Mycology Exam Objectives Flashcards
What is the infectious particle for Blastomyces dermatitidis?
Microconidia produced by mycelial form in soil
- is inhaled, penetrates wounds, or possibly ingested
Infectivity of Blastomyces dermatitidis
Not contagious or transmissible, not zoonotic!
- common environmental source if in more than 1 animal in a household
- vets may be infected from patients (common w/ open wounds) or from necropsy by handling infected tissues
What is the infectious particle for Histoplasma capsulatum?
Microconidia produced by mycelial form in soil
- disseminated by wind, easily inhaled/ingested
Infectivity of Histoplasma capsulatum
- aerosols from digging, chain saws, birds roosting on air conditioners have led to epidemics
- not transmissible, not zoonotic –> in vivo yeast phase does not survive long if shed from active infection (inclu. feces)
What is the infectious particle for Coccidioides immitis?
Arthroconidia (conidia)
- disseminated by dust storms, rodents, excavations
- inhalation, or may be inoculated into skin
Infectivity of Coccidioides immitis
Most virulent of all fungal pathogens!
- only a few conidia are required to produce infection
Infectivity of Sporothrix schenckii
Not contagious, but infected animal will serve as source of contamination of the environment
- people have been infected from cats
- cats may shed viable organisms in feces
- occupational disease of gardeners and florists
What is the infectious particle of zygomycetes?
Conidia
- inhalation, percutaneous routes, ingestion of conidia
What are the 2 orders of zygomycetes?
Mucorales and Entomophthales
Mucorales
Rhizopus, Mucor, Rhizomucor, Absidia, Cunninghamella, Mortierella, Syncephalatrum
- occur rarely, in immunocompromised hosts as opportunistic infection
Entomophthorales
Occurs in tropical and subtropical regions
- transmission via implantation of spores thru cutaneous trauma (insect bite, foreign bodies) and by inhalation of spores
- true pathogens! –> infect immunocompetent hosts
Infectious particles of Cryptococcus neoformans
Yeast cells
- found in surface dust and dirt, are inhaled and deposited on mucous membranes of nasal cavity
Infectious particle of Pythiosis
Aquatic, motile biflagellated spores
- ingested when a dog or horse drinks contaminated water
What is the most common manifestation of Blastomyces dermatitidis?
Pulmonary form!
- does not spontaneously resolve
- chronic respiratory problem with weight loss, fever that is non-responsive to antibiotics, dry (non-productive) cough, ocular problems, lameness, lymphadenopathy, pulmonary interstitial pattern that resembles tuberculosis (snow storm)
Which 2 fungi have pulmonary forms that spontaneously resolve?
Histo and coccidiomycosis!
Ocular form of Blastomycosis
Uveitis, panophthalmitis, glaucoma, acute retinal detachment –> irreversible blindness
Skin form of Blastomycosis
Ulcerative or granulomatous dermatitis
- usually found in animal with the pulmonary form, indicating extensive dissemination and poor prognosis
- granulomatous nodules and draining tracts
- greasy exudate and matted hairs around ulcerated skin
- common on: face, nose, lips, limbs, feet, pads and toes
Bone form of Blastomycosis
- lameness (single or multiple bones involved)
- invades osseous tissue
- concurrent lymphadenopathy of affected side
- osteolytic lesions at ends of long bones
Genitourinary form of Blastomycosis
Found in prostatic washes
- signs associated with prostatitis
- hematuria, pyuria
- yeast leave in the urine
Best way to make a definitive diagnosis of any fungal disease?
Demonstrate the organism and associate it to the lesions
Which fungal agent makes a capsule?
Cryptococcus neoformans
- narrow based budding yeast cells surrounded by polysaccharide capsule
Which agents exist in the GIT of birds and bats?
- Candidiasis
- Cryptococcus neoformans
Which agents do not occur in the GIT of birds and bats?
- Histoplasma capsulatum
What does Histoplasma capsulatum look like?
- in vivo: small, nonencapsulated, intracellular yeast cells (only intracellular yeast!)
- histopathology: will see 2-40 yeast cells within a single host cell = shrunken cytoplasm creating the appearance of a capsule
What are the geographic areas for dimorphic fungi?
- blastomycosis: MS and Ohio river basins, central Atlantic states
- histoplasmosis: worldwide, eastern US, MS river valley basin, great lakes, Northeast
- coccidiomycosis: limited to southwestern states
- sporotrichosis: worldwide, common in tropics and in the South
What is the defining feature of zygomycetes?
Coenoctic hyphae
- gametangia –> zygospore
- small heads (sporangia) near the edge of colongies
Which agents do mycotic placentitis?
- zygomycetes: cows caused by Mucor and Mortierella
- candidia
- aspergillosis
Order Mucorales disease
- mycotic ruminitis: calves (Absidia, Rhizopus, Mucor, Rhizomucor)
- mycotic placentitis: cows (Mucor and Mortierella)
Order Entomophthorales disease
- Conidiobolus coronatus: mucocutaneous sites = sinusitis, nasopharyngitis, URI in horse
- Basidiobolus ranarum: subq mycosis of the trunk and extremities in cattle and horses
Which agents are sensitive to cycloheximide?
Zygomycetes
- cannot be cultured on Mycosel agar or SDA with C&C
Cryptococcus neoformans
What is cycloheximide?
