Blastomycosis is a fungal infection caused by Blastomyces dermatitidis that can affect the lungs, skin, and bones. It is contracted by inhaling spores found in soil and is characterized by a pulmonary infection that can disseminate throughout the body. Symptoms vary depending on the infected area but may include cough, fever, and skin lesions. Diagnosis involves culturing samples on agar to demonstrate the fungus's dimorphic nature and ability to convert between mold and yeast forms depending on temperature. Treatment involves antifungal medications such as itraconazole.

1. BLASTOMYCOSIS
(Blastomyces dermatitidis)
Sundar Khadka,
Microbiologist
HIV Reference Unit, NPHL

2.  Blastomycosis is a chronic granulomatous and
suppurative disease having a primary pulmonary
stage that is frequently followed by
dissemination to other body sites, chiefly the
skin and bone.
 Although the disease was long thought to be
restricted to the North American continent, in
recent years cases have been diagnosed in
Africa, Asia and Europe.

3.  Casper Gilchrist first reported the disease in
1894 from Baltimore in a patient with lesions
involving the skin.
 Clinical entity designated in his honour as
Gilchrist’s disease
 Chicago disease or North American
Blastomyces
 Thermal basis of dimorphism first described
by Hamburger in 1907
 Dermatitidis- infection of skin

4.  Acidic soils with rich organic debris such as
decaying vegetative matter
 rotting wood
 feces of birds and bats(providing increased
nitrogen content)

5. 5

7.  General characteristics:

 Dimorphic fungi that behaves in two
different manners according to temperature
of environment :

 o Mold-like at 25 C
 § Branched hyphae are present

 o Yeast-like at 37 C
 § Broad-based yeast buds are present

8.  Dimorphic fungi
Macroscopic morphology
 Filamentous fungus form:
 Grown at 25 to 30oC:
 Exhibits a cottony or downy texture(covered with
fine, soft hair or feathers)
 Colonies produce white Arial hyphae on the surface
which may turn a yellowish to tan(pale brown)
colour as the colony ages. The reverse is typically
a light tan to brown.
 Moderately slow growth, usually maturing in about
2 weeks but suspect cultures should be held for 8
weeks

10.  Microscopic Morphology
 Filamentous fungus form
 septate hyphae
 Unbranched conidiophores of rather short, yet
varying length extend from the hyphae
 Conidia are hyaline (clear) and are produced
singly at the apex of the conidiophore or can
develop directly on the hyphae.
 Conidia are unicellular, round to pyriform (tear-
drop) in shape (~2 to 10 µm dia.)
 Conidia at the terminal end of the conidiophore
resemble a ‘lollipop’ in structure.

15.  Yeast form
 Grown at 37oC:
 Slow to moderate growth
 Best chance for conversion :Blood Agar or Brain-Heart
Infusion (BHI)) incubated in about 6% CO2.
 yeast form cream to tan in colour , heaped or wrinkled,
granular to verrucose (like a wart or warts).
 The yeast form of Blastomyces dermatitidis inhibited by
cycloheximide.

16.  Yeast Form
 Grown at 37oC: (enhanced by rich media and CO2, or in
infected tissue)
 Yeast-like cells (~8 to 15 µm dia.) exhibit a broad budding
base (4 to 5 µm dia.)
 broad‐based bud or “dumbbell-shaped” or letter 8
 The budding cell usually remains attached to the parent
cell, separating only when reaching the same size as the
parent.

17.  Yeast cells have thick, refractile walls.
 Older cultures may produce thick-walled
chlamydoconidia (7 to 18 µm dia.)
 Note that this organism forms a broad‐based bud,
whereas Cryptococcus neoformans is a yeast that forms a
narrow‐based bud.

18.  Two types
 AK type: worldwide
 K type: prevalent in Africa and smaller in size

19.  Portal of entry
 primary mycoses – respiratory portal; inhaled spores
 subcutaneous - inoculated skin; trauma
 cutaneous and superficial – contamination of skin
surface
•Humans are susceptible to acquiring infections by
close contact with dogs or through scratches and
bites.

