Systemic Mycoses

Caustive agents Histoplasma capsulatumBlastomyces dermatitidis Cryptococcus neoformansCoccidioides immitisParacoccidioides brasillensis

HistoplasmosisCausative Agent Histoplasma capsulatum var capsulatumHistoplasma capsulatum var. duboisii o The organism is misnamed because:

It infects macrophages NOT plasma cells & It is non-capsulated

Morphology Dimorphic fungus Smallest yeast cells Reproduce by budding

Source of Infection• Soil containing bird or bat excreta• No case to case transmissionPathogenesis• Spores are inhaled, engulfed by

macrophages and develop into yeast forms

• Granulomas formed in the lung which may get calcified like TB

• Disseminate and may infect macrophages in RES (liver, spleen, LN & BM)

Histoplasmosis

Histoplasma yeasts within macrophages

Clinical Features

• In immunocompetent personso Asymptomatic or flue-like symptomso Chronic lesions in lungs give TB-like picture

• In immunosuppressed personso Disseminated infection o Febrile illnesso Enlargement of RE system,

hepatosplenomagalyo Ulcerated lesions on tongue in AIDS patients

Histoplasmosis

Lab Diagnosis• Direct examination of sputum • Not helpful as few organisms in sputum• Bone marrow aspirate histology : • Oval yeast cells within macrophages by Giemsa

stain• Culture on Sabouraud’s Dextrose Agar incubate

at 25oC & 37oC to show dimorphic forms• Serology

o An Ab titre of 1:32 with yeast phase Ags is considered diagnostic

• Histoplasmin skin test: Epidemiological value only

• Histopathology of BMA: to see parasitic yeast form

Histoplasmosis

Oral lesions following hematogenous dissemination

Macroconidia and microconidia. Phase contrast

microscopy, potato glucose agar, slide culture, 25C.

Rough-walled macroconidia, Sabouraurd glucose

agar, 25C, lactophenol cotton blue preparation.

Yeast form growing at 37C in the laboratory. Phase contrast microscopy, 37C, 630X

Treatment• Oral itraconazole

• Disseminated diseaseo Amphotericin Bo Fluconazole in meningitis

• May need surgical resection of pulmonary lesions

Histoplasmosis

BLASTOMYCOSISPathogenesis

• Blastomyces dermatitidis • Dimorphic fungusPathogenesis• Inhalation of infectious particles• Cutaneous inoculation• Infiltration of macrophages and

neutrophils and granuloma formation

BLASTOMYCOSIS Clinical findings

• Asymptomatic • Pulmonary infection • Chronic skin infection • Subcutaneous nodule & ulceration• Disseminated infection • Bone, GUT, CNS, spleen

Broad based budding yeast

cells, KOH, from a lung

Broad based budding and thickened cell walls and globose shape are

characteristic of the yeast form of

Blastomyces dermatitidis.

Colony of Blastomyces dermatitidis on Mold Inhibitory Agar after14 days, 30C.

Skin lesion following dissemination from the lungs.

The cutaneous lesion developed following dissemination of the fungus from the lungs.

Treatment

• Amphotericin B• Azoles are alternative in immuocompetent

patients

Cryptococcosis

Causative agent Cryptococcus neoformans (5µ)o A typical yeast with a thick

capsule (25µ)o Urease positiveSource of infection• Pigeon or birds droppings &

contaminated soil

India Ink Preparation

Pathogenesis• Capsule is the virulence factor (antiphagocytic)

• Human infection by inhalation

• Most infections are asymptomatic

• May develop pneumonia

• Disseminate to CNS causing meningitis

Cryptococcosis

Clinical Features• Disease usually affects immunocompromised• Lung infection usually asymptomatic• Cryptococcal meningitis

o Among top four life-threatening infections in AIDSMeningitis• Intermittent headache & dizziness & vomiting• Difficulty in thinking• Slight fever • Slowly progressing to weight loss, impairment of

nerves • May be difficult to diagnose in early stages

Cryptococcosis

Lab Diagnosis• CSF Examinationo Turbid CSFo Decreased glucose & increased

proteino Increased cell count >100 cells

mostly lymphocyteso India Ink preparation

Yeast cell with a thick capsuleo Periodic acid-Schiff (PAS), detect

fungal elementso Culture on SDA (grows in 48-72 hrs)o Capsular Antigen in CSF by latex

agglutination

Cryptococcosis

India Ink Preparation

Negative cryptococcal

antigen latex test

Mixed culture of C. neoformans and C. albicans showing the distinctive brown colonies of C. neoformans, due to the selective absorption of pigment from the

media, compared to the white colonies of C. albicans.

