Dimorphic fungi can exist in both a mycelial and yeast-like state. They commonly transition between these states depending on temperature, with the mycelial form growing at 25°C and the yeast-like pathogenic form at 37°C. This document discusses two specific dimorphic fungi, Sporothrix schenckii and Histoplasma capsulatum. It defines their morphology and growth characteristics, epidemiology, pathogenesis, clinical presentations, diagnosis and treatment of the diseases they cause - sporotrichosis and histoplasmosis.

1. DIMORPHIC
FUNGI
Prabin Shah
BScMLT, MSc(Biochemistry)
6/20/2015DIMORPHICFUNGI
1

2. DEFINITION
• Dimorphic fungi are fungi that can reproduce as either a mycelial
or a yeast-like state.
• Generally the mycelial saprotrophic form grows at 25° C, and the
yeast-like pathogenic form at 37° C.
• This dimorphism is important in the identification of mycoses, as it
makes rapid identification of many pathogenic organisms possible.
• Some diseases caused by dimorphic fungi are:
• sporotrichosis
• blastomycosis
• histoplasmosis
• coccidioidomycosis
• paracoccidioidomycosis
• penicillosis
6/20/2015DIMORPHICFUNGI
2

3. 6/20/2015DIMORPHICFUNGI
3

4. Dimorphicfungi and diseasecausedby them
FUNGUS DISEASE TARGET ORGANS
BLASTOMYCES
DERMATITIDIS
North american
blastomycosis
Lung, skin.
PARACOCCIDIOIDES
IMMITIS
South american
blastomycosis
Buccal and nasal mucosa
HISTOPLASMA
CAPSULATUM
Histoplasmosis Respiratory system,
pulmonary disease
SPOROTHRIX SCHENCKII Sporotrichosis Nodules in skin, lymph
nodes
6/20/2015DIMORPHICFUNGI
4

5. CONTENTS
• SPOROTRICHOSIS
• INTRODUCTION
• MYCOLOGY
• EPIDEMIOLOGY
• PATHOGENESIS AND PATHOLOGY
• CLINICAL FEATURES
• LAB DIAGNOSIS
• TREATMENT
6/20/2015DIMORPHICFUNGI
5

6. SPOROTRICHOSIS
• Primarily a chronic mycotic infection of the cutaneous or
subcutaneous tissues and adjacent lymphatics
characterized by nodular lesions which may suppurate
and ulcerate.
• Infections are caused by the traumatic implantation of a
dimorphic saprotrophic fungus Sporothrix schenckii into
the skin, or very rarely, by inhalation into the lungs.
• The infection may also occasionally involve the central
nervous system, lungs or genitourinary tract.
• This disease is also called as Rose Gardener’s disease
6/20/2015DIMORPHICFUNGI
6

7. Mycology
• Causative fungus- Sporothrix schenckii
•Family- Ophiostomataceae
•Order- Ophiostomatales
•Class- Unitunicate Pyrenomycetes
•Phylum- Ascomycota
6/20/2015DIMORPHICFUNGI
7

8. EPIDEMIOLOGY
• S.schenckii is a saprophyte associated with plants and
soil.
• It is isolated from various natural sources and dead
vegetation like wood, bark, leaves etc.
• Predominantly occurs in young population due to
frequent contact with natural sources of infection.
• Males are affected 3 times more than that of females.
6/20/2015DIMORPHICFUNGI
8

9. PATHOGENESIS
• S.schenckii produces 2 extracellular proteinases i.e.
proteinase I and proteinase II.
• The former is serine proteinase , inhibited by chymostatin
whereas the latter is an aspartic proteinase inhibited by
pepstatin.
• They play an important role in fungal invasion and growth.
• The 3 granulomatous patterns are;
i. Sporotrichoid type
ii. Tuberculoid type
iii. Foreign body type.
6/20/2015DIMORPHICFUNGI
9

10. CLINICAL FEATURES
• It causes lymphatic and sub cutaneous infection.
• The disease is broadly classified into 5 clinical types.
1. Lymphocutaneous Sporotrichosis
2. Fixed Cutaneous Sporotrichosis
3. Mucocutaneous Sporotrichosis
4. Disseminated Sporotrichosis
5. Pulmonary Sporotrichosis
6/20/2015DIMORPHICFUNGI
10

