has particularly focused on the beaver,<ref name=klein1986/><ref name=bradsher1987/><ref name=gaus1996/> but the shrew,<ref name=baumgardner2005/> the bat<ref name=chaturvedi1986/> and the [[prairie dog]]<ref name=degroote2000/> have also been focal points of interest, with no conclusive interspecies association being demonstrated to date. Interestingly, the closely related pathogenic fungus ''P. brasiliensis'' in South America has a well substantiated, though not well understood, ecological link with the nine-banded armadillo, ''[[Dasypus novemcinctus]]''.<ref name=vergara1999/> This member of the mammalian order [[Edentata]] has no close relatives in the geographic range of ''B. dermatitidis''.
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| ==Preventive measures==
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| Avoidance of exposure in endemic areas is the principal means of disease prevention. Because the agent is known to distribute in dusts, the minimization of dust-generating activities, such as digging, sweeping, etc., is key. Although a method of soil decontamination has been described and demonstrated to be effective, it uses hazardous chemicals and its use is best reserved for situations that cannot be managed otherwise.<ref name=ajello1983/>
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| == References ==
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| == References ==
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| {{reflist|30em|refs=
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| <ref name=ajello1983>Ajello, L., and R. J. Weeks. 1983. Soil decontamination and other control measures. Pp. 229-238. In A. F. DiSalvo (ed.), Occupational Mycoses. Lea and Febiger, Philadelphia, Pennsylvania.</ref>
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| <ref name=bakerspigel1986>{{cite journal|last=Bakerspigel|first=A|author2=Kane, J |author3=Schaus, D |title=Isolation of Blastomyces dermatitidis from an earthen floor in southwestern Ontario, Canada.|journal=Journal of clinical microbiology|year=1986|volume=24|issue=5|pages=890–1|pmid=3771778}}</ref>
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| <ref name=baumgardner1992>{{cite journal|last=Baumgardner|first=DJ|author2=Buggy, BP |author3=Mattson, BJ |author4=Burdick, JS |author5= Ludwig, D |title=Epidemiology of blastomycosis in a region of high endemicity in north central Wisconsin.|journal=Clinical infectious diseases : an official publication of the Infectious Diseases Society of America|year=1992|volume=15|issue=4|pages=629–35|pmid=1420675|doi=10.1093/clind/15.4.629}}</ref>
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| <ref name=baumgardner1999>{{cite journal|last=Baumgardner|first=DJ|author2=Paretsky, DP|title=The in vitro isolation of Blastomyces dermatitidis from a woodpile in north central Wisconsin, USA.|journal=Medical mycology : official publication of the International Society for Human and Animal Mycology|year=1999|volume=37|issue=3|pages=163–8|pmid=10421847}}</ref>
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| <ref name=baumgardner2005>{{cite journal|last=Baumgardner|first=DJ|author2=Summerbell, R |author3=Krajden, S |author4=Alexopoulou, I |author5=Agrawal, B |author6=Bergeson, M |author7=Fuksa, M |author8=Bemis, C |author9= Baumgardner, MA |title=Attempted isolation of Blastomyces dermatitidis from native shrews in northern Wisconsin, USA.|journal=Medical mycology : official publication of the International Society for Human and Animal Mycology|year=2005|volume=43|issue=5|pages=413–6|pmid=16178369|doi=10.1080/13693780400008191}}</ref>
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| <ref name=bradsher1987>{{cite journal|last=Bradsher|first=RW|title=Water and blastomycosis: don't blame beaver.|journal=The American review of respiratory disease|year=1987|volume=136|issue=6|pages=1324–6|pmid=3688633|doi=10.1164/ajrccm/136.6.1324}}</ref>
