Fungi-animal Interactions Flashcards
What are the key ways fungi cause disease in animals?
Allergies = hypersensitivity to fungal antigens Mycotoxicoses = ingestion of fungal toxins Mycoses = fungus invading living tissue
E.g. of mycotxicoses
Amanita muscaria has:
- Ibotenic acid = psychotropic effects
- muscarine = sweating and vomiting
Different types of fungal infection of humans
Superficial Cutaneous Subcutaneous Systemic-dimorphic Systemic - opportunistic
Describe superficial human infection
In Skin/hair not living tissue
Describe cutaneous human infection
In skin/hair
But causes inflammatory/allergic response
Describe subcutaneous human infection
Chronic and localised infection in skin/subcutaneous tissue
Often saprotrophic fungi from soil/plant material
Describe a systemic dimorphic human infection
Invades and develops in tissues of otherwise healthy host (no predisposition)
Infection normally pulmonary
Describe system opportunistic human infection
In immunocompromised patients (e.g. AIDS, cancer)
Describe bat white-nose syndrome
Bat = myotis lucifugus Was very coming now facing extinction Fungus erodes epidermal tissue so no fat reserves left in bat during hibernation Fungus optimum temp = 5-10C Hibernation = 2-14C
Describe chytridiomycosis
fungus - batrachochytrium dendrobatidis (Bd)
Climate change = alters amphibian habitat so fungus can spread and kill more = more extinction
Bd spread from South Africa due to global amphibian trade
- spread very fast, possible birds play a role?
Bd has zoospores that penetrate amphibian skin = skin thickening and therefore shedding
Electrolytes transport in skin to maintain homeostasis = disrupted so death
Why does bd drive species extinctions
Many strains of bd meeting in amphibian forms
Evolution of hyper infectious lineage of bd
Global trade = worldwide spread
Bd is broad host generalist with tolerant vector species = North American bullfrog
Describe oomycetes and e.g. of host
Oomycetes are water moulds
E.g. Cray fish
- infected fie in a couple weeks
-spread to Italy from N.America then across Europe
Spread to Uk as Swedish replaced crayfish with different species but turned out not resistant but carriers
What are the different methods of fungus arrival and entry?
- spores
- germination
- appressoria
- penetration
Arrival and entry: spores
Needs to have sufficient contact time to germinate Stick to surface via: - mucilaginous coats - slime drops - host specific adhesive
Arrival ad entry: germination
- need nutrients on cuticle (lipolysis activity probably occurs)
- must tolerate toxic compounds in cuticle
- non-pathogenic microbes may inhibit germination
Arrival and entry: appressoria
Specialised fungal cell
Flattened hyphae with peg structure that uses turgor pressure to enter host cell
Arrival and entry: penetration (sites and modes)
Sites are variable:
- directly through cuticle (thickness dependent)
- arthrodial membranes between joints and segments
- via sense organs and trachea
- via gut (withstand digestive enzymes)
- vulnerable ventral surface
Modes:
- dual enzymatic and mechanical
- successful only when reaches epidermis usually
What are the different methods of fungal establishment and exploitation
Host death
Tissue colonisation
Internal spread
Host defence
Establishment and exploitation: host death
Can be caused by toxins e.g. destructions or toxic protease
Or chronic disruption of physiology following extensive mycelial development
Establishment and exploitation: tissue colonisation
- haemocoel normally invaded first then spreads
- sometimes colonisation confined to certain tissues
E.g. entomophthora confined to abdomen of green apple bugs then posterior legs and wing muscles = can still drag on front. Releases ballistospores whilst it moves
Establishment and exploitation: internal spread
- Mycelial extension often localised to point of entry
- most produce dispersal structures to circulate haemolymph before germinating e.g. blastospores or hyphal fragments
- few colonise extensively as mycelium
Establishment and exploitation: host defence
Entry doesnt mean successful colonisation:
- phagocytosis (via haemocyanin)
- haemocytic = haemocytes encapsulate fungus
- humoral encapsulation = deposition of melanin protein complex on surface of fungus
What are the different methods of exit and survival in fungi
Behavioural changes
Anchoring
Spores
Exit and survival: behavioural changes
summit disease = infected invertebrates climb to higher point on plants
- interference with nervous system = increased O2 demand due to blocked spiracles? Or chemical interference with nervous system?
Clustering around infected individs
- release attractive volatiles
Insects become lethargic and crawl into cracks
- fungi produce resting spores rather than ballistospores
Exit and survival: anchoring
Pathogens of aerial insects anchor host = rigor mortis
- fungus doesnt want airborne host
- hyphae grow out of corpse into plant tissue
- stylets remain in plant
- can also clamp other insects
Exit and survival: spores
During active season: often ballistospores
Between seasons: resting spores
- only released when cadaver disintergrates
Some form pseudosclerotia
What are the mechanisms of spore release to animals?
Mechanicals when insects pass over
Forcible discharged
Attraction of uninfected hosts
Nematode trappers
Fungus creates constricting ring
- 3 cells
Nematode pulls head through, fungus takes up water quickly = contracts and nematode stuck
- then enters nematode
Can also kill nematodes via:
- adhesive rings
- adhesive knobs
- adhesive spores
- hooked conidia
Affect of invertebrate grazing on mycelium
Reduced biomass
Compensatory growth
Altered interaction outcomes in fungal combat
Invertebrate feeding on fruit body
Polyphagus = feed on many types of fruit bodies
Monophagus = specialised to one type of fungi fruitbody
- e.g. 50% polyporus feeders
