38. subcutaneous mycoses & unusual fungi/fungal-like pathogens

sporothrix schenckii source

environmental → resides in soil, present on plant material

how does sporothrix grow in the environment vs in skin?

dimorphic

• grows as mold in vegetation & soil

• grows as a yeast in skin

sporothrix schenckii transmission

• spores are inoculated into the skin by minor trauma

• zoonotic → organism in draining fluid from lesions

sporotrichosis pathogenesis

• spores implanted in skin by puncture wound → germinate into yeast

• yeast multiply locally; resist killing by phagocytes

• yeast enter draining lymphatics → multiply in draining lymph node

• infection progresses and ascends along draining lymph nodes

• causes subcutaneous infection

sporothrix schenckii major hosts

• most severe in cats

• can infect dogs

• zoonotic → can infect people

sporotrichosis clinical signs (dogs/cats)

cats

• tends to cause severe, ulcerative lesions; dissemination

dogs

• ascending, nodular or ulcerative lesions

sporotrichosis diagnosis

• visualize cigar-shaped yeast in cytology or biopsy specimens

  • more useful in cats

• no available antigen test

• serology not helpful

• reference lab isolation of fungus by culture

  • grows as mold at <28°C; yeast at higher temps

• PCR in development

sporotrichosis treatment

• itraconazole = treatment of choice in cats

• can use oral potassium or sodium iodide in other species, including humans

• iodide toxicity common but reversible

immune response to sporothrix

• protective immunity not well understood

• experimental studies suggest cellular immunity important, but clinical disease can progress anyway

• antibodies formed but do not protect against disease

mycetoma (again)

• type of lesion caused by chronic infection of some bacterial/fungal agents

• implantation of microbe causes triad of signs:

  • swelling

  • draining sinus tracts

  • grains in exudate

what is an example of a fungal mycetoma?

• pseudallescheria boydii

• dematiaceous (pigmented) fungi cause pigmented grains

how are fungal mycetomas treated?

• excise lesion to reduce fungal burden

• often resistant to fluconazole, itraconazole

emerging (wildlife) fungal diseases source

carrier animals that shed fungus into environment (e.g. caves, burrows, water)

emerging (wildlife) fungal diseases transmission

fungal spores in environment are introduced on or into the skin to initiate infection

emerging (wildlife) fungal diseases pathogenesis

• spores germinate into hyphae and multiply in skin

• fungal growth and resulting inflammation damages integrity and physiologic function of skin

• likely unknown cofactors that influence severity of infection

pseudogymnoascus destructans is the causative agent of what disease?

white nose bat syndrome

white nose bat syndrome pathology

• white fuzzy growth on nose and wings

• causes physiologic imbalance

  • fat loss

  • blood chemistry changes

• bats awaken from torpor (hibernation) - fly around, lose weight, death

  • fungus grows below 20°C; disease primarily in winter

ophidiomyces causes what disease?

snake fungal disease

snake fungal disease clinical signs/pathology

• crusty scales

• subcutaneous nodules

• separation of outer skin

• opaque cloudiness of the eyes

• fungus usually restricted to epidermis — molting skin might clear infection

batrachochytrium dendrobatidis (chytrids) infect what animals?

• amphibians (ex. frogs, salamanders)

• invertebrates may serve as a reservoir

batrachochytrium dendrobatidis pathology

• colonizes skin of frogs and other amphibians

• disrupts physiologic function of skin → sloughing, death

what type of organism is pythium?

oomycete (intermediate between fungi and protozoa)

pythium & prototheca source

stagnant or pooled water

pythium & prototheca transmission

organism in the water is ingested or introduced into skin (pythium) or teat canal (prototheca)

pythiosis/protothecosis pathogenesis

• pythium:

  • motile zoospores invade tissue of animals in water

  • germinate into hyphae and multiply in skin

• prototheca:

  • multiplies as a round, yeast-like form

• both: organism growth and resulting inflammation damage tissue. infection is progressive with increasing tissue damage

pythiosis pathology

• necrotic lesions in limbs of horses and dogs

• necrotic enteritis in dogs and cats (ingested)

pythium geographic distribution

southeast US (ex. florida)

pythiosis diagnosis

• cytology

• PCR

• culture

pythiosis treatment

• drugs often ineffective

• surgically excise

what type of organism is prototheca? (+ growth on agar)

• alga that has lost its chlorophyll - NOT a fungus

• grows as multinucleated yeast-like organism on agar

protothecosis pathology

• dog: enterocolitis, abscesses

• cattle: environmental mastitis

  • no severe systemic signs

  • milk = watery with flakes and clots

  • progressive decrease in milk production

  • high SCC

• humans: progressive soft tissue infection

protothecosis treatment

• very resistant to drugs

• surgical excision

• milk infected cows last or cull