Fungal Pathogens Flashcards
What two forms can fungal pathogens take?
Mold and yeast
Are fungi prokaryotes or eukaryotes?
Eukaryotes (unlike bacteria which are prokaryotes)
What is a dimorphic fungus?
A fungus that can take two different morphological forms. At lower temperatures (<25℃) they take a mold form but at higher temperatures (35-37℃) they can take a yeast form.
Remember… mold likes da cold!
Are fungi aerobic or anaerobic?
Aerobic
At what temperature range do most fungi grow in?
20-30℃
What are the cell walls of fungi made of?
Chitin
What is the primary sterol used by fungal cells?
Ergosterol
What are the main targets for antifungal drugs?
Chitin and ergosterol
What are hyphae and mycelium?
Hyphae are individual filaments that make up the mycelium. Mycelium is a mat of branching hyphae.
True or False: Many fungal species are pathogenic
False, there are actually relatively few that are.
Fungal infections are _____________ in mammals and _____________ in ectotherms
Rare, common
Why do fungi rarely infect mammals?
Because most fungi grow best below the body temperature of endotherms (< 37°C)
What are the three steps of fungal pathogenesis?
- Tissue invasion (mycosis)
- Toxin production (mycotoxicosis)
- Hypersensitivity
When do fungal infections occur (two)?
- When an animal is in a state of immunosuppression (ex. Candida)
- Acquired from environment (ex. dimorphic fungi)
What are the three main phylums of fungi?
- Ascomycota (ex. Dermatophytes, Aspergillus, dimorphic fungi)
- Basidiomycota (ex. Cryptococcus)
- Zygomycota
Blastomycosis and histoplasmosis are examples of which type of mycosis?
Systemic mycosis
Dermatophytosis and candidiasis cause which type of mycosis?
Cutaneous mycosis
What disease form entails a fungal infection that spreads throughout the body and various organ systems?
Systemic mycosis
What is the infective agent that facilitates transmission of dermatophyte fungi between hosts?
Arthrospores. These tiny spores form from fragmented hyphae and can remain viable for 6-12 months (making it hard to decontaminate environment).
What does it mean that dermatophytes are geophilic, zoophilic, and anthrophilic?
Geophilic - can be free living in the soil
Zoophilic - have adapted to survive in animal host skin
Anthrophilic - adapted to survive in human host skin
How are dermatophyte infections transmitted?
- Close contact with other infected animals
- Direct contact with infected hair, fomites, or contaminated environment
- Fleas from infected animals
Dermatophytes utilize _______ for growth
Keratin
What age of animals are more susceptible to fungal infections?
Young and old animals
What organism causes more than 75% of dermatophyte infections?
Microsporum canis
How do some strains of Microsporum canis fluoresce under UV light?
They produce a tryptophan metabolite that glows apple-green along the whole length of the hair.
How should you collect samples from a dermatophyte infection?
Pluck hair from the edges of the lesions (fungi are more likely to be in the base of hair).
Can humans become infected with Cryptococcus spp. from their infected animal?
No. They can’t get it from the animal, only from the environment.
What fungal species causes avian crop thrush?
Candida albicans
What does Malassezia pachydermatis cause in cats and dogs?
Otitis externa and dermatitis
What most commonly causes systemic mycosis of cats?
Cryptococcus
What is the most common presentation with cats with cryptococcus?
Upper respiratory signs with sneezing and discharge and a swollen nasal bridge.
True or False: Cryptococcus is a dimorphic fungi
False. Don’t get this bad boy confused with Coccidioides immitis which is dimorphic!
In which species can aspergillosis occur?
All domestic species and humans.
____________________ is estimated to be responsible for 90-95% of Aspergillosis infections in animals
Aspergillus fumigatus
What condition occurs when young chickens inhale a large number of Aspergillus spores?
Brooder pneumonia
Which bacteria causes guttural pouch mycosis in horses? What does it do to the host?
It is caused by aspergillus species (ex. Aspergillus fumigatus). It is unilateral and has a 33% fatality rate because they bleed out when fungus invades prominent vasculature.
What do Aspergillus infections cause in cattle?
Mycotic abortion
What toxins does Aspergillus fumigatus produce? What do these lesions do to the host?
Osteolytic toxins. They will dissolve the turbinates and cribriform plate!
Name four highly infectious dimorphic fungi
- Blastomyces dermatitidis (level 3)
- Coccidioides immitis (level 3)
- Histoplasma capsulatum (level 3)
- Sporothrix schenckii (level 2)
What is the geographic distribution of Blastomyces, Coccidioides, and Histoplasma?
Blastomyces - Eastern USA and Canadian provinces that border the Great Lakes
Coccidioides - SW USA, Mexico, South America
Histoplasma - Eastern USA and Canadian provinces that border the Great Lakes
What is the pathogenesis of Blastomyces dermatitidis?
- Spores are inhaled
- In the lungs, spores convert to yeast form then go right to the blood
- Hematogenous spread
Systemic mycosis
Dogs are _______ times more susceptible to blastomyces than humans
10
What is the pathogenesis of Coccidioides immitis?
- Arthrospores are inhaled
- In lungs, spores develop into spherules
- Spherules mature and rupture, releasing endospores that spread via hematogenous route
Systemic mycosis
What is the pathogenesis of Histoplasma capsulatum?
- Spores are inhaled
- Macrophages in lung phagocytize spores and they turn to yeast form
- Yeast travels to lymph nodes, liver, spleen, then to the blood
- Hematogenous spread
Systemic mycosis
Infection with which fungus is colloquially known as ‘Valley fever’?
Coccidioides immitis
True or False: Infections from Sporothrix schenckii cannot spread to owners from infected animals
False, zoonosis is possible from contact with infected animal lesions or discharge (as well as scratches or bites).
True or False: It is best to diagnose Blastomyces dermatitidis, Coccidioides immitis, Histoplasma capsulatum, and Sporothrix schenckii through culture
False! Sending for culture poses a huge health risk to lab technicians! You should either do:
1. Cytology (aspirates, impression smears, etc.)
2. Serology (urine, serum, CSF)
3. Histopathology
If you need to culture, label your samples properly so technicians can take precautions.
What is a oomycete?
An aquatic organism that is not a true fungus.
Is Pythium insidiosum a fungus?
No, it is an oomycete. It is a zoospore that causes cutaneous infections in horses that can look like a fungal infection.