11. 1. Lymphocutaneous Sporotrichosis
• Commonest type that follows subcutaneous implantation of
spores in a penetrating wound.
• Incubation period varies from 8-30 days.
• Initial manifestation is appearance of a small, firm, non-
tender, mobile subcutaneous nodule which becomes
violaceous and may ulcerate forming sporotrichotic chancre.
• The disease is characterised by involvement of lymphatics
and development of characteristic linear-nodulo-ulcerative
secondary lesions along lymphatics.
• This type of lesion is called “sporotrichoid”
6/20/2015DIMORPHICFUNGI
11

12. Lymphocutaneoussporotrichosisshowingtypicalelevatedsubcutaneous
nodulesdevelopingalongtheregionallymphaticsoftheforearm
6/20/2015DIMORPHICFUNGI
12

13. 2. Fixed Cutaneous Sporotrichosis
• Cutaneous sporotrichosis where the lesions remain
localised to inoculation site.
• Commonly seen among individuals with higher degree of
immunity because of prior exposure to organism.
• Lesions commonly appear on neck, trunk, or face as
ulcerative, verrucose, papular, acneform, gummatous or
erythematoid.
6/20/2015DIMORPHICFUNGI
13

14. 6/20/2015
14
DIMORPHICFUNGI
Fixed cutaneous verrucous-type sporotrichosis of the wrist and hand

15. 3. Mucocutaneous Sporotrichosis
• Lesions develop in mouth, pharynx, vocal cords or nose.
• Lesions are erythematous, ulcerative and suppurative at
first and later granulomatous, vegetative or
papillomatous.
• Regional lymph nodes become enlarged and firm.
6/20/2015DIMORPHICFUNGI
15

16. 4. Disseminated Sporotrichosis
• Occurs by the hematogenous spread from primary lesion
or from suppurating lymph nodes.
• Dissemination is manifested with the beginning of
subcutaneous nodules and later become papules, pustules,
gummata or confluent areas of folliculitis.
• Mostly seen in AIDS patients.
6/20/2015DIMORPHICFUNGI
16

17. 5. Pulmonary Sporotrichosis
• It occurs without the involvement of cutaneous or
subcutaneous tissue.
• Once the conidia of S.schenckii enter lungs, they may form
nodules, cavities or diffuse reticulonodular infiltrates.
• A single cavitary lesion of upper lobe is the most distinctive
feature.
• The solitary residual fibrocaseous nodule- sporotrichoma is an
infrequent pathogenic manifestation of pulmonary
sporitrichosis.
6/20/2015DIMORPHICFUNGI
17

18. LAB DIAGNOSIS
i. Direct microscopy
ii. Fungal culture
iii. Immunodiagnosis
SPECIMEN COLLECTED:
Pus, exudate, aspirate from
Nodules
Curettage
Swabbing from open lesions
6/20/2015DIMORPHICFUNGI
18

19. DIRECT MICROSCOPY
• KOH wet mount preparation
• Shows small, elongated yeast cells .
cigar-shaped and budding S.
schenckii yeast cells.
Direct examination (10% KOH)
of the pus from a lesion of a
human patient with
sporotrichosis, showing
nonspecific budding yeast
cells
6/20/2015DIMORPHICFUNGI
19

20. • GRAM STAIN
• Shows GP irregularly stained yeast cells which are very few in
number.
• IN TISSUE SECTIONS
• Organism appears as cigar shaped bodies yeast cells in H&E and
PAS
• Asteroid bodies may be seen in direct smear examination and on
histopathological examination with H&E.
• The fungi are surrounded by refractile, eosinophilic halo called
Splendore-Hoeppli phenomenon.
6/20/2015DIMORPHICFUNGI
20

21. Section from a fixed cutaneous lesion on the face of a child with
sporotrichosis showing round Periodic Acid-Schiff (PAS)
positive yeast-like cells, one with an elongated bud. Sporothrix
schenckii is a dimorphic fungus and this is the typical parasitic
or yeast-like form seen in tissue. (Courtesy Professor D.
Weedon, Brisbane, Qld.).
6/20/2015DIMORPHICFUNGI
21

