6. Fungal Pathogens (Tesse) Flashcards
Fungi are ___ pathogens
opportunistic
Why are fungal infections relatively rare in mammals
most fungi grow best below the body temperature of endotherms
What species are fungal infections common in
ectoderms (plants, insects, fish, reptiles, amphibians)
In mammals, fungi are typically considered either:
commensals (disease happens in states of immunosuppression) or environmentally acquired (disease follows exposure to large inoculum)
What are the three steps of fungal pathogenesis
- tissue invasion (ie mycosis)
- Toxin production (ie mycotoxicosis)
- hypersensitivity
what is an example of mycotoxicosis
aflatoxicosis, fusariotoxicosis, ergotism
What are the three types of fungal disease forms
- cutaneous mycoses
- subcutaneous mycoses
- systemic mycoses
What are the two veterinary dermatophytes?
Microsporum and Trichophyton
What do dermatophytes utilize for growth
keratin
what is the infective agent of dermatophytes
arthrospores, which facilliate transmission between hosts and can remain viable on shed hair and skin for at least 6-12 months
are arthrospores sexual or asexual
asexual
Where are dermatophytes found?
geophilic, zoophilic, anthropohilic
what does geophilic mean
free living saprophytes in the soil
what does zoophilic mean
adapted to survival in animal host skin
what does anthropophilic mean
adapted to survival in human host skin
Dermatophyte transmission
close contact, direct contact with fomites, fleas (mechanical vector)
what does infection by dermatophytes depend on
the hosts state - immunocompetence, skin conditions, nutritional state
What are the two dermatophyte species that affect cats and dogs
Microsporum canis, Trichophyton mentagrophytes
What are the two dermatophyte species that affect horses
Trichophyton equinum, Trichophyton mentagrophytes
what dermatophyte affects cattle and sheep
Trichophyton verrucosum
what dermatophyte affects pigs
Microsporum nanum
What species causes >75% of dermatophyte infections in cats and dogs
Microsporum canis
What is Microsporum canis infection more commonly known as
ringworm
Ringworm is characterized by ____ in dogs and ____ in cats
nodular dermatophytosis in dogs, dermatophytic mycetoma in cats
How should you collect dermatophyte samples
pluck hair from the edge of lesions ( fungi more likely to be in base of hair), scrape crusts, biopsy kerions and mycetomas. WEAR GLOVES
How can you visualize Microsporum canis in house?
- Woods UV lamps as a significant proportion is fluorescent
- trichograms/KOH wet mount to see arthrospores
-fungal culture (Gold standard)
-histo
when is treatment of dermatophyte infections strongly recommended?
for multianimal households or with immunocompromised humans
Where are Candida spp. commonly found
common in environment
What are the three main yeast and yeast like fungi
Candida, Malassezia, Cryptococcus
Where is Malassezia pachydermatis found
on the skin of mammals and birds, localized to areas with sebaceous glands
where is cryptococcus neoformans found
droppings of pigeons
where is cryptococcus gatti found
on trees
T/f: there is no zoonotic risk of cryptococcus infection via contact with an infected animal
true
Avian crop thrush is caused by
candida albicans
what species is particularly susceptible to oral candidiasis
young birds
t/f avian crop thrush typically only affects a small portion of a flock
false. its usually a large proportion
the clinical signs of avian crop thrush are
nonspecific
Candida albicans infection in birds causes gross lesions of>
raised, focal thickenings in mucosa of GIT (avian crop thrush)
What is the yeast like fungi that causes superficial infections in warm, moist anatomic sites
Malassezia pachydermatis - a normal flora of the ear canal of dogs and cats
Malassezia pachydermatis is a normal commensal to which body part of dogs and cats
ear canal
What is the most common systemic mycosis of cats
cryptococcosis
what is the incubation period of cryptococcosis in cats
2-13 months
How does cryptococcosis present in cats
upper resp signs - sneezing, ,polyp like masses on nose
hematogenous spread with possible CNS involvement
What is the best method for diagnosing yeast and yeast-like fungi
cytology (exudates, impression smears, tape preps, skin scrapings, biopsies)
What causes brooder pneumonia in young chickens
Aspergillosis
how are mature birds infected by aspergillus spp
inhalation of spore laden dust
Guttural pouch mycosis in horses is caused by ______
Aspergillus fumigatus
Mycotic abortion in cattle is caused by
Aspergillosis
Aspergillosis can present as either a ____ form or a _____ form in cats and dogs
nasal, disseminated
What species of aspergillus produces osteolytic toxins that can destroy nasal turbinates in cats and dogs
A.fumigatus
Dimorphic fungi undergo their yeast phase at ____ C and their mold phase at ____ c
Yeast phase at 35-37⁰C
Mold phase at ≤ 25⁰C
Where are dimorphic fungi found
in the environment
Blastomyces dermatitidis associated with
recent excavation
Coccidoides immitis associated with
dust storms
Histoplasma capsulatum associated with
bat/bird feces
Sporothrix schenckii associated with
traumatic inoculation
Why are animals important to human health relating to dimorphic fungi
they act as sentinels to disease
Where is Coccidioides immitis located
southwestern USA
blastomyces dermatitidis geographic location
eastern US and canada
Histoplasma capsulatum geographic location
US and Canada (mideastern)
Blastomyces dermatitidis pathogenesis
inhalation -> incubation period for 5-12 weeks -> seed in lungs -> hematogenous spread -> systemic signs
What are the clinical signs of Blastomyces dermatitidis
variable: low grade for days to weeks to months.
Respiratory (cough, dyspnea), lymphadenopathy, occular lesions, cutaneous lesions, lameness and neurologic signs. Also non-specific signs
Pathogenesis: Coccidioides immitis
dust storm leads to Arthroconidia disarticulation -> inhalation, spores land in bronchioles -> enlarge into spherules -> spherules mature-> mature spherules rupture ->inflammation and tissue damage
What is Coccidioides immitis infection known as
valley fever
What are the clinical signs of coccidioides immitis
nonspecific - fever, lethargy, inappetance, weightloss
What is the most important question to ask to determine if a dog may have valley fever
Travel history!
Histoplasma capsulatum disease pattern
disseminated
H. capsulatum in cats
vague and non-specific
H. capsulatum in dogs
nonspecific and diarrhea most common, due to predilection for intestines
in dogs, pulmonary histoplasmosis may be _____
self-limiting
what is recommended to prevent H.capsulatum dissemination in dogs?
Early therapy with antifungals
Sporothrix schenckii most commonly presents as ______ disease
lymphocutaneous disease
How does S. schenckii develop
damage to skin from contaminated plants
is Sporothrix zoonotic?
yes: contact from infected animal lesions or discharge
What should you NEVER do with pathogenic yeast or yeast-like fungi (think of DR Zachar’s resp path notes!!)
SEND FOR CULTURE! These are zoonotic pathogens of high risk to the humans doing the culturing.
Opportunistic fungal pathogens are inherently of ____ virulence and disease
low
what does infection by an opportunistic fungal pathogen depend on
diminished host defenses or traumatic inoculation
Pythium insidiosum geographic location
tropical and subtropical regions
is Pythium insidiosum a fungi
no -> its an aquatic oomycete that has fungal-like hyphae in tissues
what is pythiosis
lesions similar to mycetoma, disease similar to mucormycosis
what is a mycetoma
granulomatous nodules of subcutaneous tissue
what is mucormycosis
inhalation of spores or inoculation via trauma leading to mycetoma - like granulomas
what is phaeohyphomycosis
mycetoma-like masses