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| <ref name=brown2013>{{cite journal|last=Brown|first=Elizabeth M.|author2=McTaggart, Lisa R. |author3=Zhang, Sean X. |author4=Low, Donald E. |author5=Stevens, David A. |author6=Richardson, Susan E. |author7= Litvintseva, Anastasia P. |title=Phylogenetic Analysis Reveals a Cryptic Species Blastomyces gilchristii, sp. nov. within the Human Pathogenic Fungus Blastomyces dermatitidis|journal=PLoS ONE|date=22 March 2013|volume=8|issue=3|pages=e59237|doi=10.1371/journal.pone.0059237|pmid=23533607|bibcode=2013PLoSO...859237B}}</ref>
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| <ref name=burgess2006>{{cite journal|last=Burgess|first=JW|author2=Schwan, WR |author3=Volk, TJ |title=PCR-based detection of DNA from the human pathogen Blastomyces dermatitidis from natural soil samples.|journal=Medical mycology : official publication of the International Society for Human and Animal Mycology|year=2006|volume=44|issue=8|pages=741–8|pmid=17127631|doi=10.1080/13693780600954749}}</ref>
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| <ref name=chaturvedi1986>{{cite journal|last=Chaturvedi|first=VP|author2=Randhawa, HS |author3=Kini, S |author4= Khan, ZU |title=Survival of Blastomyces dermatitidis in the gastrointestinal tract of an orally infected insectivorous bat, Rhinopoma hardwickei hardwickei Gray.|journal=Journal of medical and veterinary mycology : bi-monthly publication of the International Society for Human and Animal Mycology|year=1986|volume=24|issue=4|pages=349–52|pmid=3746588|doi=10.1080/02681218680000521}}</ref>
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| <ref name=degroote2000>{{cite journal|last=De Groote|first=MA|author2=Bjerke, R |author3=Smith, H |author4= Rhodes III, LV |title=Expanding epidemiology of blastomycosis: clinical features and investigation of 2 cases in Colorado.|journal=Clinical infectious diseases : an official publication of the Infectious Diseases Society of America|year=2000|volume=30|issue=3|pages=582–4|pmid=10722448|doi=10.1086/313717}}</ref>
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| <ref name=dwight2000>{{cite journal|last=Dwight|first=P.J.|author2=Naus, M |author3=Sarsfield, P |author4= Limerick, B |title=An outbreak of human blastomycosis: the epidemiology of blastomycosis in the Kenora catchment region of Ontario, Canada.|journal=Canada communicable disease report = Releve des maladies transmissibles au Canada|year=2000|volume=26|issue=10|pages=82–91|pmid=10893821}}</ref>
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| <ref name=frean1989>{{cite journal|last=Frean|first=JA|author2=Carman, WF |author3=Crewe-Brown, HH |author4=Culligan, GA |author5= Young, CN |title=Blastomyces dermatitidis infections in the RSA.|journal=South African medical journal = Suid-Afrikaanse tydskrif vir geneeskunde|year=1989|volume=76|issue=1|pages=13–6|pmid=2662433}}</ref>
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| <ref name=gaus1996>{{cite journal|last=Gaus|first=DP|author2=Baumgardner, DJ |author3=Paretsky, D |title=Attempted isolation of Blastomyces dermatitidis from rectal cultures of beaver (Castor canadensis) from north central Wisconsin.|journal=Wilderness & environmental medicine|year=1996|volume=7|issue=2|pages=192|pmid=11990111|doi=10.1580/1080-6032(1996)007[0192:ltte]2.3.co;2}}</ref>
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| <ref name=kane1983>{{cite journal|last=Kane|first=J|author2=Righter, J |author3=Krajden, S |author4= Lester, RS |title=Blastomycosis: a new endemic focus in Canada.|journal=Canadian Medical Association journal|year=1983|volume=129|issue=7|pages=728–31|pmid=6616383}}</ref>
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| <ref name=klein1986>{{cite journal|last=Klein|first=Bruce S.|author2=Vergeront, James M. |author3=Weeks, Robert J. |author4=Kumar, U. Nanda |author5=Mathai, George |author6=Varkey, Basil |author7=Kaufman, Leo |author8=Bradsher, Robert W. |author9=Stoebig, James F. |author10= Davis, Jeffrey P. |title=Isolation of Blastomyces dermatitidis in Soil Associated with a Large Outbreak of Blastomycosis in Wisconsin|journal=New England Journal of Medicine|year=1986|volume=314|issue=9|pages=529–534|doi=10.1056/NEJM198602273140901|pmid=3945290}}</ref>