22. FUNGAL CULTURE
• Specimens inoculated on 2 sets of SDA, BHIA with actidione,
BA, CA incubated at 25°C and 37°C.
• Colonies at 25°C are initially moist, off-white to cream colored
which appear within 3-5 days and turn gray, brown, or black
leathery in abt 10-14 days.
6/20/2015DIMORPHICFUNGI
22

23. Microscopic morphology of the saprophytic or
mycelial form of Sporothrix schenckii when grown on
SDA at 25oC. Note clusters of ovoid conidia produced
sympodially on short conidiophores arising at right
angles from the thin septate hyphae.
6/20/2015DIMORPHICFUNGI
23

24. • 2 types of sporulation is seen.
• Spore borne individually on delicate sterigma along
hyphae
• pyriform spores borne in small groups
• Depending upon the pattern of orgin of conidiophore, 2
types of appearance seen;
• Flower like pattern
• Palm tree - like
6/20/2015DIMORPHICFUNGI
24

25. Sporothrix schenckii on Sabouraud's dextrose agar grown at
25oC colonies are moist and glabrous, with a wrinkled and
folded surface. Pigmentation may vary from white to cream to
black
6/20/2015DIMORPHICFUNGI
25

26. Microscopic morphology of the parasitic or yeast form of
Sporothrix schenckii when grown on brain heart infusion
agar containing blood and incubated at 370C. Note
budding yeast cells.
6/20/2015DIMORPHICFUNGI
26

27. TREATMENT
• Saturated Solution of Potassium Iodide(SSKI) is the drug of
choice.
• Oral ketoconazole or itraconazole
• Terbinafine
6/20/2015DIMORPHICFUNGI
27

28. •HISTOPLASMOSIS
• INTRODUCTION
• MYCOLOGY
• EPIDEMIOLOGY
• PATHOGENESIS AND PATHOLOGY
• CLINICAL FEATURES
• LAB DIAGNOSIS
• TREATMENT
6/20/2015DIMORPHICFUNGI
28

29. HISTOPLASMOSIS
• An intracellular mycotic infection of the
reticuloendothelial system caused by the
inhalation of the fungus.
• Approximately 95% of cases of histoplasmosis
are inapparent, subclinical or benign.
• 5% of the cases have chronic progressive lung
disease, chronic cutaneous or systemic disease.
• The infection is also known as Darling’s disease.
6/20/2015DIMORPHICFUNGI
29

30. MYCOLOGY
• Causative organism is Histoplasma capsulatum, a
thermally dimorphic fungus.
• 3 varieties of this dimorphic fungi are;
i. H.c.var.capsulatum
ii. H.c.var.duboisii
iii. H.c.var.farciminosum
6/20/2015DIMORPHICFUNGI
30

31. Mycelial colonies of
H.capsulatum
Culture of Histoplasma capsulatum
on SDA showing a white suede-like
colony-albino type
Culture of Histoplasma capsulatum
on SDA showing a white suede-like
colony-brown type
6/20/2015DIMORPHICFUNGI
31

32. EPIDEMIOLOGY
• Causative agent has been isolated from soil.
• Soil with high nitrogen content ecspecially
related to droppings of chickens and bats.
• Adult men are more affected than women.
• 3 types of histoplasmosis are;
i. Histoplasmosis capsulati
ii. Histoplasmosis duboisii
iii. Histoplasmosis farciminosi
6/20/2015DIMORPHICFUNGI
32

33. HISTOPLASMOSIS CAPSULATI
• Classic histoplasmosis
• Highly infectious mycosis
• PATHOGENESIS
• Infection occurs when microconidia are inhaled
and get converted to yeasts in alveolar
macrophages in the lungs.
• Characterized by localized granulomatous
inflammation and dissemination to
reticuloendothelial system.
6/20/2015DIMORPHICFUNGI
33

