Dimorphic systemic mycoses are caused by fungal pathogens that can change morphology to overcome host defenses. The diseases are geographically restricted and commonly involve inhalation of spores leading to pulmonary infection. Histopathological examination is important for identifying potential pathogens by revealing characteristic tissue morphologies like spherules in coccidioidomycosis or broad-budding yeasts in blastomycosis. Laboratory diagnosis involves microscopy, culture and serology of clinical specimens but cultures require special handling due to their pathogenicity.

1. Dimorphic Systemic Mycoses
By Habtamu Biazin (Asst. Prof of Medical Microbiology)

2. Dimorphic Systemic Mycoses
• Caused by fungal pathogens which can overcome the physiological and cellular
defenses of the normal human host by changing their morphological form.
• They are geographically restricted and
• The primary site of infection is usually pulmonary, following the inhalation of
conidia.
• Histopathology is especially useful and is one of the most important ways of
alerting the laboratory that they may be dealing with a potential pathogen.

3. Dimorphic Systemic Mycoses
Disease Causative organisms Incidence
Blastomycosis Blastomyces dermatitidis Rare*
Coccidioidomycosis Coccidioides immitis/posadasii Rare*
Histoplasmosis Histoplasma capsulatum Rare*
Paracoccidioidomycosis Paracoccidioides brasiliensis/lutzii Rare*
Talaromyces marneffei infection Talaromyces marneffei Rare*
*more common in endemic areas

4. Tissue morphology of dimorphic pathogens
Mycoses Tissue morphology
Blastomycosis Large broad base unipolar budding yeast cells (8-10um).
Coccidioidomycosis Spherules (10-80um) with endospores (2-5um).
Histoplasmosis Small narrow base budding yeast cells (1-5um; 5-2um in var. duboisii)
Paracoccidioidomycosis Large narrow base, multi-budding yeast cells (20-60um).
Talaromyces marneffei Small, oval to ellipsoidal yeast-like cells (3 µm in diameter).
Sporotrichosis Small narrow base budding yeast cells (2-5um).
ARNING: Cultures of Blastomyces dermatitidis, Coccidioides immitis, Histoplasma capsulatum and Talaromyces
marneffei represent a severe biohazard to laboratory personnel and must be handled with extreme caution in an
appropriate pathogen handling cabinet.

5. Morphology of dimorphic pathogens
• In the microscopic morphology, conversion from the mold form to the yeast or
spherule form, and animal pathogenicity have all been used;
• Culture identification by either exoantigen test or DNA sequencing is now
preferred to minimize exposure to the infectious propagules.

6. Blastomycosis
• Blastomycosis is a chronic granulomatous and suppurative disease
• having a primary pulmonary stage
• followed by dissemination to other body sites, chiefly the skin and bone
• The disease was long thought to be restricted to the North American continent
• In recent years autochthonous cases have been diagnosed in Africa, Asia and Europe.
• All available clinical and epidemiological evidence indicates that humans and lower
animals contract blastomycosis from some source in nature.
• However, the natural habitat of B. dermatitidis has yet to be clearly delineated,
despite some reports of its isolation from soil.

7. Clinical manifestations:
• Pulmonary blastomycosis:
• In most individuals pulmonary lesions are asymptomatic and
• are not detected until the infection has spread to other organs.
• Others develop symptoms after an IP of 3-15 weeks.
• In most cases blastomycosis patients present with chronic symptoms such as cough, fever, malaise and weight loss.
• The lesions become more extensive, with continued suppuration and eventual necrosis and cavitation.
• Occasional patients present with an acute onset of infection, with development of high fever, chills, productive cough,
myalgia, arthralgia and pleuritic chest pain.
• Often these patient appear to recover after 2-12 weeks of symptoms
• Some will return months later with lesions at other sites.
• Other patients with acute onset will fail to recover and will develop a chronic chest infection or disseminated infection.
• Chest radiographic findings are variable and are not diagnostic

8. Clinical manifestation…
• Cutaneous blastomycosis:
• Haematogenous spread gives rise to cutaneous lesions in over 70% of patients.
• These tend to be painless and present either as raised verrucous lesions with
irregular borders, or as ulcers.
• The face, upper limbs, neck and scalp are the most frequent sites involved.

