[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"$fxLN3MUwXCdr5RPjwZYIDpOj8CHyjOmngWTgoKXPtZbg":3,"$fw-oNQgJmuNeshfuHq7XDAptq61wgji-0JN06rPCwx0c":32,"$f3Ft0rKFJHppdzE-vuveecxx1BUcg9iOlMLtyzf_MJDg":82},[4,8,12,16,20,24,28],{"title":5,"slug":6,"path":7},"About Microbeonline.com","about-microbeonline-com","\u002Fabout-microbeonline-com\u002F",{"title":9,"slug":10,"path":11},"About Me","about-me","\u002Fabout-microbeonline-com\u002Fabout-me\u002F",{"title":13,"slug":14,"path":15},"Advertise with Us","advertise-us","\u002Fadvertise-us\u002F",{"title":17,"slug":18,"path":19},"Privacy Policy","privacy-policy","\u002Fprivacy-policy\u002F",{"title":21,"slug":22,"path":23},"Abbreviations","abbreviations","\u002Fabbreviations\u002F",{"title":25,"slug":26,"path":27},"Microbes","microbes","\u002Fmicrobes\u002F",{"title":29,"slug":30,"path":31},"Books","recommended-books","\u002Frecommended-books\u002F",{"type":33,"data":34},"blog",{"slug":35,"title":36,"description":36,"seoTitle":37,"seoDescription":37,"author":38,"createdDate":39,"lastUpdatedDate":40,"draft":41,"category":42,"image":37,"body":43,"faq":44,"tags":45,"related":47},"blastomyces-dermatitidis-pathogenesis-diagnosis","Blastomyces dermatitidis: Pathogenesis, Lab Diagnosis",null,"Acharya Tankeshwar","2019-12-14","2026-07-17",false,"mycology","*Blastomyces dermatitidis* is a thermally [dimorphic fungus](\u002Fnotable-dimorphic-fungi-and-their-properties\u002F) that grows as a mycelial form in the environment and as a thick-walled budding yeast in tissues (at 37°C). It causes blastomycosis, a chronic granulomatous and suppurative disease also called Gilchrist disease or North American blastomycosis.\n\n*B. dermatitidis* grows as a mold in warm, moist wooded terrain rich in decaying wood, leaves or debris. Geographically, it is endemic to North America, including the Ohio and Mississippi River valleys and Canada.  Blastomycosis cases have also been documented in India, Africa, and Central and South America.\n\n![ - Biology of Blastomycosis](https:\u002F\u002Fassets.microbeonline.com\u002Fblogs\u002Fbiology-of-blastomycosis-600px.png)Figure: Biology of Blastomycosis\n\nHuman infection results following the inhalation of airborne conidia when soil containing microfoci of mycelia is disturbed. Men are affected more often than women, with the ratio of men to women ranging from 4 : 1 to 15 : 1.  Although blastomycosis affects immunocompromised individuals, it can affect healthy individuals as well. Infections often develop in people who have contact with soil, work outside, or frequently engage in outdoor activities such as campers, outdoorsmen and hunters.  Some cases of human-human transmission have been noted.\n\n### Pathogenesis\n\nAlveolar macrophages, neutrophils, and monocyte provide natural resistance to infection with conidia of *B. dermatitidis.* Alveolar macrophage also inhibits the transformation of conidia to pathogenic yeast form. Yeast form of *Blastomyces dermatitidis* is very resistant to [phagocytosis](\u002Fphagocytosis-mechanism-and-steps\u002F) and killing as it possesses a thick capsule. The proliferation of yeast forms in the alveoli signals the failure of natural resistance to *B. dermatitidis*.\n\nIf natural defenses in the alveoli fail to contain the infection, lymphohematogenous dissemination ensues. This may lead to the involvement of the skin, bone, genitourinary tract, and central nervous system. With the development of immunity **pyogranulomatous lesions** appear in lungs and other infected sites followed by the formation of noncaseating granulomas.\n\nUnlike [cell-mediated immunity](\u002Fcell-mediated-immunity\u002F) which prevents the progress of blastomycosis, humoral immune responses do not play a significant role in host defense against *B. dermatitidis*.\n\n### Clinical signs and symptoms\n\n*B. dermatitidis* is inhaled into the lungs and causes pneumonitis. Clinically, pulmonary symptoms (cough, sputum production, chest pain, and dyspnea) predominate.  If not treated or if the immunity failed to contain the pathogen, lymphohematogenous spread may lead to involvement of the skin, bone, and genitourinary tract.  The signs and symptoms of which varies according to the site of involvement.