Basic mycology + fungi as infectious agents Flashcards
What are eukaryotes?
Organisms whose cells have a nucleus enclosed within a nuclear envelope
What does heterotrophic mean?
Means they are consumers
What are fungi?
Eukaryotic, heterotrophic
Fungi can be saphrophytes - what does this mean?
They live off of decaying matter
Fungi can be symbionts - what does this mean?
They can live in symbiosis with other living things
Fungi can be pathogens - what does this mean?
An agent or organism that can produce disease.
An infectious agent - a germ
What are the two components of fungi?
1) Fruiting body
2) Mycelium = a network of branched, tubular filaments
What are the different forms of fungi?
1) Yeasts = single celled fungi
2) Filamentous = long strands
3) Dimorphic = yeasts or moulds
Describe fungi
- Decomposers
- Cell wall made of chitin
- Has a nucleus
- Slightly acidic in soil
- Undergoes asexual or sexual reproduction - Gain energy from dead matter
- Multicellular (apart from yeast)
How do fungi cause disease?
Fungal diseases include both the invasion of tissues by fungi and the effects on organs of fungal positions.
What are the three different ways fungi can cause disease?
1) Mycoses = invasion of tissue
2) Mycotoxicosis = ingestion of toxins
3) Fungal allergy = hypersensitivity to fungal antigens
Mycoses can be endogenous or exogenous - what do these terms mean?
Endogenous = natural commensals may become opportunistic pathogens
Exogenous = soil, decaying plant material, water or other animal
Mycoses can have different sites of infection - what are these and give examples.
Superficial = dermatomycosis
Subcutaneous = sporotricosis
Systemic = cryptococcosis
What is yeast - malasezzia pachydermatis and what can it cause?
Commensal
Causes: mild skin disease, allergies, budding on a broad base, implicated in otitis externa in dogs
What is aspergillosis?
Inhalation of fungal spores
What colour do fungi stain in a PAS stain?
Pink
What colour do fungi stain in an H&E stain?
Purple
What can sometimes be seen in an H&E stain of fungi?
Necrosis, granulomas containing yeast-like bodies
What is yeast candida albicans?
- Commensal of nasopharynx, GIT and external genitalia
- Opportunistic
- Budding on a narrow base
What is yeast Cryptococcus neoformans
- Encapsulated yeast
- Infection from environment
- Found in bird droppings
- Primary pulmonary infection (respiratory) may spread to CNS
- Sporadic
- Spherical cells, budding on a narrow base
What is filamentous fungi - saprolegniasis
- Freshwater fish
- Usually secondary infection
- Cold water
- Cotton wool like appearance on skin and gills.
What is filamentous fungi - mucormycosis
- Damages the rumen wall. If grass-fed it increases acid and there is a reduction in pH = ruminal acidosis
- Leads to fungal invasion and progresses to granulomatous rumenitis
- Also found in calves given antibiotics due to distribution in normal flora
- Can be spread via the portal vein to liver
Filamentous fungi - mucromycosis can be either… or ….
Bread mould
Sporangiospores
What does filamentous fungi cause?
- Mycotic abortion
- Guttural pouch mycosis
- Avian aspergillosis
- Pulmonary aspergillosis
- Canine nasal aspergillosis
What structural feature does FF aspergillosis have?
Sporing heads
Separating mycelium
What is Filamentous fungi dermatophytes?
The fungi that cause ringworm - dermatomycosis
Affects skin in most species
What are the 3 types of dermatophytes?
1) Microsporum sp
2) Trichophyton sp
3) Epidermophyton sp
What two types of fungi are associated with dermatophytes?
1) Keratinophilic fungi = breakdown hair and colonise keratinous substrates, degrading them into components of low molecular weight
2) Contagious fungi
What are the dermatomycosis epidemiological groups?
- Anthropophilic
- Zoophilic
- Geophilic
What hosts do anthropophilic prefer?
Preferring human hosts over other animal
What hosts preferences do zoophilic have?
Preference to animal host
What host preference do geophilic have?
Preferring soil host
What is dermatomycosis clinical appearance?
Crusty grey lesions on the head and neck
Seen in calves, dogs, horses, cats, poultry
How do you do a wet preparation of fungi for microscopy?
Scrape or smear and add KOH or paraffin oil
What two mediums can be used for cultures?
Sabouraud’s medium
Malt extract agar
How long do you leave filamentous to culture for and at what temperature?
27 degrees C
7-10 days
How long do you leave yeast to culture for and at what temperature?
37 degrees C
24-36 hours
What pH do you culture at?
Low pH
What antibodies do we use on cultures?
Chloramphenicol
Cyclohexamide
What is serology used for?
Detecting the antibody in animal serum from a clotted blood sample
What tests can be used in serology?
ELISA
CFT
Immunoprecipitation
What is CFT used for?
CFT = complement fixation test. Used for histoplasmoids, blastomycosis, aspergillosis and coocidioidomycosis.
Antibodies are present in the serum, when mixed with corresponding antigens, they will bind. Then use an assay system.
If antibody present, no fungi as all bound
If antibody not present in blood, there is fungi
How can we diagnose dermatomycosis?
History and clinical signs
Use woods lamp
Microscopy
Culture
Sample - pluck hair or scrap
How does a dermatomycosis woods lamp work?
- Uses long wave UV light which reflects off skin
- If present there will be an apple green fluorescence on hair and skin
How do you culture dermatomycosis
- Sabourauds agar
- Use antibiotics to prevent bacteria invasion
- Different strains look different
- Usually at 27 degrees C
What does PAS stand for?
Periodic acid-schiff stain
How does dermatomycosis stain?
PAS stain on fixed tissue
Fungi will stain purple/red
What animals does dermatomycosis affect?
Dogs
Cats etc
What is dermatomycosis infection associated with?
- Young animals
- Grooming equipment
- Minor trauma
- Mixing with other/ wild animals
How can dermatomycosis be controlled?
Disinfectants
Shampoos
Avoid mixing infected
How can dermatomycosis be treated?
1) Griseofulvin = oral
2) Azole antifungals = oral or topical
How does ringworm develop and spread (pathogenesis)
- Arthrospores germinate
- Infective hyphae grow into the skin and down into the hair follicle
- Hyphae grow downwards and penetrate within the hair shaft
- Arthrospores form arond the now brittle hair shaft as the hyphae age
- The hair breaks and falls away - infecting the environment.
- Hyphae will not penetrate living tissue
In dermatomycosis what may a secondary bacterial infection cause?
May cause permanent damage to the follicle and dermis
