Blastomyces dermatitidis
Blastomyces dermatitidis | |
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Blastomyces dermatitidis, yeast form | |
Scientific classification | |
Kingdom: | Fungi |
Division: | |
Class: | |
Order: | |
Family: | |
Genus: | |
Species: | B. dermatitidis
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Binomial name | |
Blastomyces dermatitidis Gilchrist & W.R.Stokes (1898)
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Blastomyces dermatitidis is a
Morphology and phylogeny
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. The sexual form of this fungus was formerly known as Ajellomyces dermatitidis.[2]
In 2013, a second species was described in the genus Blastomyces,
Along with two other important human-pathogenic fungi,
In nature, the fungus forms a network of thread-like
Geographic distribution and variants
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, C. posadasii and Talaromyces marneffei.
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.[6] 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,[7] and, most notably, has areas of high endemicity throughout northern Ontario.[8] Remarkably high incidence is noted for some parts of the Kenora area and climatologically similar areas of northwestern Ontario.[9] To the west, the range of endemic blastomycosis extends across southern Manitoba and into adjacent Saskatchewan.[10] 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.[11]
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.[12] 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.[13]
Ecology
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.
In just one experiment, a single positive B. dermatitidis culture was gained via use of a novel enrichment broth technique.[16] 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.[14]
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".[17] Recent PCR detections, for example, concerned a Kentucky dog kennel where 35 of 100 dogs had contracted blastomycosis.[14] Previous isolations have been from comparable sites such as soil and wood debris from an abandoned Wisconsin beaver dam,[18] and woody materials from a Wisconsin woodpile.[16] Isolation of B. dermatitidis was also accomplished from an earthen floor indoors on one occasion.[19]
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,
Preventive measures
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.[15]
References
- ^ a b c DiSalvo, A.F. (1992). Al-Doory, Y.; DiSalvo, A.F. (eds.). Ecology of Blastomyces dermatitidis. Plenum. pp. 43–73.
- ^ Bennett, John E. (2014). "Introduction to Mycoses". In John E. Bennett; Raphael Dolin; Martin J. Blaser (eds.). Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. Elsevier Health Sciences. p. 2874.
- PMID 23533607.
- PMID 21148901.
- ^ a b Lippman, M (2001). Size-selective health hazard sampling. Pp. . In BS Cohen, CS McCammon (eds.), Air Sampling Instruments, 9th edition. ACGIH Press, Cincinnati, Ohio. Cincinnati, Ohio: in BS Cohen, CS McCammon (eds.), Air Sampling Instruments, 9th edition. ACGIH Press. pp. 93–134.
- ISBN 978-0812114638.)
{{cite book}}
: CS1 maint: multiple names: authors list (link - PMID 11107469.
- PMID 6616383.
- PMID 10893821.
- PMID 3388850.
- S2CID 27296444.
- PMID 2662433.
- PMID 2351722.
- ^ PMID 17127631.
- ^ a b 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.
- ^ PMID 10421847.
- PMID 1420675.
- ^ PMID 3945290.
- PMID 3771778.
- PMID 3688633.
- PMID 11990111.
- PMID 16178369.
- PMID 3746588.
- PMID 10722448.
- S2CID 35693829.
External links
- Blastomyces at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
- "Blastomyces dermatitidis". Mycology Online § Dimorphic Fungal Pathogens. University of Adelaide. Archived from the original on 2007-08-17. Retrieved 2007-08-04.
- http://pathmicro.med.sc.edu/mycology/mycology-6.htm