\n\n1. Pulmonary blastomycosis\n2. Extrapulmonary blastomycosis\n\nCutaneous (development of verrucous or ulcerative type of skin lesions) Osseous (osteomyelitis along with contagious tissue abscesses and draining sinuses) Genitourinary (Involvement of prostate and epididymis in men) Central nervous system (Brain abscess, cranial or epidural abscess, and meningitis)\n\nThe clinical disease takes two forms, cutaneous and systemic. *B. dermatitidis* is inhaled into the lungs and causes pneumonitis. Clinically, pulmonary symptoms (cough, sputum production, chest pain, and dyspnea) predominate.\n\n### Laboratory diagnosis\n\nLaboratory diagnosis of blastomycosis is based on culture and direct visualization of round, multinucleated yeast forms that produce daughter cells from a**single broad-based bud**.\n\n**Sample**: Sputum, bronchoalveolar lavage, biopsy, CSF, bone marrow or pus from the abscess based on the clinical manifestations.\n\n**Microscopy and staining:** [KOH wet mount](\u002Fkoh-preparation-test-principle-procedure-results-uses\u002F) and hematoxylin & eosin staining are used routinely to check the presence of characteristics yeast cells in the clinical specimens. Presence of **characteristics double-contoured, thick-walled, multinucleated yeast forms with single broad-based budding daughter cells** confirms the diagnosis but a negative result does not exclude the possibility of blastomycosis.\n\n![ - Blastomyces dermatitidisin Lung Fine Needle Aspiration Assay stained with PAS.The insert shows large broad-based budding as a daughter cell is being produced.(Image source:http:\u002F\u002Fthunderhouse4-yuri.blogspot.com\u002F)](https:\u002F\u002Fassets.microbeonline.com\u002Fblogs\u002FBlastomyces-dermatitidis-in-Lung-Fine-Needle-Aspiration-Assay-Stained-with-PAS.jpg)Figure: *Blastomyces dermatitidis* in Lung Fine Needle Aspiration Assay stained with PAS.The insert shows large broad-based budding as a daughter cell is being produced.(Image source:http:\u002F\u002Fthunderhouse4-yuri.blogspot.com\u002F)\n\nSometimes, special staining like Periodic Acid Schiff (PAS) and Gomori Methenamine Silver Stain (GMS) may be required for the identification.\n\n### Culture\n\n![ - Colonies ofBlastomyces dermatitidisin SDA after 7 days of growth  (Image source:http:\u002F\u002Fthunderhouse4-yuri.blogspot.com\u002F)](https:\u002F\u002Fassets.microbeonline.com\u002Fblogs\u002F01-Blastomyces-dermatitidis-SAB-14d.jpg)Figure: Colonies of *Blastomyces dermatitidis* in SDA after 7 days of growth (Image source:http:\u002F\u002Fthunderhouse4-yuri.blogspot.com\u002F)\n\nCurrently, culture is the most sensitive method for the diagnosis of blastomycosis. Specimens are inoculated into general-purpose growth media, such as [Sabouraud dextrose agar](\u002Fsabouraud-dextrose-agar-sda-principle-composition-uses-colony-morphology\u002F), potato dextrose agar, potato flake agar, or inhibitory mold agar and are incubated at 25 to 30°C for 4 to 6 weeks.\n\nIf the specimen is likely to be contaminated with saprophytic fungi and\u002For bacteria, selective media containing cycloheximide and antibacterial should be used. For tissue specimen use of enrichment culture medium such as [brain heart infusion agar](\u002Fbrain-heart-infusion-bhi-broth-composition-preparation-and-uses\u002F) supplemented with blood increases the yield.\n\nGrowth of the *B. dermatitidis* will be apparent on [fungal isolation media](\u002Fcommon-fungal-culture-media-uses\u002F) within 10-30 days. Initially, colonies are white to off-white and glabrous or waxy in appearance, which becomes gray to brown as aerial hyphae develop with age.\n\n![ - “lollipop-like” conidiophore-conidia structures ofB. dermatitidis(Image source:http:\u002F\u002Fthunderhouse4-yuri.blogspot.com\u002F)](https:\u002F\u002Fassets.microbeonline.com\u002Fblogs\u002F06-Blastomyces-dermatitidis-400X.jpg)Figure: “lollipop-like” conidiophore-conidia structures of *B. dermatitidis* (Image source:http:\u002F\u002Fthunderhouse4-yuri.blogspot.com\u002F)\n\n**Microscopic feature (of mold form):**\n\n- Delicate septate hyphae measuring 1 to 2 μm in diameter\n- **Oval or pyriform single-celled conidia** measuring 2 to 4 μm in diameter,\n- Conidia are found singly at the tips of short or long conidiophores and **resemble lollipops**\n\n![ - Slightly pyriform (tear-drop) shaped conidia  ofB. dermatitidis(Image source:http:\u002F\u002Fthunderhouse4-yuri.blogspot.com\u002F)](https:\u002F\u002Fassets.microbeonline.com\u002Fblogs\u002FBlastomyces-dermatitidis-Conidia.jpg)Figure: Slightly pyriform (tear-drop) shaped conidia  of *B. dermatitidis* (Image source:http:\u002F\u002Fthunderhouse4-yuri.blogspot.com\u002F)\n\nOnce sufficient growth of fungi is noted **chemiluminescent DNA probe** can be used to confirm the isolate as *B. dermatitidis*. Other ways to confirm an identification of *B. dermatitidis* are checking conversion of the mold to the yeast form (which is very time consuming), repetitive-sequence-based PCR and nucleic acid sequencing.