mycology part 1

Question 1

types of fungal infections

Answer 1

cutaneous mycoses –> dermatophytes

subcutaneous mycoses

systemic mycoses
- opportunists
- primary pathogens

Question 2

establishment of fungal infection

Answer 2

requires reduced host resistance

Question 3

decreased LOCAL resistance

Answer 3

loss of normal cutaneous barriers
- trauma or prolonged moisture

loss of normal bacterial flora
- prolonged antibiotic use

local immunosuppression
- topical corticosteroid use

Question 4

decreased SYSTEMIC resistance

Answer 4

malnutrition

immunosuppression
- genetic immunodeficiency (CID)
- chemotherapy
- immunosuppressive infection (FeLV)

Question 5

spread of infection

Answer 5

most fungi are aerobes

most optimally grow at 25º-30ºC so don’t grow well in the body
- some exceptions
-aspergillus fumigatus - optimal growth up to 45ºC (brooder pneumonia
- pathogens causing systemic mycosis grow well at 35ºC - many are dimorphic fungi

Question 6

cutaneous mycoses - geophilic dermatophytes

Answer 6

geophilic dermatophytes - species that grow and replicate in the soil, esp. with hair

cause sporadic disease in animals

are poorly transmitted between animals

ex. microsporum gypseum aka nannizzia gypsea
- second most common dermatophyte infecting dogs

Question 7

cutaneous mycoses - zoophilic dermatophytes

Answer 7

zoophilic dermatophytes- are obligate parasites on animals - do NOT multiply or persist in soil

spread rapidly among animals - unique among fungi!!!

are zoonotic - but generally do not cause outbreaks among humans

example: microsporum canis in cats

Question 8

cutaneous mycoses - anthropophilic dermatophytes

Answer 8

anthropophilic dermatophytes
- species of dermatophytes that are obligate parasites predominately found on humans

Question 9

microsporum and trichophyton

Answer 9

phylum Ascomycota –> the “sac fungi”

have septate hyphae

have sexual and asexual life cycles

sexual produce conidia

asexual produce asci (singular ascus) - sac like structure enclosing spores

Question 10

dermatophytes: establishment of infection

Answer 10

arthroconidia enter damaged skin
- abrasions can be microscopic

arthroconidia germinate to hyphae in stratum corneum
- growth in stratum corneum and adjacent to hair follicles
- masses of hypae and arthroconidia

periodic acid-schiff stain (PAS)
- aids diagnosis via histopathology

Question 11

dermatophyte- host relationships - microsporum canis

Answer 11

natural host is the cat (despite the name) - zoophilic

subclinical infection is common

accounts for 90% of cat dermatophytosis

accounts for 40-70% of dog infections

Question 12

microsporum canis

Answer 12

sporadically zoonotic

~15% of human ringworm is zoonotic

children are particularly susceptible

warn clients of zoonotic potential when you diagnose M. canis infection!

Question 13

microsporum periscolor

Answer 13

a zoophilic and geophilic fungi

primarily affects dogs
- rodent hunters
- cats, rabbits, rodents

epidermatophyte
- does not infect hair shafts

Question 14

microsporum gypseum

Answer 14

the #1 dermatophyte of horses in the south
- trichophyton equinum is #1 everywhere else

poorly zoonotic\

Question 15

more zoophilic dermatophytes

Answer 15

trichophyton - a common genus in agricultural animals
- T. equinum and T. mentagrophutes are most common in horses
- T. verrucosum - most common in cattle

microsporum nanum - common in pigs
- porcine ringworm

Question 16

Trichophyton mentagrophytes

Answer 16

a common dermatophyte of dogs

reservoir in wild rodents

Question 16

diagnosing dermatophytes

Answer 16

clinical exam
- woods lamp
- experience

laboratory
- culture - dermatophyte test medium - sabouraud’s agar
- potassium hydroxide (KOH) preps of hair crusts

Question 17

wood’s lamp diagnosis

Answer 17

UV light (320-400 nm) - a black light!
- tryptophan metabolites fluoresce (glow)

M. Canis glows 30-50% of the time

Trichophyton spp. almost never do

Question 18

woods lamps diagnosis

Answer 18

false positives CAN occur
- certain ointments
- dead skin
- pseudemonas spp.

