Fungi Flashcards
Sporotrichosis (causative agent, affected species, clinical syndrome)
Sporadic, chronic granulomtaous disease caused by the fungus sporothrix, which is ubiquitously present in the soil. Sporotrichosis has been reported in dogs, cats, horses, cows, camels, dolphins, goats, mules, birds, pigs, rats, armadillos, and humans. Zoonotic infection can occur from cats to humans and has been reported without evidence of trauma.Sporotrichosis may be grouped into three forms: lymphocutaneous, cutaneous, and disseminated. The lymphocutaneous form is the most common. Small, firm dermal to subcutaneous nodules, 1–3 cm in diameter, develop at the site of inoculation. As infection ascends along the lymphatic vessels, cording and new nodules develop. Lesions ulcerate and discharge a serohemorrhagic exudate.
In cats, lesions are most often present on the head, especially on the bridge of the nose and pinnae. Although systemic illness is not evident initially, chronic illness may result in fever, listlessness, and depression. Respiratory signs may be apparent.
The cutaneous form tends to remain localized to the site of inoculation, although lesions may be multicentric. Disseminated sporotrichosis is rare but potentially fatal and may develop with neglect of cutaneous and lymphocutaneous forms or if the patient is inappropriately treated with corticosteroids. Infection develops via hematogenous or tissue spread from the initial site of inoculation to the bone, lungs, liver, spleen, testes, GI tract, or CNS.
Itraconazole (10 mg/kg every 24 hours) is considered the treatment of choice for sporotrichosis. T
What fungus is pictured in this canine skin cytology?
Blastomyces (dimorphic, yeast in tissue) - The yeasts of B. dermatitidis and B. gilchristii are 8 to 15 μm in diameter, have a thick, refractile cell wall, and exhibit broad-based budding
What is the etiologic agent of ringworm, how is it diagnosed and and treated?
The dermatophyte Microsporum canis causes ringworm. Ringworm mainly affects cats and can be spread to humans and dogs. It can be diagnosed with direct cytologic hair examination, wood’s lamp examination, fungal culture, skin biopsy or PCR of lesions. Although it is technically self limiting, medical treatment reduces the length of disease. Treatment involves both topical antifungal (lime-sulfur dips) and systemic antifungal treatment (itraconazole) for the cat as well as environmental disinfection (accelerated hydrogen peroxide or OTC products labeled for Trichophyton spp). Treat until all lesions resolve and a fungal culture is negative (takes two weeks to get a negative culture). Depending on the severity of the infection, treatment is needed for 2 weeks - 2.5 months.
1) Topical: 2x per week whole-body lime sulfur dip (1:16 dilution). This is a leave-on product with residual activity after application. Can also be used for exposed animals. Chlorhex/miconazole shampoos for >3min are second line because they do not have residual activity. Spot treatment (once or twice daily) with a topical azole or terbinafine cream can be used for facial, ear or hard to reach lesions. Vaginal miconazole cream is safe for lesions near the eyes. Topical otic preparations containing miconazole, clotrimazole, or ketoconazole can be used daily to disinfect hairs within the ear.
2) Systemic therapy is necessary to eradict the infection at the hair follicle level and prevent re-seeding of the coat with spores. Tx of choice in cats is itraconazole (5–10 mg/kg PO q24h on alternating weekly cycles for 3 cycles).
3) Environmental. Mechanical cleaning and scrubbing with detergent are most important and often all that is needed. Remove organic pet debris (hair, etc) from clothes, carpet, hard sufaces, etc. In the initial clean, wash clothes 2 times, scrub carpet with antifungal shampoo, vaccuum/sweep/mop, and clean hard surfaces with OTC cleaning products (labeled against Trichophyton spp, ideally accelerated hydrogen peroxide based. Avoid bleach - it’s not a detergent. After that, keep pets off of soft surfaces (carpet, bed, etc). Discard disposable soft pet items (collar, bed, etc). Clean as if “company is coming” 1-2 times per week.
What fungal organism is seen in the blood smear (A) and lymph node aspirate (B)?
Histoplasma capsulatum (dimorphic, yeast is tissue). Small (2 to 4 μm) oval yeast with basophilic center surrounded by a clear halo, which results from shrinkage artifact. Seen extracellularly and intracellularly (usually within mononuclear phagocytes) on aspirates or impression smears of affected tissues (e.g., fine-needle aspirates of liver, spleen, lymph nodes, lung, bone mar- row), rectal scrapings, or cytospin preparations of lung wash specimens or body fluids (e.g., CSF, synovial fluid, ascites, or pleural effusion).
What fungal organism is seen in these cytology samples?
Cryptococcus (dimorphic, yeast in tissue) - extracellular, narrow-based budding yeast sometimes with extracellular vesicles.
What fungal organism is seen in the histopath sample (top) and cytology (bottom)?
Coccidioides spp (dimorphic, yeast in tissue) -Spherules may be visualized as large round, deeply basophilic, double-walled, slightly crinkled structures that range in diameter from 8 to 70 μm. Spherules are generally low in number, often associated with cellular aggregates, but often they are not evident or easily identified. Usually their internal structure is not easily discernable, but occasionally endospores are seen in association with ruptured spherules. The endospores are 2 to 5 μm in diameter, are surrounded by a thin, non-staining halo, and have small, round to oval, densely aggregated, eccentric nuclei. Endospores may be found extracellularly or within phagocytes.
What fungal organism is pictured in the cytology?
Sporothrix (dimorphic, yeast in tissue) - cigar-shaped to oval or round budding yeasts that are 3–5 μm by 5–9 μm in maximum length, with blue cyto- plasm and a single round nucleus surrounded by a nonstaining cell wall
What fungal organism is pictured in the lymph node aspirate (top) and renal histopath (bottom)?
Aspergillus - mold (saprophyte). Cytologic examination of blind or rhinoscopy-directed mucosal swabs, brush specimens of the nasal cavity, or nasal biopsies from dogs or cats with sino-nasal asper can reveal filamentous fungal hyphae and sometimes also conidia (spores). Hyphae stain well with Wright stain. They are septate and branch at 45-degree angles. Large numbers of degenerate neu- trophils, ciliated epithelial cells, and/or bacteria are also usually present