\n\n### Antigen Detection\n\nTests for the detection of *B. dermatitidis* antigen in urine is available in some reference laboratories. It showed more than 90% sensitivity but specificity is too low. People suffering from histoplasmosis, paracoccidioidomycosis and penicilliosis also give positive results.\n\n### Antibody detection tests\n\nTests for the detection of antibodies to *B. dermatitidis* are available commercially but not adequate for the diagnosis of blastomycosis.\n\n- **Complement fixation test** using yeast-phase antigen: Sensitivity and specificity are too low.\n- **Immunodiffusion** using purified *B. dermatitidis A* antigen: Better than complement fixation test. Sensitivity is around 65-80%.\n- **Enzyme immunoassays**: More sensitive than immunodiffusion but less specific\n\n### Nucleic Acid Amplification\n\nNucleic acid amplification tests for direct detection of *B. dermatitidis* in clinical specimens are not in routine use.\n\n#### Treatment\n\nAmphotericin is the treatment of choice. Initial treatment usually requires an amphotericin preparation administered intravenously, followed by oral itraconazole.\n\n**Special acknowledgement**\n\nI am grateful to yuri for the beautiful photographs of *B.dermatitidis*. For more images please visit \u003Chttp:\u002F\u002Fthunderhouse4-yuri.blogspot.com\u002F2012\u002F12\u002Fblastomyces-dermatitidis.html>\n\n#### References and further readings\n\n1. Saccente M, Woods GL. 2010. [Clinical and laboratory update on blastomycosis](https:\u002F\u002Fcmr.asm.org\u002Fcontent\u002F23\u002F2\u002F367). Clin Microbiol Rev 23:367–381. doi:10.1128\u002FCMR.00056-09\n2. [Blastomycosis.](https:\u002F\u002Fwww.cdc.gov\u002Ffungal\u002Fdiseases\u002Fblastomycosis\u002Findex.html) Center for Disease Control and Prevention.",[],[46],"dimorphic-fungi",[48,54,60],{"slug":49,"title":50,"description":50,"seoTitle":37,"seoDescription":37,"author":38,"createdDate":51,"lastUpdatedDate":40,"draft":41,"category":42,"image":37,"faq":52,"tags":53},"histoplasma-capsulatum-properties-diseases-laboratory-diagnosis","Histoplasma capsulatum: Properties, Diseases, Lab Diagnosis","2016-06-24",[],[46],{"slug":55,"title":56,"description":56,"seoTitle":37,"seoDescription":37,"author":38,"createdDate":57,"lastUpdatedDate":40,"draft":41,"category":42,"image":37,"faq":58,"tags":59},"overview-of-sporotrichosis-rose-gardeners-disease-and-laboratory-diagnosis","Sporothrix: Characteristics, Pathogenesis and Lab Diagnosis","2013-08-01",[],[46],{"slug":61,"title":62,"description":63,"seoTitle":37,"seoDescription":37,"author":38,"createdDate":64,"lastUpdatedDate":40,"draft":41,"category":42,"image":37,"faq":65,"tags":81},"notable-dimorphic-fungi-and-their-properties","Dimorphic Fungi: Disease, Properties","Dimorphic fungi — Histoplasma, Blastomyces, Coccidioides, Paracoccidioides, Sporothrix, Talaromyces. Mold-to-yeast conversion, mnemonics, geographic distribution, and clinical findings. Complete teaching guide.","2013-05-29",[66,69,72,75,78],{"question":67,"answer":68},"Why do dimorphic fungi change shape based on temperature?","Thermal dimorphism is a virulence adaptation. Mold form (25-30°C) optimises environmental spore dispersal. Yeast form (35-37°C, body temp) is smaller, survives within macrophages, and resists immune clearance better — a deliberate survival strategy, not incidental.",{"question":70,"answer":71},"Why must dimorphic fungal cultures be handled in a biosafety cabinet?","The mold form's airborne conidia are the infectious form for humans. Examining cultures on an open bench risks aerosolising conidia, causing laboratory-acquired infection — a well-documented occupational hazard requiring BSL containment for suspected dimorphic cultures.",{"question":73,"answer":74},"Which dimorphic fungi do NOT follow the typical mold-to-yeast pattern?","Coccidioides immitis forms a spherule (20-200 μm, filled with endospores) instead of a true yeast. Talaromyces marneffei divides by fission (central septum) rather than budding. Both are common exam traps precisely because they break the general pattern.",{"question":76,"answer":77},"Why is geographic\u002Ftravel history important when