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| <ref name=kwonchung1992>{{cite book|last=Kwon-Chung|first=K.J., Bennett, J.E.|title=Medical mycology|year=1992|publisher=Lea & Febiger|location=Philadelphia|isbn=978-0812114638|author2=Bennett, John E.}}</ref>
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| <ref name=lester2000>{{cite journal|last=Lester|first=RS|author2=DeKoven, JG |author3=Kane, J |author4=Simor, AE |author5=Krajden, S |author6= Summerbell, RC |title=Novel cases of blastomycosis acquired in Toronto, Ontario.|journal=CMAJ : Canadian Medical Association journal = journal de l'Association medicale canadienne|year=2000|volume=163|issue=10|pages=1309–12|pmid=11107469}}</ref>
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| <ref name=lippman2001>{{cite book|last=Lippman|first=M|title=Size-selective health hazard sampling. Pp. . In BS Cohen, CS McCammon (eds.), Air Sampling Instruments, 9th edition. ACGIH Press, Cincinnati, Ohio.|year=2001|publisher=in BS Cohen, CS McCammon (eds.), Air Sampling Instruments, 9th edition. ACGIH Press|location=Cincinnati, Ohio|pages=93–134}}</ref>
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| <ref name=peterson1998>{{cite journal|last1=Peterson|first1=SW|last2=Sigler|first2=L|title=Molecular genetic variation in Emmonsia crescens and Emmonsia parva, etiologic agents of adiaspiromycosis, and their phylogenetic relationship to Blastomyces dermatitidis (Ajellomyces dermatitidis) and other systemic fungal pathogens.|journal=Journal of clinical microbiology|date=October 1998|volume=36|issue=10|pages=2918-25|pmid=9738044}}</ref>
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| <ref name=sekhon1982>{{cite journal|last=Sekhon|first=AS|author2=Jackson, FL |author3=Jacobs, HJ |title=Blastomycosis: report of the first case from Alberta Canada.|journal=Mycopathologia|year=1982|volume=79|issue=2|pages=65–9|pmid=6813742|doi=10.1007/bf00468081}}</ref>
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| <ref name=vergara1999>{{cite journal|last=Vergara|first=ML|author2=Martinez, R|title=Role of the armadillo Dasypus novemcinctus in the epidemiology of paracoccidioidomycosis.|journal=Mycopathologia|year=1999|volume=144|issue=3|pages=131–3|pmid=10531678|doi=10.1023/A:1007034215003}}</ref>
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| <ref name=summerbell1990>{{cite journal|last=Summerbell|first=RC|author2=Kane, J |author3=Pincus, DH |title=Enzymatic activity profiling as a potential biotyping method for Ajellomyces dermatitidis.|journal=Journal of clinical microbiology|year=1990|volume=28|issue=5|pages=1054–6|pmid=2351722}}</ref>
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| <ref name=untereiner2004>{{cite journal |doi=10.2307/3762114 |last1=Untereiner | first1 = Wendy A.|last2=Scott | first2=James A. | last3=Naveau |first3=F.|last4=Sigler |first4=Lynne|last5=Bachewich |first5=J. |last6=Angus |first6=A. |year=2004 |title=The Ajellomycetaceae, a new family of vertebrate-associated Onygenales |journal=Mycologia |volume=96 |issue=4 |pages=812–21 |url=http://www.mycologia.org/cgi/content/full/96/4/812 |accessdate=2010-01-04 |jstor=3762114 |pmid=21148901}}</ref>
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| ==External links==
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| * {{MeshName|Blastomyces}}
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| * http://www.mycology.adelaide.edu.au/Fungal_Descriptions/Dimorphic_Pathogens/Blastomyces/
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| * http://pathmicro.med.sc.edu/mycology/mycology-6.htm
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| [[Category:Ascomycota]]
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