9. Cutaneous blastomycosis
Ulcerated granuloma cutaneous blastomycosis

10. Clinical manifestation…
• Osteoarticular blastomycosis:
• Occurs in about 30% of patients with the spine, pelvis, cranial bones, ribs and long bones most
commonly involved.
• Patients often remain asymptomatic until the infection spreads into contiguous joints, or into
adjacent soft tissue causing subcutaneous abscesses.
• Radiological findings are often non-specific and arthritis occurs in up to 10% of patients

11. Clinical manifestation…
• Other forms include
• Genitourinary blastomycosis involving the prostrate, epididymis or testis;
• Haematogenous spread to the brain causing meningitis, and spinal or brain abscess.
• Other organs may also be involved and choroiditis and endophthalmitis have been reported.
• AIDS patient have developed fulminant blastomycosis with widespread dissemination
following endogenous reactivation of previous infection

12. Laboratory diagnosis:
• Clinical material:
• Skin scrapings, sputum and bronchial washings, cerebrospinal fluid, pleural fluid and
blood, bone marrow, urine and tissue biopsies from various visceral organs.
• Direct microscopy:
a) Skin scrapings should be examined using 10% KOH and Parker ink or calcofluor
white mounts;
b) Exudates and body fluids should be centrifuged and the sediment examined using
either 10% KOH and Parker ink or calcofluor white mounts,
c) Tissue sections should be stained using PAS digest, Grocott's methenamine silver
(GMS) or Gram stain.

13. Laboratory diagnosis:….
• Interpretation:
• As a rule, a positive direct microscopy demonstrating characteristic yeast-like
cells from any specimen should be considered significant.
• Note: Tissue sections need to be stained by Grocott's methenamine silver
method to clearly see the yeast-like cells, which are often difficult to observe
in H&E preparations.

14. Laboratory diagnosis….
Tissue sections showing large, broad-base, unipolar budding yeast-like cells, 8-15 um in diameter.

15. Laboratory diagnosis….
• Culture:
• Clinical specimens should be inoculated onto primary isolation media, like
Sabouraud's dextrose agar and Brain heart infusion agar supplemented with
5% sheep blood.
• Interpretation:
• A positive culture from any of the above specimens should be considered
significant.
• WARNING: Cultures of Blastomyces dermatitidis represent a severe biohazard to laboratory personnel
and must be handled with extreme caution in an appropriate pathogen handling cabinet.

16. Laboratory diagnosis….
• Serology: Serological tests are of limited value in the diagnosis of Blastomycosis.
• Identification:
• In the past microscopic morphology, conversion from the mould form to the yeast form, and
animal pathogenicity have all been used; however however culture identification by either
exoantigen test or DNA sequencing is now preferred to minimize exposure to the infectious
propagules.
• Causative agents: Blastomyces dermatitidis

17. Coccidioidomycosis
• A respiratory infection, resulting from the inhalation of conidia
• Typically resolves rapidly leaving the patient with a strong specific immunity to re-
infection
• In some individuals the disease may progress to
• a chronic pulmonary condition or
• a systemic disease involving the meninges, bones, joints and subcutaneous and
cutaneous tissues

18. Coccidioidomycosis…
• Coccidioides immitis is a soil inhabiting fungus endemic in south-western U.S.A.,
northern Mexico and various centres in South America.
• Several cases have now been diagnosed in Australia, all in patients with a history
of travel to endemic areas.

19. Clinical manifestations:
• 60% of individuals suffer a benign and transient chest infection that does not require medical
attention
• Of the 40% who develop symptoms, most will have an acute febrile "flu-like" illness starting 7-28
days (average 10-16 days) after exposure and most patients will recover completely.
• The main symptoms are fever, pleuritic chest pain, cough, malaise, headache, myalgia, night
sweats and loss of appetite.
• Many patients also develop a mild, diffuse erythematous or maculopapular rash on the trunk and
limbs.

20. Clinical manifestations:
• 5-10% of patients that do develop symptoms are left with pulmonary residual nodule or cavity that
is usually detected several months or years later.
• Another 5% of patients may develop metapulmonary dissemination to the meninges, bones, joints
and subcutaneous and cutaneous tissues, within the first few weeks to months after the onset of
primary infection .

23. Laboratory diagnosis
• Clinical material: Skin scrapings, sputum and bronchial washings, cerebrospinal fluid, pleural fluid
and blood, bone marrow, urine and tissue biopsies from various visceral organs.
• Direct microscopy:
a) Skin scrapings should be examined using 10% KOH and Parker ink or calcofluor white
mounts;
b) Exudates and body fluids should be centrifuged and the sediment examined using either
10% KOH and Parker ink or calcofluor white mounts,
c) Tissue sections should be stained using PAS digest, Grocott's methenamine silver (GMS) or
Gram stain.