21.  Virulence factors –
 thermal dimorphism
 toxin production
 capsules and adhesion factors
 hydrolytic enzymes
 inflammatory stimulants

22.  Transmission: inhalation of conidia à yeast form once in lungs
 Once inside the lungs, the change of environment (carbon dioxide
content, organic nutrients, pH and primarily the increased
temperature (37oC)), and causes the fungal spores to develop into the
yeast cell form.
 The yeast form is disseminate to other areas of the body via blood
 Symptoms may not appear for up to 120 days post infection.

23.  Inflammatory pyogranulomatous reactions occur at the
initial pulmonary site and at the widespread foci of
infection
 Pyogranulomatous is supparative of neutrophils followed
by granulomas of mononuclear cells.
 Mixed neutrophilic and mononuclear cells response is
distinctive of blastomycosis
 Necrosis and fibrosis may occur
 granuloma donot caseate

24.  Asymptomatic: 50% of infections
 Blastomycosis symptoms often mimic symptoms of upper
respiratory infections
 The incubation period is 30 to 100 days, although infection can
be asymptomatic
 When individuals are exposed to Blastomyces dermatitidis the
early symptoms may include:
 Approximately 25% of diagnosed Blastomycosis cases affect the
lungs.
 While 35% of diagnosed cases involve both the lungs and skin
 dry cough
 fever
 heavy sweating
 fatigue
 general feeling of ill health

25. 1. Pulmonary Blastomycosis
 Acute Pulmonary: lobar or segmental consolidation,
mimics bacterial pneumonia
 Chronic Pulmonary: lobar infiltrates mimics
bronchogenic carcinoma
2. Cutaneous Blastomycosis
Skin: ulcerative lesions, subcutaneous nodules
that abscess
3.Osseous Blastomycosis
osteomyelitis

26. 4. Disseminated Blastomycosis
 Bone / Joint: long bones, ribs, vertebrae
osteolytic
 Genitourinary Tract: prostate and epididymis
 Other organs: CNS, pericardium, adrenal gland,
GI
5. Miscellaneous types of Blastomycosis
 Extension of pulmonary
 Liver and spleen mostly affected
 Granulomatous lesions present

27. Skin lesions resulting from the
dissemination of the fungus from the
lungs

28.  Laboratory specimens depend on the
manifestation of the disease:
 pulmonary infection: sputum, BAL, Tracheal
secretions, transbronchial biopsy
 skin lesions: skin scrapings or pus, biopsy from
skin lesions
 Other specimens : biopsy of granulomatous
lesions, Exudates, urine for antigen detection

29.  Direct Demonstration
 KOH
 HE stain
 PAS stain
 GMS stain
 Broad based budding yeast cells

35.  Media:
1. Sabourauds dextrose agar,
2. BHI agar,
3. Blood agar,
4. Blood – Glucose- cysteine agar
 at 25°C and 37° C
 On Sabourauds dextrose agar25°C to 30° C:
 Initially the colony appears yeast-like at room temperature and then
develops hyphal projections, eventually becoming a fluffy white
mould.
 In microscopic Examination, B. dermatitidis has round to pyriform, 4
to 5 μm conidia attached directly to the hyphae or on short stalks.

36.  1.demonstrating conversion between the
dimorphic forms.(Mold to Yeast Conversion;
M to Y)
 Media: Brain Heart Infusion agar, Blood agar,
Blood-glucose- cysteine agar, Cottonseed agar,
Cysteine heart agar with rabbit blood
 2. identification using DNA probes
 3. testing for a specific exoantigen by
immunodiffusion.

37.  The mold colony inoculated to the surface of blood
agar and incubated for 3 -5 days at 37°C.
 prickly appearance colonies , suggesting an
intermediate stage of conversion.
 lactophenol blue mount of a portion of one of the
prickly colonies illustrates a short hyphal segment
that is converting into spherical yeast forms.
 A few individual yeast forms are also present.
 These yeast forms are relatively large with broad-
based attachments. This is characteristic of the
yeast conversion forms of Blastomyces dermatitidis.

38. • Skin test
• Serological test
• Immunodiffusion test (precipitin)
• Complement fixation (CF) test
• Enzyme Immunoassay (EIA).
Immunodiagnosis

39. • Antigen detection in urine
• Molecular Diagnosis
• DNA probes

40. • Intraperitoneal injection of conidia and
mycelial form produce infections in mice ,
guinea pigs, rats and hamsters
• Yeast form equally effective in causing
extensive lesions and death of mice
Animal Pathogenicity