Lecture 11 Clinical Mycology PDF

Introduction to Mycology ▪ Mycology ▪ branch of biology concerned with the study of fungi, including their genetic and biochemical properties, their taxonomy and their use to humans as a source for tinder, medicine, food, and entheogens, as well as their dangers, such as toxicity or infec...

Introduction to Mycology ▪ Mycology ▪ branch of biology concerned with the study of fungi, including their genetic and biochemical properties, their taxonomy and their use to humans as a source for tinder, medicine, food, and entheogens, as well as their dangers, such as toxicity or infection. (Wikipedia) ▪ Fungus ▪ (plural: fungi) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms.  CLINICAL MYCOLOGY http://www.plantpath.cornell.edu Fungi Overview ▪ Heterotrophs- dependent on absorption of organic carbon compounds from their habitat for their nutrition ▪ LACK chlorophyll (fungi are not plants) ▪ Saprobes (living on dead organic matter) and/or parasites (utilizing living tissue) ▪ External digestion: release digestive enzymes then bring the small molecules into the hyphae ▪ Contain membrane bound organelles ▪ such as nuclei, mitochondria, Golgi apparatus, endoplasmic reticulum, ribosomes, lysosomes, etc ▪ Two morphological forms ▪ Hyphae ▪ Multicellular; existing in webs of slender tubes called hyphae ▪ Hyphae filaments collectively make up the mycelium (aka mold) ▪ Hyphae can be septate (having cross-walls) or non-septate ▪ Can reproduce sexually or asexually ▪ Yeasts ▪ Unicellular ▪ Asexual reproduction ▪ Dimorphism- ability form either yeast or hyphae depending on growing conditions  Hyphae ▪ Branching, tubular filaments that collectively make up the mycelium ▪ Depending on species can contain septate divisions ▪ Aerial hyphae often produce asexual reproduction propagules termed conidia (synonymous with spores). ▪ Relatively large and complex conidia are termed macroconidia ▪ smaller and more simple conidia are termed microconidia. ▪ When the conidia are enclosed in a sac (the sporangium), they are called endospores. ▪ The presence/absence of conidia and their size, shape and location are major features used in the laboratory to identify the species of fungus in clinical specimens. Fungal Identification ▪ Macroscopic Identification ▪ Agar/media changes ▪ Mycelium characteristics ▪ Microscopic identification ▪ Fungi can be differentiated on the basis of the structure of the hyphae and the presence of spores ▪ PCR  Clinically Important Fungal Agents ▪ Cutaneous Mycoses ▪ Dermatophytes ▪ Microsporidium canis ▪ Microsporidium gypseum ▪ Trichophyton mentogrophytes veteriankey.com veteriankey.com ▪ Opportunistic Mycoses ▪ Systemic Mycoses (infections with fungi that are either common in ▪ Aspergillus fumigatus all environments or are part of the normal biota) ▪ Blastomyces dermatitidis ▪ Candida albicans ▪ Histoplasma capsulatum ▪ Malassezia spp. ▪ Sporothrix schenckii ▪ Coccidioides immitis ▪ Cryptococcus spp. www.aspergillus.org.uk www.amrls.cvm.msu.edu CUTANEOUS MYCOSES Dermatophytosis (aka. Ringworm) ▪ The clinical condition caused by dermatophytes ▪ Saprophytic mycelial-forming fungi ▪ Possess keratolytic properties which allow them to invade skin, nails, and hair ▪ Infectious among animals and potentially zoonotic Dermatophytes ▪ Can be classified based on habitat in which they are found ▪ Anthropophilic – confined to human beings ▪ Zoophilic – parasites of animals ▪ Geophilic- normally existing as free-living saprophytes in the soil ▪ M.gypseum is the only known geophilic species that can be seen as an opportunistic pathogens in animals ▪ These geophilic species pose difficulty with diagnosis because they must be differentiated from zoophilic spp ▪ More then 3 dozen different organism within the genera of Microsporum and Trichophyton ▪ Most commonly seen species in veterinary medicine are ▪ Microsporum canis ▪ Microsporum gypseum ▪ Trichophyton mentagrophytes ▪ Microscopic evaluation is a MUST due to potential for bacteria and non-pathogenic fungi to cause color change on Sabrouraud dextrose agar. ▪ Clear cellophane tape is pressed on to center of colony and placed sticky side down onto microscope slide that has a drop of lactophenol cotton blue on it ▪ Slide is then examined at high dry powered lens. veteriankey.com Dermatophyte Testing ▪ Wood’s Lamp ▪ Ultraviolet light source (warm > 5mins prior to use) ▪ May be used to screen suspect lesions ▪ Some species of Microsporum with fluoresce a clear apple-greed ▪ Fluorescence is only evident in 50% of cases involving M. canis ▪ Lack of fluorescence does NOT rule out the