24. Laboratory diagnosis…

25. Laboratory diagnosis…

27. Laboratory diagnosis…

28. Laboratory diagnosis…
• Culture: Clinical specimens should be inoculated onto primary isolation media, like Sabouraud's
dextrose agar and Brain heart infusion agar supplemented with 5% sheep blood.
• Interpretation: A positive culture from any of the above specimens should be considered
significant.
• WARNING: Cultures of Coccidioides immitis represent a severe biohazard to laboratory personnel
and must be handled with extreme caution in an appropriate pathogen handling cabinet. .

29. Laboratory diagnosis…

30. Laboratory diagnosis…
• Serology:
• Immunodiffusion and/or complement fixation tests for the detection of antibody have proven
to be useful in the diagnosis of Coccidioidomycosis especially in immunocompetent patients.
However, detection of antibodies in immunosuppressed patients is often difficult, with
between 20-50% of patients testing negative.
• Identification:
• In the past microscopic morphology, conversion from the mould form to the yeast or spherule
form, and animal pathogenicity have all been used; however however culture identification by
either exoantigen test or DNA sequencing is now preferred to minimise exposure to the
infectious propagules.
• Causative agents: Coccidioides immitis

31. Histoplasmosis
• Histoplasmosis is an intracellular mycotic infection of the reticuloendothelial system
caused by the inhalation of conidia from the fungus Histoplasma capsulatum.
• Histoplasmosis has a world wide distribution
• The Mississippi-Ohio River Valley in the U.S.A. is recognized as a major endemic region.
Africa, Australia and parts of East Asia, in particular India and Malaysia are also endemic
regions.
• Environmental isolations of the fungus have been made from soil enriched with excreta
from chicken, starlings and bats.

32. Histoplasmosis…
• Three varieties of Histoplasma capsulatum are recognized, depending on the clinical disease:
 var. capsulatum is the common cause of histoplasmosis;
 var. duboisii is the African type and
 var. farciminosum causes lymphangitis in horses
• Histoplasma isolates may also resemble species of Sepedonium and Chrysosporium.
• Traditionally, positive identification required conversion of the mold form to the yeast phase by
growth at 37C on enriched media,
• However, for laboratory safety, culture identification by either exoantigen test or DNA sequencing
is now preferred.

33. Clinical manifestations:
• Approximately 95% of cases of histoplasmosis are inapparent, subclinical or
benign.
• Five percent of the cases have chronic progressive lung disease, chronic cutaneous
or systemic disease or an acute fulminating fatal systemic disease.
• All stages of this disease may mimic tuberculosis.

34. Clinical manifestations:
Histoplasmosis of the lower gum showing ulcer around base of the teeth.

35. Laboratory diagnosis:
• Clinical material:
• Skin scrapings, sputum and bronchial washings, cerebrospinal fluid, pleural fluid and
blood, bone marrow, urine and tissue biopsies from various visceral organs.
• Direct microscopy:
a) Skin scrapings should be examined using 10% KOH and Parker ink or calcofluor
white mounts;
b) Exudates and body fluids should be centrifuged and the sediment examined using
either 10% KOH and Parker ink or calcofluor white mounts,
c) Tissue sections should be stained using PAS digest, GMS or Gram stain.

36. Laboratory diagnosis…
• Histopathology is especially useful and is one of the most important ways of
alerting the laboratory that they may be dealing with a potential pathogen.
• Interpretation:
• As a rule, a positive direct microscopy demonstrating characteristic yeast-like cells from any
specimen should be considered significant.

37. Laboratory diagnosis….
Tissue morphology of H. capsulatum var. capsulatum (left) showing numerous small narrow base budding yeast cells (1-
5um diam) inside macrophages and H. capsulatum var. duboisii (right) showing larger sized budding yeast cells (5-12 um
in diam).

38. Laboratory diagnosis…
• Culture: Clinical specimens should be inoculated onto primary isolation media,
like Sabouraud's dextrose agar and Brain heart infusion agar supplemented with
5% sheep blood.
• Interpretation: A positive culture from any of the above specimens should be
considered significant.
• WARNING: Cultures of H. capsulatum represent a severe biohazard to laboratory
personnel and must be handled with extreme caution in an appropriate pathogen
handling cabinet.

39. Laboratory diagnosis…
Culture of Histoplasma capsulatum showing growth as a mold at 25C and as a yeast at 37C.

40. Laboratory diagnosis….
• Serology:
• Immunodiffusion and/or complement fixation tests for the detection of
antibody have proven to be useful in the diagnosis of Histoplasmosis,
especially in immunocompetent patients.
• However, detection of antibodies in immunosuppressed patients is often
difficult, with between 20-50% of patients testing negative.