dimorphic fungal infection is suspected?","Each organism has highly specific environmental niches: Histoplasma (Ohio\u002FMississippi valleys, bird\u002Fbat droppings), Coccidioides (SW USA arid soil), Blastomyces (Great Lakes\u002FOhio region), Paracoccidioides (rural Latin America), Talaromyces (Southeast Asia). Travel\u002Foccupational history dramatically narrows the differential before any test.",{"question":79,"answer":80},"Is Sporothrix schenckii a systemic or subcutaneous pathogen?","Primarily subcutaneous (sporotrichosis) — unique among classic dimorphic fungi. Acquired by traumatic inoculation (rose thorns, splinters — 'rose gardener's disease'), typically remains localized with lymphocutaneous spread. Systemic dissemination is rare, occurring almost exclusively in severe immunocompromise.",[46],[83,89,96,101,105,109,114,119,123,127],{"slug":84,"name":38,"description":85,"image":86,"body":87,"postCount":88},"acharya-tankeshwar","Editor-in-chief","https:\u002F\u002Fassets.microbeonline.com\u002Fauthors\u002Ftankeshwar-acharya-author-microbeonline.jpg","***Tankeshwar Acharya, MSc (Medical Microbiology)***\n\n*Tankeshwar Acharya is an Assistant Professor in the Department of Microbiology at Patan Academy of Health Sciences (PAHS), Nepal, where he has been teaching and practicing clinical microbiology for over 14 years. He is the founder of Microbe Online, one of the leading free microbiology education resources on the web, covering bacteriology, mycology, parasitology, immunology, and clinical laboratory diagnostics written from direct experience in both the classroom and the diagnostic laboratory.*",432,{"slug":90,"name":91,"description":92,"image":93,"body":94,"postCount":95},"ashma-shrestha","Ashma Shrestha","SEO Copywriter and Science Communicator\nKathmandu, Nepal","https:\u002F\u002Fassets.microbeonline.com\u002Fauthors\u002Fashma-shrestha.png","Ashma Shrestha holds a Master of Science in Medical Microbiology from the Institute of Science and Technology (IOST), Tribhuvan University, Nepal, where she developed a strong foundation in virology, molecular biology, and diagnostic microbiology.\n\nShe now works as an SEO Copywriter at Resolution Digital, where she combines her scientific training with research-driven content strategy. She is certified in Google Analytics and Google Business Profile (GBP), and brings a data-informed approach to science communication writing content that is not only accurate but structured to reach and serve the students who need it most.\n\nAt microbeonline, Ashma contributes articles primarily in virology and molecular biology, areas she finds most compelling for their mechanistic depth and their growing clinical relevance. Her writing reflects the same standard the site is built on: factual rigor, clear explanation of the *why* behind microbiology concepts, and content that helps students move from memorization to genuine understanding.\n\nShe is passionate about making complex microbiological concepts accessible without sacrificing accuracy; a skill that sits at the intersection of her scientific training and her professional work in content and SEO.",81,{"slug":97,"name":98,"description":99,"image":37,"body":37,"postCount":100},"sushmita-baniya","Sushmita Baniya","Author \u002F Contributor",32,{"slug":102,"name":103,"description":99,"image":37,"body":37,"postCount":104},"samikshya-acharya","Samikshya Acharya",20,{"slug":106,"name":107,"description":99,"image":37,"body":37,"postCount":108},"alisha-tripathi","Alisha Tripathi",6,{"slug":110,"name":111,"description":112,"image":37,"body":37,"postCount":113},"aastha-shrestha","Aastha Shrestha"," Author \u002F Contributor",10,{"slug":115,"name":116,"description":117,"image":37,"body":37,"postCount":118},"guest-author","Guest Author","Guest Author \u002F Contributor",2,{"slug":120,"name":121,"description":99,"image":37,"body":37,"postCount":122},"srijana-khanal","Srijana Khanal",18,{"slug":124,"name":125,"description":117,"image":37,"body":37,"postCount":126},"dr-poonam-acharya","Dr. Poonam Acharya",1,{"slug":128,"name":129,"description":99,"image":37,"body":130,"postCount":131},"nisha-rijal","Nisha Rijal","**Nisha Rijal** is a microbiologist and quality assurance specialist. She served for nearly 12 years as a microbiologist at the National Public Health Laboratory (NPHL), Nepal's national reference laboratory, and continues to work as a consultant microbiologist in international public health organization. ",51]