Mycoses Flashcards
Sporangiospore
fungal spore formed by asexual reproduction. formed within a sporangium on an aerial hyphae called a sporangiophore
Conidia
fungal spore formed by asexual reproduction. formed on conidiophore
Zygospore
fungal spore from sexual reproduction. Develops in thick-walled zygosporangium, formed from the fusion of side projections of two compatible hyphae
Geophilic dermatophyte
dermatophyte that inhabits soil in association with decomposing keratinous material
Zoophilic dermatophyte
obligate pathogen in animals
Anthropophilic dermatophyte
obligate pathogen of humans
Dermatophyte important causal agents
Microsporum, Trichosporum, Epidermophyton
Microsporum general characteristics
invades hair and skin
thick-walled, multi-septated macroconidia
microconidia are stalked, clavate or arranged singly along hyphae
M. canis most common in domestic animals
Trichophyton general characteristics
Invades hair, skin, nails, horns, claws
Thin walled and smooth macroconidia, cylindrical to cigar shaped. Typically more severe than Microsporum infections
Dermatophytosis clinical signs
alopecia, erythema, scaling, crusting, annular-ringed lesions, vesicles or papules
Dermatophytosis transmission
- Arthrospores shed by infected animals are viable in the environment (months to years)
- direct contact with infected animal
- exposure to arthrospores in the environment/fomites
Dermatophytosis pathogenesis
Dermatophytes –> enter stratum corneum –> release proteases –> cause inflammation –> movement away from site of infection to nearby follicle –> central healing causes ringed lesion
Canine ringworm genuses
M. canis, M. gypseum, T. erinaceid, T. mentagrophytes
Canine ringworm lesions
brittle hair, dry and scaly skin, crusts and scabs
Kerion –> specific lesion due to T. mentagrophytes (intense inflammation, swelling, ulceration, prurulent exudate)
Canine predispositions to ringworm
Compulsive diggers (gypseum), good rat catchers (mentagrophytes), avid hedgehod worries (erinaceid)
Feline ringworm
M. canis –> main genus, cats are reservoir
Often asymptomatic (public health risk)
Lesions: circular areas of stubbed hair, alopecia, mild scaling and folliculitis at the head
Most common in kittens with immature immune systems and adults with immune deficiencies.
Feline otitis
persistent waxy, ceruminous, otic discharge caused by M. canis
Bovine ringworm
Trichophyton verrucosum.
Calves are more susceptible and incidence is higher in winter.
Lesions: circular, scattered, accompanied by skin scaling and alopecia, large plaques may develop with the formation of thick scabs and crusts, severe inflammation, pruritus (secondary bacT infections?)
Spontaneous resolution
Porcine ringworm
Microsporum nanum
Common disease, affects large breeds. Higher incidence with high density and humidity, poor sanitation
Lesions: circular, roughened, mildly inflamed. anywhere on body
Equine ringworm
T. equinum, M. gypseum
Lesions: multiple, dry, scaly, raised lesions on any body part. Inflammation and exudates cause hair to mat together and enlarged lesions create a moth-eaten appearance
Infections often become chronic and subclinical and recur under stress
Avian ringworm/favus/white comb
M. gallinae
Lesions: white patches on the comb of infected male birds
Occasionally, disease spreads into the feathers
Wood’s lamp
dermatophytosis diagnostic technique - 50-60% of M. canis infections test positive under UV light. Use fluorescing hairs for sampling
Direct microscopic exam for dermatophytosis
examine hairs from lesions/scales. Use 10-20% KOH. Fine hyaline septate hyphae in keratin scales and in hair shafts. Arthroconidia see on hair.
Dermatophyte Test Medium (DTM)
Growth with red slant before 10 days - dermatophyte
Growth with yellow slant that turns red after 10 days - non dermatophyte.
Medium provides peptones for protein, antibiotics, dextrose sugar, cyclohexamide to inhibit sapprophytes
Incubate at 25-30 degrees
M. canis on culture
spreading whitish and cottony surface. Golden-yellow reverse pigment.
Physiological tests for dermatophytes
temperature tolerance, urease production, in vitro hair perforation test for Trichophyton
Treatment for dermatophytes
remove/kill fungus from skin/hair (clip, shampoos, dips, sprays, topical antifungals). Systemic therapy: azoles
Treat until 3 negative cultures
control/prevention for dermatophytes
clean up environment and fomite sources (vacuum, wash bedding, etc.) use 10% bleach solution. Vaccination is effective for bovine ringworm.