Added to agar to inhibit growth of saprophytic fungi
Where do agents exist in their reservoir form?
- dermatophytes: soil
- pythium: water
- zygomycetes: environmental saprophytes, laboratory contaminants
- cryptococcus: soil, dried pigeon droppings
- C. albicans: normal flora
- Malassezia: normal human flora and animal cutaneous commensal flora
- blastomyces: soil saphrophyte
- histoplasmosis: soil (moist, feces of birds), decomposing trees
- coccidiomycosis: soil (high temp, low humidity), around rodent burrows
- sporotrichosis: soil, wood. vegetation
What diagnostic test is run on Cryptococcus neoformans?
- direct smear with India ink
- culture on blood agar or SDA
- immunodiagnosis via direct agglutination of circulating capsular antigens in a latex bead test
Zoophilic dermatophytes
M. canis
- animals as their host and reservoir
Geophilic dermatophytes
M. gypseum, T. mentagrophytes
- soil as their reservoir
Anthropophilic
Fungus only found on humans, not animals!
- ex: Epidermophyton flocculosum
What 3 species of dermatophytes cause 99.9% of ringworm in dogs and cats?
- M. canis: 90% cats, 70% dogs
- M. gypseum: 20%
- T. mentagrophytes: 10%
Which animals amplify Sporotrichosis, so that when it is introduced back into the environment, it causes zoonosis?
Cats
What tissue is invaded with Dermatophytes and how far down does it go into the hair follicle?
Hair and skin
- only non-viable keratinous tissue is invaded!
- are non-invasive, do not survive in living tissues
- grow down anagen hair shaft to Adamson’s fringe –> where hair shaft exits the follicle
What dye’s are used to stain fungi?
- 10% KOH: used to clear host cells
- PAS: specific for all fungi –> hyphae stain bright red
- India ink
Do you culture dimorphs?
No!
- biosafety level 3 (same as anthrax)
- sporotrichosis: definitive diagnosis requires culture and demonstration of both phases*
What are the dimorphic fungi?
- Blastomyces dermatitidis
- Histoplasma capsulatum
- Coccidioides immitis
- Sporothrix schenckii
Which agents cause nasopharyngitis in horses?
Aspergillosis: gutteral pouch infection
**Conidiobolus coronatus: infects mucocutaneous sites = sinusitis, nasopharyngitis, upper respiratory disease in horses
What is the infectious particle of pythium?
Zoospore
What is the pathogenesis of pythium?
Zoospore contacts mucosa of GIT –> attach to damaged tissue, or invade mucosa and lymphatics
- OR: superficial injury in cattle, dogs, horses allows zoospore attachment, invasion and germination
= granulomatous inflammatory response
Pythium in the dog
Emaciation, vomiting, diarrhea, anorexia
- firm abdominal mass is palpated
- thickened stomach wall
Pythium in the horse
Granulomatous lesions, fistulated, ulcerated
- yellow-gray necrotic masses or cores of tissue (kunkers)
Pythium in calves
Multifocal areas of dermal thickening and ulceration on extremities
What is a kunker made out of?
Eosinophilic coagulum containing inflammatory cells with pyknotic nuclei
Overall histopathology of Pythium
Initially acute exudative inflammation
- characterized by predominant eosinophilia and early focal necrosis –> development of chronic inflammatory, and granulomatous reaction –> sequestration of necrotic areas
Which fungus gets in the eyes?
- Aspergillosis fumigatus (horse eye)
- ocular form of Blastomyces dermatitidis
What fungal agent causes brooder pneumonia in chickens?
Aspergillosis
Allylamines and non-azole ergosterol biosynthesis inhibitors
Lead to reduced ergosterol biosynthesis
- conceptually related to azole antifungal agents
- ex: terbinafine: inhibits squalene epoxidase
Antimetabolites
DNA substrate analog that leads to incorrect DNA synthesis
- flucytosine
- synergistic with azoles and amphotericin B
Azoles
Largest group, all inhibit synthesis of ergosterol by blocking the action of 14-alpha-demethylase
- ex: fluconazole
Glucan synthesis inhibitors
Inhibit glucan synthesis
- not used in vet med, too expensive
- inhibition of glucan produces significant antifungal effects
- ex: caspofungin
Polyenes
Potent, act by binding to fungal cell membrane using ergosterol as a target –> fungus leaks electrolytes
- ex: Amphotericin B (highly nephrotoxic!!)
Miscellaneous systemic agents
Griseofulvin: disrupts mitotic spindle
- used against dermatophytes
- comes as powder, mix in oil to help with absorption
Is Pythium a fungus?
Is more closely related to red algae and diatoms
- contains cellulose and beta-glucan in its cell wall as opposed to chitin, chitosan, alpha/beta glucans, and alpha mannans
- does NOT contain ergosterol!!
- still dealt with my mycologists due to morphology and staining characteristics
How is Pythium treated?
Typical antifungal/chemotherapeutic agents do not work
- surgical removal of affected tissue is treatment of choice (often not all affected tissue is removed)
- experimental bacterin used in horses and dogs at LSU, Australia
What fungus is a concern in piglets?
Candidia
- pseudomembrane on the tongue, esophagus, and stomach = vomiting and rapid wasting