41. Laboratory diagnosis….
• Identification:
• Three varieties of Histoplasma capsulatum are recognized, depending on the clinical disease:
var. capsulatum is the common cause of histoplasmosis;
var. duboisii is the African type and
var. farciminosum causes lymphangitis in horses
• Histoplasma isolates may also resemble species of Sepedonium and Chrysosporium.
• Positive identification required conversion of the mold form to the yeast phase by growth at
37℃ on enriched media
• However, for laboratory safety, culture identification by either exoantigen test or DNA
sequencing is now preferred.

42. Paracoccidioidomycosis (PCM)
• PCM is a chronic granulomatous disease that characteristically produces a primary
pulmonary infection, often inapparent, and then disseminates to form ulcerative
granulomata of the buccal, nasal and occasionally the gastrointestinal mucosa.
• The disease in its inception and development is similar to blastomycosis and
coccidioidomycosis.
• The only etiological agent, Paracoccidioides brasiliensis is geographically
restricted to areas of South and Central America.

43. Clinical manifestations:
• Clinical manifestations vary from subclinical infections that are detected only by
skin-test positivity;
• to chronic unifocal infection where only a single organ is involved;
• to chronic multifocal infection where more than one organ is involved.
• A subacute juvenile infection is also recognized

44. Pulmonary paracoccidioidomycosis:
• Most cases have an indolent onset and patients present with chronic symptoms
such as cough, fever, night sweats, malaise and weight loss.
• Chest x-rays are characteristic but not diagnostic.
• The infection must be distinguished from histoplasmosis and tuberculosis.

45. Mucocutaneous paracoccidioidomycosis:
• The mouth and nose are the most usual mucosal sites of infection.
• Painful ulcerated lesions develop on the gums, tongue, lips or palate and can
progress over weeks or months.
• Perforation of the palate or nasal septum may occur.
• Cutaneous lesions often appear on the face around the mouth and nose, although
patient with severe infection can have widespread lesions.

46. Mucocutaneous paracoccidioidomycosis:
Mucocutaneous paracoccidioidomycosis showing extensive destruction of facial features and an ulcerated
lesion on the pharyngeal mucosa

47. Lymphonodular paracoccidioidomycosis:
• Lymphadenitis is common in younger patients. Cervical and submandibular
chains are the most obvious manifestation and lymph nodes may progress to
form abscesses with draining sinuses.
• Disseminated paracoccidioidomycosis:
• Haematogenous spread of P. brasiliensis can result in widespread disseminated
disease; including lesions of the small or large intestine, hepatic lesions,
adrenal gland destruction, osteomyelitis, arthritis, endophthalmitis and
meningoencephalitis or focal cerebral lesions.

48. Laboratory diagnosis:
• Clinical material:
• Skin scrapings, sputum and bronchial washings, cerebrospinal fluid, pleural fluid and blood, bone marrow, and
tissue biopsies from various visceral organs.
• Direct microscopy:
a) Skin scrapings should be examined using 10% KOH and Parker ink or calcofluor white mounts;
b) Exudates and body fluids should be centrifuged and the sediment examined using either 10% KOH and
Parker ink or calcofluor white mounts,
c) Tissue sections should be stained using PAS digest, Grocott's methenamine silver (GMS) or Gram stain.
• Histopathology is especially useful and is one of the most important ways of alerting the laboratory that they
may be dealing with a potential pathogen.

49. Laboratory diagnosis …
Multiple, narrow base, budding yeast cells (steering wheels) of P. brasiliensis. GMS stained lung section (left) and
phase contrast of cells from a culture (right).
• Interpretation:
• As a rule, a positive direct microscopy
demonstrating the presence of large, 20-60
um, round, narrow base budding yeast cells
with multiple budding "steering wheels"
from any specimen should be considered
significant

50. Laboratory diagnosis…
• Culture:
• Clinical specimens should be inoculated onto primary isolation media, like Sabouraud's
dextrose agar and Brain heart infusion agar supplemented with 5% sheep blood.
• Interpretation:
• A positive culture from any of the above specimens should be considered significant.
• Identification:
• Clinical history, tissue pathology, culture identification with conversion to the yeast phase at
37C are important characters.
• Causative agents: Paracoccidioides brasiliensis

51. Talaromyces marneffei infection
• Talaromyces marneffei exhibits thermal dimorphism by growing in living tissue or in culture at
37℃ as a yeast-like fungus or in culture at temperatures below 30℃ as a mold.
• It has a propensity to cause disease in the normal host, as well as in immunosuppressed patients,
• Significantly , it has now become a major opportunistic pathogen in HIV positive patients in
Indochina.
• Over 300 cases have been reported with the majority of these coming from Chiang Mai in northern
Thailand.

