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Fungus Part II

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Medical Mycology

Medical Mycology

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  • 1. PRAVEG GUPTA
  • 2.  There are four main fungal infections in superficial mycoses: Tinea versicolor (Pityriasis versicolor) –skin Tinea nigra – skin Black piedra – hair White piedra – hair
  • 3.  Malassezia furfur. 7 species of malassezia have been identified out of which M.furfur is the commonest. Lipophilic fungus found in areas of body rich in sebaceous glands. Macroscopy – dry chalky appearance. Microscopy – bottle shaped budding yeast cells. Spaghetti and meat balls appearance.
  • 4. : TINEA NIGRA Superficial asymptomatic skin disease characterised by light brown to black macular areas affecting thickly keratinised regions of palmar and plantar stratum corneum. Exophila wernikii. For microscopy KOH mount is done and fur culture sabouraud’s agar is used.
  • 5.  White and black piedra: Nodules are formed on hair shaft. White piedra - tricosporon bigelli. Characterised by white nodules on hair shaft of axilla. Blackpiedra - piedraia hortae. Characterised by black nodules on hair shaft of beard and scalp.
  • 6.  They are fungal infections of skin, hair and nails which are generally restricted to keratinised layers of skin and its appendages. Dermatophytoses is also called tinea or ringworm. As the lesions are often circular, they are called ringworm. The term tinea (latin=worm) describes the serpentine and annular (ring like) lesions that resemble a worm burrowing at the margin.
  • 7.  Hyphae and arthrospores of dermatophytes are present in lesions while in cultures they appear as septate hyphae and asexual spores. Three genera are differentiated based mainly on the nature of macroconidia. Genus Macroconidia Epidermophyton club shaped Microsporum spindle shaped Trichophyton pencil shaped Examples of dermatophytes: T.rubrum, T.tonsurans, T.mentagrophytes, T.violaceum, M.audouinii, E.flucossum.
  • 8.  Endothrix: arthrospore formed within hair shaft resulting in break off of hair. Eg T.violaceum, T.tonsurans. Ectothrix: arthrospore formed outside the hair eg. M.audouinii. Favus: T.schonleinii causes favus. Fungal activity is minimal in hair shaft but intense growth occurs within and around follicle. This produces characteristic honey comb appearance on scalp. Genus target site Epidermophyton skin and nails Microsporum skin and hair Trichophyton skin, hair and nails Classification of dermatophytes based on habitat: Anthrophilic dermatophytes Zoophilic dermatophytes Geophilic dermatophytes
  • 9.  Classification of ringworm based on site: Tinea capitis = ringworm of scalp Tinea corporis = ringworm of non hairy skin of body Tinea cruris = ringworm of groin, perineum Tinea barbae = (barber’s itch) bearded areas of face Tinea pedis = (athletic foot) toe clefts
  • 10.  Nail samples: must include clippings from any discoloured, dystrophic or brittle parts of nail and scraped material from underneath the nail preferably from its edges. Scales from skin lesions: using blunt scalpel, the skin lesion is scraped outward from the edges of the lesions where most viable fungus is likely to be present. Specimens from scalp must include hair stubs, contents of plugged follicles and skin scales.
  • 11.  Infected hair: are plucked from scalp using forceps. Cut hair are not suitable as the infection is most likely near the scalp area of hair. Hair brush sampling technique: sample may be collected from scalp by brushing with a sterilized plastic hair brush or scalp massage pad which is then inoculated into culture medium by pressing the brush or pad spines into sabouraud’s agar. Microscopy: KOH mount Culture: Sabouraud’s dextrose agar. Identification: is done by studying microscopic and macroscopic features.
  • 12.  Three genera are recognised: Epidermophyton: Smooth thin-walled Macroconidia only present, no microconidia, colonies a green-brown to khaki colour. Microsporum: Macroconidia with rough walls present, microconidia may also be present. Trichophyton: Microconidia present, smooth-walled macroconidia may or may not be present.
  • 13.  Causative fungi: Cryptococcus neoformans Histoplasma capsulatum Blastomyces dermatitidis Coccidioides immitis Paracoccidioides brasiliences
  • 14.  Cryptococcus is a yeast and occurs worldwide. The other four are dimorphic fungi infrequently found in India. Infection of systemic fungi is acquired via lungs by inhalation and primary focus of infection is lungs. The disease is asymptomatic in most cases, but severe in immunocompromised. Reactivation of latent infection is possible.
  • 15.  Definition: It is a subacute or chronic infection caused by capsulated yeast cryptococcus neoformans. Reservoir: cryptococcus is a ubiquotous saprophyte often found in bird droppings, esp. of wild birds (pigeon, chicken) and soil. Occurrence of infection: throughout world, more in I/C eg AIDS.
  • 16.  Morphology: spherical budding yeast cell having prominent polysaccharide capsule. 4 serotypes are known – A,B,C and D. Virulence factors: antiphagocytic polysaccharide capsule, melanin produced by cells. Route of infection: usually inhalation, esp. of dust containing excreta of pigeons. Clinical features: primary and symptomless granuloma of lung, cryptococcal meningitis, skin and other infections, lung infections.
  • 17.  Laboratory diagnosis: Specimen: CSF, biopsy, urine. Microscopy: Indian ink preparation shows capsulated yeast cells. Culture: sabouraud’s dextrose agar shows creamy white mucoid colonies. Urease test: +ve Carbohydrate assimilation test Direct immunofluorescence test Latex agglutination test for antigen detection.