Encapsulated yeast in India ink preparation.The small round structure in the center of the white area is the yeast

cell. 400X.

India ink preparation of CSF from a patient with cryptococcal meningitis

showing a budding yeast cell of C. neoformans surrounded by a characteristic wide gelatinous capsule.

Raised skin lesions resulting from dissemination of the

yeast in an immunocompromised patient.

C. neoformans yeasts in lung tissue. Gram stain, 100X

Treatment

• Systemic fungal agents that cross blood brain barrier (BBB)

• Fluconazole as prophylaxis in AIDS patients

• Combined Amphotericin B & flucytosine

Cryptococcosis

COCCIDIOIDOMYCOSIS

Causative agentCoccidioides immitis

Microscopy

37°C: Spherules filled with endospores

25°C: hyphae, barrel-shaped arthroconidia

COCCIDIOIDOMYCOSISPathogenesis

• Inhalation of the infectious particle, arthroconidia and spherule formation in vivo

• Engulfment within phagosomes by alveolar MQs

• Activation of macrophages (phagosome-lysosome fusion) leads to killing

• Immune complex formationdeposition leading to local

inflammatory response

COCCIDIOIDOMYCOSIS Clinical findings

PRIMARY INFECTION Asymptomatic in most cases Fever, chest pain, cough, weight loss Nodular lesions in lungs

SECONDARY (DISSEMINATED) INF. (1%) Chronic / fulminant Infection of lungs, meninges, bones and skin

COCCIDIOIDOMYCOSIS Diagnosis

Samples: Sputum, tissue

1. Direct examination (KOH; H&E)

2. Culture SDA: Mould colonies at 25 °C Spherule production in vitro by incubation in an enriched medium at 37°C, 20% CO2

Alternating arthroconidia. Note annular frill at both ends of the separated arthroconidia. Phase contrast

microscopy, tease mount from colony, 25C

Sherules and endospores in lung tissue. 1000X.

Alternating arthroconidia and hyphae. Lactophenol blue

mount, tease preparation of mould colony, 25C.

The rash is a immunologic response to the fungus. It is most commonly seen in caucasion women.

• Amphotericin B• Itraconazole• Fluconazole (particularly for

meningitis)

COCCIDIOIDOMYCOSIS Treatment

Organism Culture at 25 0C Culture at 370C Tissue Primary disease

Disseminated disease

C.neoformans Ecapsulated yeast Ecapsulated yeast Ecapsulated yeast pneunonia C. meningitis

H. Capsulatum Mold, tuberculate macroconid

Small yeast Small intracellular yeast

Pneumonia, hilar adenopthay

RES enlargement

B. dermatitidis mold yeast Small yeast pneunonia Skin and bone lesions

C. immitis Mold, arthroconidia

spherules spherules Vally fever Pneumonia,

meningitis

Skin & bones

P. brasiliensis mold yeast yeast pneunonia Skin and RES

Features of systemic fungal pathogens

Case presentation

A 52 years-old male arrived at an emergency room in a disoriented and poorly responsive state with difficult breathing. The patient’s history included poorly controlled diabetes and chronic obstructive pulmonary disease secondary to cigarette smoking. Current medications included steroids his pulmonary disease. Physical examination showed that the patient was slightly febrile, lethargic, and in respiratory failure. He showed deteriorating mental status, and a diagnosis of meningitis was considered . A lumber tap produced a CSF sample that on direct smear using calcofluor reagent showed encapsulated budding yeast. Despite aggressive therapy with amphotericin B and 5-flucytosine, the patient’s condition failed to improve. The patient died on the third day of hospitalization.