Zoonotic dermatophytes
M. canis and T. verrucosum
Dermatomycoses important causal agents
Malassezia, trichosporon, geotrichum candidum
Malassezia
M. pachydermatis
lipophilic yeast, opportunistic pathogen (part of normal microbiome on the skin)
Otitis externa (malassezia)
clinical signs: head shaking, pruritus, bad odour, chronic otitis
Diagnosis: otoscopic exam of ear canal, cytology for bacteria, yeast and mites
Treatment: treat predisposing factors, topical antifungals and systemic antimicrobials
Seborrheic dermatitis (definition + CS)
superficial dermatitis as a regional disease affecting ventral abdomen, face, feet, neck. perineum, leg folds or generalized disorder
Clinical signs: face rubbing, foot licking, erythematous skin, scaly skin, alopecia, hyperpigmentation, lichenification
Seborrheic dermatitis predispositions
breed: poodles, spaniels, chihuahuas, german shepherds, boxers, basset hounds
others: allergies, seborrhea
Seborrheic dermatitis diagnosis, treatment
history of poor response to therapies, demonstration of yeast on skin scrapes (rule-out system). Most useful is cytology of affected areas looking for slightly elongated, oval, broad-based yeast
Treatment: remove predisposing factors, shampoo/creams/dips with selenium sulfide/ketoconazole, oral ketoconazole
Trichosporon
causes nasal mass in cats. Treatment is to remove the mass surgically and follow up with oral ketoconazole
Geotrichum candidum
more found in exotic animals. Often isolated from feces of healthy/clinically normal animals. Causes cutaneous lesions, nodular, well-circumscribed dermo-epidermal masses
subcutaneous mycoses general characteristics
infections of deep skin, muscle, bone or CT. Associated with injured tissues.
Etiologic agents: soil/decaying vegetation, dematiaceous or hyaline molds and dimoprhic fungi
infections are chronic
Important causative agents of subcutaneous mycoses
Sporothrix schenckii, histoplasma capsulatum var. farciminosum, dermatiaceous fungi
Sporotrichosis characteristics
dimorphic, dermatiaceous.
yeast at 37 degrees - cigar shaped, pleiomorphic budding yeast.
mold at 25 degrees - thin septate hyphae with conidia in a rosette-cluster
found in soil, vegetation, peat moss and wood
Conidia enter the skin through puncture wounds from thorns or bites
Sporotrichosis geography
most common in in tropical and subtropical america
Sporotrichosis lesions
subcutaneous nodules that ulcerate and heal. lesions are not painful or pruritic. Disease may follow lymphatic vessels
Sporotrichosis CS in dogs
Cutaneous: localized, multicentric
Lymphocutaneous: nodules along lymphatics
Disseminated: rare, possibly fatal
Sporotrichosis pathogenesis
conidia or mycelia enter through broken skin –> change from mycelial form to yeast or parasitic form –> virulence factors (thermotolerance, acid phosphatases, proteinases) –> lymphocutaneous manifestation –> infection spreads along lymphatics
Diagnosing sporotrichosis with LM
Under LM: look for yeast (in macrophages). Cat lesions tend to have more yeast
Diagnosing sporotrichosis with culture
mold colonies are cream coloured, wrinkled and leathery. Will turn black/grey with age.
Yeast colonies are soft and white to cream coloured
Sporotrichosis treatment
Iodide (not for cats), azoles, Itraconazole for cats
Sporotricosis zoonosis
most human cases occur through shedding from cats (scratch, bite).
Prophylaxis: care in handling rote wood, plant material and infected animals
Epizootic lymphangitis
Histoplasma capsulatum var. farciminosum
Dimorphic fungus.
Yeast: pear shaped, double contoured budding yeast in macrophages/neutrophils
Can be isolated from soil enriched with bird or bat feces
Infection acquired by wound infection or transmission by blood sucking insects
Epizootic lymphangitis host
equids
Epizootic lymphangitis lesions
granulomatous, nodular lesions with a tendency to ulcerate in skin, subcutaneous tissue, along lymph vessels
Chromoblastomycosis
chronic fungal infection in cats and humans. Dermatiaceous fungi form thick walled-muriform cells (sclerotic bodies).
CS: firm, protuberant, warty, ulcerative nodules (on feet and legs)
Eumycotic mycetoma
Limited to one area of the body.
CS: swelling, fistulas, grains or granules in exudate. SubQ swellings with draining tracts, may resemble chronic abscess.
Chronic mycetoma – fistulous tumour
may cause osteomyelitis
Phaeohyphomycosis
saprophytic, pigmented fungi that appear in lesions as dematiacous, septate hyphal forms (no granules).
Found in dogs and cats
CS: pustules, abscesses, granulomas, shallow ulcerated or open lesions
Bovine nasal granuloma
Granulomatous swellings in the nasal cavity and trachea of cattle.