52. Talaromyces marneffei infection
• Other predisposing factors include lymphoproliferative disorders, bronchiectasis and tuberculosis,
autoimmune diseases and corticosteroid therapy.
• To date, all naturally occurring infections have been in residents of, or travellers to, southeast Asia;
especially northern Thailand, Vietnam, Hong Kong, Taiwan and southern China.
• Imported cases of P. marneffei infections have been reported from Australia, France, Italy,
Netherlands, UK and USA.

53. Clinical manifestations:
• In patients with normal immunity, T. marneffei infection may either be disseminated or focal. In the
latter, both clinical and histological appearances may strongly resemble tuberculosis (e.g
suppurative lymphadenopathy).
• In HIV patients, T. marneffei infection is usually disseminated at diagnosis. Commonly the skin,
reticuloendothelial system, lung and gut are infected.
• Fungaemia is present in the majority of cases and other organ systems including kidney, bones,
joints and pericardium may also be involved.

54. Clinical manifestations:
• Patients usually present with non-specific symptoms of fever, anaemia and weight loss.
• Skin lesions are most commonly papules often with a central necrotic umbilication similar in
appearance to those seen in molluscum contagiosum and are usually located on the face, trunk and
extremities.
• In many cases numerous subcutaneous abscesses ulcerate over time.
• It is important to note that the clinical symptoms of disseminated infection by T. marneffei mimic
those seen in AIDS patients with disseminated cryptococcal infection or disseminated
histoplasmosis.

55. Talaromyces marneffei infection …

56. Talaromyces marneffei infection

57. Talaromyces marneffei infection
• Finally, little is known about the ecology, epidemiology or pathogenesis of T. marneffei infection.
• Although bamboo rats are known to be asymptomatic carriers of the fungus, it is unclear whether they are an
important reservoir for human infection or only a sentinel animal that is susceptible to infection from an
environmental source.
• Human infections have been reported following traumatic implantation, enteric spread following the eating of
bamboo rats as "game cuisine" and by inhalation of spores from soil or possibly a specific host plant.
• T. marneffei has been isolated from bamboo rat burrows and the current consensus would favour soil as the
most likely reservoir with transmission to humans via the respiratory route, similar to that seen with other
dimorphic fungi.
• However this remains to be proven and for now the natural habitat of the fungus and an explanation for its
geographic restriction remain unknown.

58. Laboratory diagnosis:
• Clinical material:
• Talaromyces marneffei is the only dimorphic member of the genus Talaromyces and is readily
detected by direct microscopy and culture of infected tissues, especially skin lesions, bone
marrow, blood and lymph nodes.
• Direct microscopy:
• A Giemsa stained touch smear of a skin biopsy or bone marrow aspirate is a rapid and
sensitive diagnostic method that readily demonstrates the presence of typical yeast-like cells
with a central septa, either within histiocytes or scattered through the tissue.
• The yeast-cells are spherical to ellipsoidal, 2 to 6 um in diameter, and divide by fission rather
than budding, a characteristic visible on stained touch smears that distinguishes T. marneffei
from Histoplasma capsulatum.

59. Laboratory diagnosis…
• Tissue sections show small, oval to elliptical yeast-like cells, 3um in diameter,
either packed within histiocytes or scattered through the tissue.
• Occasional, large, elongated sausage shaped cells, up to 8 um long, with
distinctive septa may be present.
• Note: tissue sections need to be stained by GMS method to clearly see the yeast-
like cells, which are often difficult to observe in H&E preparations.

60. Laboratory diagnosis…
A Giemsa stained touch smear (left) and a GMS stained tissue section (right) showing typical septate yeast-like cells
of T. marneffei. In the latter preparation the cells closely resemble those seen in histoplasmosis

61. Laboratory diagnosis…
• Culture: Clinical specimens should be inoculated onto primary isolation media,
like Sabouraud's dextrose agar.
Culture showing a typical yellow-pink colony with distinctive red diffusable
pigment of Talaromyces marneffei.

62. Laboratory diagnosis…
• Serology:
• There are currently no commercially available serological procedures for the
diagnosis of Talaromyces marneffei infection.
• Identification:
• Clinical history, tissue morphology and culture identification.
• Causative agents: Talaromyces marneffei