  • 18.  Causative organism: histoplasma capsulatum Target site: Reticuloendothelial system Reservoir: soil, bird and bat droppings. Route of infection: inhalation of spores Clinical features: acute pulmonary histoplasmosis, chronic pulmonary disease, disseminated disease, ocular histoplasmosis.
  • 19.  Laboratory diagnosis: Specimen: sputum, biopsy Microscopy: KOH mount, giemsa stain, wright stain. Culture: sabouraud’s dextrose agar, brain heart infusion agar. Findings: white cottony mycelium, macroconidia, microconidia. Histoplasmin skin test CFT, latex agglutination tests, precipitation tests, histopathology.
  • 20.  Causative organism: blastomyces dermatitidis Reservoir: soil containing organic debris eg animal droppings, rotting wood and plant material. Route of infection: inhalation of conidia Persons at risk: persons collecting firewood or working in tearing of old buildings. Clinical disease: primary pulmonary disease, chronic cutaneous blastomycoses, disseminated disease. Laboratory diagnosis: KOH mount, giemsa stain, PAS stain, H&E stain, sabouraud dextrose agar, antigen detection tests.
  • 21.  Causative organism: coccidioides immitis Reservoir: desert soil, rodent burrows, archeological structures Route of infection: inhalation of spores Persons at risk: agricultural workers Clinical disease: primary pulmonary disease, meningitis, skin and soft tissue infections.
  • 22.  Laboratorydiagnosis: Specimen = sputum, biopsy, pus etc. Microscopy = spherules and endospores in KOH mount are pathognomonic. Culture = sabouraud’ dextrose agar Serology, histopathology, skin tests.
  • 23.  Causative organism: paracoccidioides braziliensis Route of infection: inhalation of spores Reservoir: soil with high humidity Clinical disease: pulmonary infection, mouth, nose, lymph nodes, skin, adrenal gland, GI tract etc.
  • 24.  Laboratory diagnosis: Specimen: sputum, crusts, pus, biopsy Microscopy: KOH mount Culture: sabouraud’s dextrose agar CFT, immunodiffusion tests
  • 25.  Introduction: Some saprophytic fungi of environment that usually do not produce disease may cause infection under special conditions such as in immunologically compromised patients and in terminal stages of chronic disease. As these fungi take advantage of the debilitated state of the individual to become pathogenic, they are referred to as opportunistic fungi. The incidence of these fungal infections has increased in AIDS and with wide use of antibiotic, steroids, and immunosuppressive drugs.
  • 26.  Yeast: cryptococcus Yeast like fungi: candida, torulopsis Filamentous fungi: Aspergillus Mucor Rhizopus Absidia Cephalosporium Fusarium Penicillium Geotrichum Others: pneumocystis carinii
  • 27.  Candidiasis is a major disease problem in immucocompromised patients in AIDS and after prolonged antibiotic therapy and invasive surgery. Medically important species: C.albicans, C.stellatoidea, C tropicalis, C.krusei, C.gullermondii C.viswanathii C.glabrata C.parapsilosis
  • 28.  Morphology: spherical or oval budding yeast cells, pseudohyphae, pseudomycelium, blastospores. Commensalism: candida occur as commensals in human body at sites like intestine, oral cavity, vagina, rectal area. Mode of infection: endogenous or exogenous Predisposing factors: DM, immunodeficiency including AIDS and malignancy.
  • 29.  Lesions: Mucous membrane: oral thrush, vaginal thrush. These are white patches on the mucosal surface. Skin: moist areas of skin like axilla, groin, perineum, submammary folds, toe clefts etc are affected commonly. Nails: infection of finger webs, nail folds, nails. Occurs as reddened swelling. ASSOCIATED WITH FREQUENT IMMERSION OF HANDS AND FEET IN WATER. Chronic mucocutaneous candidiasis Systemic candidosis: endocarditis, organs like lungs kidneys etc affected.
  • 30.  Laboratory diagnosis: Microscopy: KOH mount, gram stain Culture: sabouraud’ dextrose agar shows creamy white smooth colonies with yeasty odour. Germ tube test: candida albicans grown in human serum at 37 C for 3 hours when examined in KOH shows filamentous outgrowths (germ tubes). Chlamydospores develop in nutritionally poor medium like corn meal agar at 28 C. Serological tests Skin tests
  • 31.  Introduction: worldwide distribution Spores are very commonly seen in soil, food, paint, air vents, disinfectants even. Main species: A.fumigatus A.flavus A.niger A.terreus A.nidulans A.glaucus
  • 32.  Aspergillus asthma Bronchopulmonary aspergillosis Aspergilloma = often called fungus ball in which fungus colonises in preexisting cavities (often tuberculous, sometimes bronchiectatic) Disseminated aspergillosis Superficial infections
  • 33.  Microscopy: KOH mount shows septate mycelium with characteristic dichotomous branching Culture: SDA shows velvetty powdery colonies. Skin tests serology
  • 34.  P.carinii is a unicellular eukaryotic organism with tropism for growth on respiratory surface of mammals. Originally classified as a protozoan, it is now thought to resemble more to fungus. Transmission: droplet inhalation, close contact
  • 35.  Morphology: giemsa stain, methanamine silver stain are useful. Trophic form (trophozoite) 1.5-4 µm D Cystic form (sporocyst) 4-7 µm D Mature spore case is about 5 µm D containing 8 spherical oval to fusiform spores (1-3 µm D). Clinical features: In immunocompetent patients the infection is asymptomatic In immunocompromised patients it causes INTESTITIAL PNEUMONIA. It may also cause extrapulmonary manifestations.
  • 36.  Laboratory diagnosis: Specimen: aspirates of bronchial washings and sputum, percutaneous transthoracic needle aspiration, bronchoalveolar lavage. Microscopy:giemsa stain shows purple nuclei, cytoplasm light blue, cell wall as clear unstained area. Gomori methenamine stain shows cyst wall. Culture: NOT CULTIVABLE Immunofluorescence study.