34. Clinical Features
• Asymptomatic in 90-95%
• Asymptomatic form is indicated by presence of
positive histoplasmin skin test.
• The clinical types are classified as;
1. Acute Pulmonary Histoplasmosis
2. Chronic Pulmonary Histoplasmosis
3. Cutaneous, Mucocutaneous Histoplasmosis
4. Disseminated Histoplasmosis
6/20/2015DIMORPHICFUNGI
34

35. 1.Acute Pulmonary
Histoplasmosis
• It is an acute influenza like self limited illness.
• Characterized by general malaise with fever,
headache, chills, profuse sweating, sore throat,
dry cough, chest pain, and dyspnoea.
• Calcification of lung seen in the later stage.
6/20/2015DIMORPHICFUNGI
35

36. 2.Chronic Pulmonary
Histoplasmosis
• Mostly found in adults with formation of cavities
in the lung either due to primary lesions or
reactivation of apparently healed old lesion.
• Presented with hemoptysis, weight loss,
ulcerative lesions over the lips, mouth, nose,
larynx and intestine.
• The lesions become calcified as concentric rings
i.e. histoplasmoma
6/20/2015DIMORPHICFUNGI
36

37. 3.Cutaneous & Mucocutaneous
Histoplasmosis
• Skin and mucous membrane lesions.
• There is petechial or ecchymotic purpura
on the abdominal wall or thorax.
6/20/2015DIMORPHICFUNGI
37

38. 4.Disseminated Histoplasmosis
• Manifested as fever, anorexia, weight loss,
anemia, leucopenia, hepatosplenomegaly
and lymphadenopathy.
• Late sequelae of subclinical infection is
called Presumed Ocular Histoplasmosis
Syndrome (POHS) characterized by
distinct features as atrophic histo spots
6/20/2015DIMORPHICFUNGI
38

39. LAB DIAGNOSIS
• Specimens collected are;
1. Sputum
2. Bone marrow
3. Lymph nodes aspirate
4. Peripheral blood film
5. Biopsy of lesions from skin, mucous
membrane.
6/20/2015DIMORPHICFUNGI
39

40. Direct Microscopy
• Direct examination of H.capsulatum is best done with H&E
stain.
Tissue section stained
with haematoxylin
and eosin (H&E)
from a biopsy of the
mouth lesion ,
numerous yeast cells
of Histoplasma
capsulatum seen
6/20/2015DIMORPHICFUNGI
40

41. Tissue section stained by Grocott's methenamine silver
(GMS) from a lung biopsy showing numerous yeast cells
of Histoplasma capsulatum inside macrophages.
6/20/2015DIMORPHICFUNGI
41

42. KOH wet mount
• The size of yeast cells being too small is
invariably missed out.
• Therefore thick and thin smears prepared out of
perpheral blood, bone marrow etc are stained
with calcofluor white, giemsa, or wright stains.
• Fungus appear as small, oval yeast cells, within
PMNC.
6/20/2015DIMORPHICFUNGI
42

43. 6/20/2015DIMORPHICFUNGI
43

44. FUNGAL CULTURE
• Inoculated onto SDA with antibacterial
antibiotics and actidione and is incubated at
25°C and 37°C.
• Another set of culture on BHI agar with same
antimicrobials is also inoculated and incubated
as 25°C.
• Special media: Kelley’s medium
6/20/2015DIMORPHICFUNGI
44

45. SEROLOGICAL TESTS
• Serology for histoplasmosis is a little more
complicated than for other mycoses, but it
provides more information than blastomycosis
serology.
• There are 4 tests:
•Latex agglutination
•Complement Fixation
•Immunodiffusion
•EIA
6/20/2015DIMORPHICFUNGI
45

46. 6/20/2015DIMORPHICFUNGI
46

47. TREATMENT
• The drug of choice (DOC) is Amphotericin B,
with all its side effects.
• Itraconazole and Voriconazole is now also being
used.
6/20/2015DIMORPHICFUNGI
47

48. REFERENCES
• Text book of MEDICAL MYCOLOGY
• Jagdish Chander
• A text book of microbiology
• P.Chakraborty
6/20/2015DIMORPHICFUNGI
48

49. 6/20/2015DIMORPHICFUNGI
49