false negatives can too
-nonfluorescing strains
- cold wood’s lamp

Question 19

KOH preperations

Answer 19

KOH dissolves skin cells and debris, leaving hyphae behind

Question 20

Growth of fungi on media

Answer 20

Dermatophyte test medium (DMT)
- presumptive diagnosis
- false positives are possible

sabaraud’s medium

Question 21

using a derm-duet

Answer 21

a combination plate of DTM and saboraud’s

DTM will turn red quickly with dermatophytes (>7 days)
- will occur very slowly with saprophytes

incubate in the dark and examine daily

sporulation will occur on Saboraud’s faster which aids in ID

Question 22

Sampling

Answer 22

collect hair and desquamating scales

Question 23

Dermatophyte treatment - topical

Answer 23

large animal
- mostly self limiting
- increase exposure to sunlight

small animals - topical tx is key
- need to treat whole animal - spot therapy leads to chronic subclinical carriage

cleaning tack, etc
- lime-suilfer
- 10% bleach

Question 23

systemic treatment

Answer 23

oral azoles - inhibit ergosterol (a component of fungal cell membranes) synthesis - ketoconazole - itraconazole - fluconazole Griseofulvin - disrupts microtubule assembly - great penetration of keratin! - teratogenic - losing popularity

Question 23

malassezia spp.

Answer 23

phylum Basidiomycota - M. pachydermatitis Most significant in veterinary medicine - normal inhabitant of mucocutaneous junctions, ears infections occur due to underlying problem - anatomic defect (moist, ceruminous ears) - sebaceous material - allergy !! (atopic disease) - antibiotic therapy

Question 23

M. pachydermatis

Answer 23

typically diagnosed clinically or cytologically don't need to routinely culture

Question 23

M. pachydermatis

Answer 23

very rarely zoonotic neonatal fungemia has been reported in NICUs - associated with parenteral feeding of lipid emulsions to neonates also sometimes reported in severely immunocompromised adults

Question 23

subcutaneous mycoses

Answer 23

sporotichosis - sporothrix schenkii Oomycosis -pythium insidiosum Zygomycosis - mucor - basidiobolus

Question 23

Sporotrichosis host and other info

Answer 23

Sporotrhix schenkii - thermal dimorphism - free living mold - thriving in sphagnum may cause disease in - horses - dogs - cats - people - ROSE PICKERS DISEASE

Question 23

sporotrichosis entry, spread, response

Answer 23

entry - open wounds/ broken skin - common to head, neck, extremities spread - turns into yeast form in SQ (thermal dimorphism) - spreads to lymphatics - not typically spread to organs - masses can rupture/ulcerate host response - cell-mediated (macrophage activation)

Question 24

sporotrichosis diagnosis

Answer 24

consider in non healing wounds other differentials: - neoplasia - rapidly growing mycobacteria nocardia - in dogs: non-responsive (to antibiotics) deep pyoderma Is zoonotic - be careful with discharge from wounds cytology histopathology typically will see intralesional yeast - cigar bodies

Question 25

"Hyperendemic" sporotrichosis in S. America

Answer 25

>5000 cat associated human cases since the 1990's cases also reported in the UK from imported cats sporothrix brasiliensis - more virulent than S. schenkii

Question 26

pythium insidiosum geographic distribution

Answer 26

tends to be found tropical/subtropical regions with stagnant water

Question 27

P. insidiosum - an oomycete (pseudofungus)

Answer 27

most often effects - horses - dogs - humans also known as - swamp cancer - leeches enters via open wound or ingestion causes chronic, non healing granulomas

Question 28

treatment of subcutaneous mycoses

Answer 28

local excision amputation systemic antifungals - amphotericin B - ketoconazole - Na or K iodide Immunotherapy for pythiosis - humans, horses, dogs - some evidence that it helps in humans

Question 29

zygomycosis - basidiobolus

Answer 29

associated with dung of amphibians, reptiles, and tropical bats causes deep cutaneous infections in - dogs - horses - humans

Question 30

zygomycosis - Mucor and Rhizopus

Answer 30

Mucormycosis is the most common form of zygomyhcosis - terms used somewhat interchangeablyh only seen in sevelry immunocompromised patients common contaminants of fungal cultures - its presence VERY RARELY signifies DZ - must have in conjunction with histopatholy