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DIMORPHIC FUNGI

Prabin ShahBScMLT, MSc(Biochemistry)

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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 2

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Dimorphic fungi and disease caused by 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 4

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CONTENTS

• SPOROTRICHOSIS

• INTRODUCTION•MYCOLOGY• EPIDEMIOLOGY• PATHOGENESIS AND PATHOLOGY• CLINICAL FEATURES• LAB DIAGNOSIS• TREATMENT

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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

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Mycology

•Causative fungus- Sporothrix schenckii

•Family- Ophiostomataceae

•Order- Ophiostomatales

•Class- Unitunicate Pyrenomycetes

•Phylum- Ascomycota7

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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.8

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 typeii. Tuberculoid typeiii. Foreign body type.

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CLINICAL FEATURES• It causes lymphatic and sub cutaneous infection.

• The disease is broadly classified into 5 clinical types.

1. Lymphocutaneous Sporotrichosis2. Fixed Cutaneous Sporotrichosis3. Mucocutaneous Sporotrichosis4. Disseminated Sporotrichosis5. Pulmonary Sporotrichosis

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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”11

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Lymphocutaneous sporotrichosis showing typical elevated subcutaneous nodules developing along the regional lymphatics of the forearm

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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.

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14Fixed cutaneous verrucous-type sporotrichosis of the wrist and hand

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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.

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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.

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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.

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LAB DIAGNOSISi. Direct microscopy

ii. Fungal culture

iii. Immunodiagnosis

SPECIMEN COLLECTED:

Pus, exudate, aspirate from

Nodules

Curettage

Swabbing from open lesions

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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

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• 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.

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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.).

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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.

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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.

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• 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

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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

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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.

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TREATMENT• Saturated Solution of Potassium Iodide(SSKI) is the drug of

choice.

• Oral ketoconazole or itraconazole

• Terbinafine

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•HISTOPLASMOSIS• INTRODUCTION

•MYCOLOGY

• EPIDEMIOLOGY

• PATHOGENESIS AND PATHOLOGY

• CLINICAL FEATURES

• LAB DIAGNOSIS

• TREATMENT 28

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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.29

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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

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Mycelial colonies of H.capsulatumCulture 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

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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 32

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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.

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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 Histoplasmosis34

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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.

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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 36

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3.Cutaneous & Mucocutaneous Histoplasmosis

• Skin and mucous membrane lesions.

• There is petechial or ecchymotic purpura on the abdominal wall or thorax.

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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

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LAB DIAGNOSIS

• Specimens collected are;1. Sputum2. Bone marrow3. Lymph nodes aspirate4. Peripheral blood film5. Biopsy of lesions from skin, mucous

membrane.

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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

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

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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.

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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 medium44

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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

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TREATMENT

• The drug of choice (DOC) is Amphotericin B, with all its side effects.

• Itraconazole and Voriconazole is now also being used.

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REFERENCES

• Text book of MEDICAL MYCOLOGY

• Jagdish Chander

• A text book of microbiology

• P.Chakraborty

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GITHANK YOU

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