CS: dyspnea, inspiratory stridor, nasal discharge. Pink-white polyps visible on endoscopy
Bovine nasal granuloma diagnosis
direct exam of crushed polyp – dematiaceous fungi
culture – white colonies that become olive green, brown or black with dark reverse pigment
systemic mycoses primary SOI
lungs
systemic mycoses important causative agents
Blastomyces dermatitidis (dimorphic), coccidioides immitis (dimorphic), histoplasma capsulatum var. capsulatum (dimorphic), cryptococcus neoformans (yeast)
Blastomycosis
Blastomyces dermatitidis.
Affects cats, dogs, humans
Moves from lungs to skin, eyes and bones
Blastomycosis lesions
few to numerous, variable sized, irregular, firm, grey to yellow areas of pulmonary consolidation and nodules in lungs and thoracic lymph nodes
Cutaneous lwesions – single or multiple papules or chronic draining, nodular pyogranulomas
Blastomycosis pathogenesis
Aerosolized mycelial fragments or spores from the environment are inhaled. These are deposited in alveoli of a susceptible host. The mature yeast develop and grow intracellularly as large budding yeast. May spread from the lungs via lymph/blood vessels
Blastomycosis distribution
Highly endemic in North America –> Ohio, missouri, tennessee, mississippi river valleys, st. lawrence river area, great lakes
Blastomycosis clinical signs
coughing, dyspnea, dry and harsh lung sounds, anorexia, depression, lameness, lymphadenopathy, skin lesions (predominant in cats), ocular lesions
Blastomycosis diagnosis
clinical signs, history.
Samples: tissues, tracheal wash, lymph node biopsy, cutaneous lesion exudate or biopsy
Microscopy: spherical, thick walled, large, broad-based budding yeast
Culture: mold culture is severe biohazard
Blastomycosis treatment
Itraconazole for dogs, amphotericin B for chronic/tough cases
Blastomycosis zoonosis
zoonotic transmission is uncommon but can happen from contaminated knives or dog bites. PPE important!
Coccidiomycosis (San Joaquin Valley Fever)
Coccidioides immitis.
Dust-borne, not contagious
Humans, dogs, llamas affected
Primarily a chronic respiratory disease can spread to eyes, bones and joints
Not zoonotic, but can mycelial phase can form on bandages of draining lesions
Coccidiomycosis pathogenesis
Arthroconidia in the environment mature into mycelia which fragment into arthrospores. Infection is via inhalation of arthrospore which causes transition into a spherule. spherule matures with production and release of endospores. Endospores will travel in lymph/blood
Coccidiomycosis distribution
Infections are in semi-arid regions of the SW USA (arizona, california, new mexico, texas, utah, nevada) and sikmilar areas of central and south america
Coccidiomycosis clinical signs
anorexia, cough, weight loss, lameness, abscesses, draining tracts, lymphadenopathy, meningitis
Coccidiomycosis diagnosis
CS and history
Samples - draining lesions and biopsies or fine-needle aspirate of infected tissue (ook for classic spherules
Culture - mycelial form very hard to handle. Mold have hyaline hyphae and alternating, barrel-shaped arthroconidia
Coccidiomycosis treatment
long term treatment (8-12 weeks) with azoles, amphotericin B if needed
Histoplasmosis
Histoplasma capsulatum var. capsulatum
chronic, non-contagious, disseminated, granulomatous disease of humans and animals
mainly in dogs and cats under 4
Histoplasmosis lesions
enlarged liver, spleen and mesenteric lymph nodes. Ascites, yellow-white variable-sized, granulomatous nodules in the lungs enlarged bronchial LNs, foci of granulomatous inflammation on liver, myocardium and SI
Histoplasmosis pathogenesis
inhalation or ingestion of microconidia or hyphal fragment from environment, conversion to yeast in vivo, yeast replicate, may spread via lymph/blood to spleen, bone marrow
Histoplasmosis distribution
humid environments with highly nitrogenous soils (contaminated with bird/bat shit).
High risk areas: bat caves, old chicken houses
Regions: tennessee, ohio, mississippi, missouri, st lawrence river area
Histoplasmosis clinical signs
pulmonary infection predominant, chronic disease (inappetance, weight loss, fever), enlarged LNs, anemia, GI problems in dogs
Histoplasmosis diagnosis
clinical signs and history
samples: buffy coat smear, LN aspirate, rectal scraping, biopsies, bone marrow aspirate. Yeast are small in macrophages, basophilic center and clear halo
Cultures are a severe biohazard
Histoplasmosis treatment
long-term treatment (4-6 months min) with azoles. Amphotericin in combination with oral azole for severe cases.