possibility of ringworm Microscopic Visualization without culture Mounting in 10% KOH or KOH/DMSO combo DMSO prevents need to warm the slide Hair follicles plucked and placed on slide with 1-2 drops of KOH or KOH/DMSO After about 2-10 mintus small globular arthrospores attached to hair shaft are visible if positive  Dermatophyte Testing ▪ Culturing via DTM (Dermatophyte Test Medium) ▪ aka Sabouraud’s Dextrose Agar ▪ Contains ▪ nitrogenous and carbonaceous (soy peptone) for fungal growth ▪ dextrose for energy metabolism ▪ nitricycloheximide, gentamicin, and chlortetracycline to inhibit bacterial and unwanted saprophytes ▪ a pH indicator (Phenol red) ▪ Interpretation ▪ Dermatophytes preferentially metabolize proteins before carbohydrate ▪ Protein metabolism releases alkaine metabolites ▪ Saprophytic fungi metabolize carbohydrates first ▪ Carbohydrate metabolism releases acidic metabolites ▪ Thus if dermatophyte growth present should see grow AT THE SAME time as media color change ▪ Saprophytes will eventually metabolize protein to create alkaline metabolites yielding color change but growth will have occurred prior ▪ Dermatophyte colonies are white, light yellow, tan, or buff-colored with a fluffy, cottony to powdery appearance ▪ Dermatophytes are NEVER black, green, or gray  Microsporum canis veteriankey.com mycology.adelaide.edu.au Microsporum gypseum http://thunderhouse4-yuri.blogspot.com Trichophyton mentagrophytes veteriankey.com Macroconidia - laterally directly on the hyphae or on short pedicels, and are thin- or thick-walled - clavate to fusiform - 4-8 x 8-50 μm in size https://mycology.adelaide.edu.au Yeasts ▪ Candidia spp. ▪ commensal of mucous membranes and the gastrointestinal tract ▪ ovoid, budding yeast cells (2–4 μm in diameter) with thin walls, or they occur in chains that produce pseudohyphae when the blastospores remain attached after budding division ▪ Malassezia ▪ part of the normal skin flora of humans and animals ▪ M. pachydermatis is known to cause external otitis in dogs amrls.cvm.msu.edu SYSTEMIC MYCOSES  Aspergillosis ▪ Caused by Aspergillus spp. ▪ An opportunistic pathogen found world wide ▪ dead leaves, stored grain, compost piles, or in other decaying vegetation. It can also be found on marijuana leaves ▪ Primarily causes respiratory infection that may become generalized; however, tissue predilection varies among species ▪ Horses: guttural pouch mycosis ▪ Cattle: mycotic abortion, mastitis ▪ Birds : air sac infections ▪ Dogs: typically localized to the nasal cavity or paranasal sinuses and is usually caused by infection with A. fumigatus www.aspergillus.org.uk Blastomycosis ▪ Caused by Blastomyces dermatitidis ▪ Dogs more susceptible than other species ▪ Increase prevalence in certain geographic regions (river basins, great lakes) ▪ Mississippi, Ohio, Missouri River Valley ▪ Inhalation of spores→settle in airway and reproduce ▪ Can spread to other parts of the body ▪ Clinical signs ▪ Pulmonary Disease ▪ Fever, wt loss, hyporexia ▪ Diagnosis ▪ Cytology ▪ Urine antigen testing ▪ PCR ▪ Suspected by finding “snowstorm” pattern on radiographs Histoplasmosis ▪ Caused by Histoplasma capsulatum ▪ found worldwide ▪ Endemic to areas of the USA (Mississippi & Ohio River Valleys) ▪ Dimorphic ▪ Dogs and cats most commonly infected ▪ Inhalation ▪ Lungs and thoracic LN primary sites of infection > GI ▪ Clinical signs ▪ Nonspecific ▪ Emaciation, cough, fever, diarrhea, enlargement of LN, spleen, and liver ▪ Can be fatal (esp. acute form) ▪ Diagnosis ▪ Cytology ▪ Tissue Bx ▪ Antigen testing via ELISA on urine, serum, and CSF Coccidioidomycosis (aka Valley Fever) ▪ Caused by Coccidiodes immitis ▪ Dimorphic fungus ▪ Found in arid to semiarid regions of southwestern USA ▪ Epidemics occur when rainy periods are followed by drought ▪ Dogs most susceptible veterinary species ▪ C.S. ▪ Primarily respiratory disease ▪ Harsh cough, lethargy, ▪ Disseminated disease possible ▪ Cough, cachexia, fever, enlarged joints, intermittent diarrhea ▪ Diagnosis ▪ Demonstration of spherules in tissue ▪ Antigen testing insensitive Sporotrichosis (Rose Gardener’s Disease) ▪ Caused by Sporothrix schenckii ▪ Found worldwide ▪ Cats can serve as a source of zoonosis ▪ Three forms ▪ Lymhocutaneous- most common ▪ Cutaneous ▪ Disseminated Chytridiomycosis ▪ Caused by Batrachochytrium dendrobatidis & B. salamandrivorans ▪ Chytrid fungi (zoosporic) ▪ Can survive for weeks in water depending on temperature ▪ Infectious disease of amphibians ▪ infects keratin layer of the skin where it multiplies ▪ Clinical signs ▪ Anorexia ▪ Lethargy ▪ Loss of righting reflex ▪ Discoloration of skin