Fungi-animal Interactions

Question 1

What are the key ways fungi cause disease in animals?

Answer 1

Allergies = hypersensitivity to fungal antigens 
Mycotoxicoses = ingestion of fungal toxins 
Mycoses = fungus invading living tissue

Question 2

E.g. of mycotxicoses

Answer 2

Amanita muscaria has:

• Ibotenic acid = psychotropic effects
• muscarine = sweating and vomiting

Question 3

Different types of fungal infection of humans

Answer 3

Superficial
Cutaneous 
Subcutaneous 
Systemic-dimorphic 
Systemic - opportunistic

Question 4

Describe superficial human infection

Answer 4

In Skin/hair not living tissue

Question 5

Describe cutaneous human infection

Answer 5

In skin/hair

But causes inflammatory/allergic response

Question 6

Describe subcutaneous human infection

Answer 6

Chronic and localised infection in skin/subcutaneous tissue

Often saprotrophic fungi from soil/plant material

Question 7

Describe a systemic dimorphic human infection

Answer 7

Invades and develops in tissues of otherwise healthy host (no predisposition)
Infection normally pulmonary

Question 8

Describe system opportunistic human infection

Answer 8

In immunocompromised patients (e.g. AIDS, cancer)

Question 9

Describe bat white-nose syndrome

Answer 9

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

Question 10

Describe chytridiomycosis

Answer 10

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

Question 11

Why does bd drive species extinctions

Answer 11

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

Question 12

Describe oomycetes and e.g. of host

Answer 12

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

Question 13

What are the different methods of fungus arrival and entry?

Answer 13

• spores
• germination
• appressoria
• penetration

Question 14

Arrival and entry: spores

Answer 14

Needs to have sufficient contact time to germinate 
Stick to surface via:
- mucilaginous coats
- slime drops 
- host specific adhesive

Question 15

Arrival ad entry: germination

Answer 15

• need nutrients on cuticle (lipolysis activity probably occurs)
• must tolerate toxic compounds in cuticle
• non-pathogenic microbes may inhibit germination

Question 16

Arrival and entry: appressoria

Answer 16

Specialised fungal cell

Flattened hyphae with peg structure that uses turgor pressure to enter host cell

Question 17

Arrival and entry: penetration (sites and modes)

Answer 17

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

Question 18

What are the different methods of fungal establishment and exploitation

Answer 18

Host death
Tissue colonisation
Internal spread
Host defence

Question 19

Establishment and exploitation: host death

Answer 19

Can be caused by toxins e.g. destructions or toxic protease

Or chronic disruption of physiology following extensive mycelial development

Question 20

Establishment and exploitation: tissue colonisation

Answer 20

• 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

Question 21

Establishment and exploitation: internal spread

Answer 21

• 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

Question 22

Establishment and exploitation: host defence

Answer 22

Entry doesnt mean successful colonisation:

• phagocytosis (via haemocyanin)
• haemocytic = haemocytes encapsulate fungus
• humoral encapsulation = deposition of melanin protein complex on surface of fungus

Question 23

What are the different methods of exit and survival in fungi

Answer 23

Behavioural changes
Anchoring
Spores

Question 24

Exit and survival: behavioural changes

Answer 24

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

Question 25

Exit and survival: anchoring

Answer 25

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

Question 26

Exit and survival: spores

Answer 26

During active season: often ballistospores
Between seasons: resting spores
- only released when cadaver disintergrates
Some form pseudosclerotia

Question 27

What are the mechanisms of spore release to animals?

Answer 27

Mechanicals when insects pass over

Forcible discharged

Attraction of uninfected hosts

Question 28

Nematode trappers

Answer 28

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

Question 29

Affect of invertebrate grazing on mycelium

Answer 29

Reduced biomass
Compensatory growth
Altered interaction outcomes in fungal combat

Question 30

Invertebrate feeding on fruit body

Answer 30

Polyphagus = feed on many types of fruit bodies
Monophagus = specialised to one type of fungi fruitbody
- e.g. 50% polyporus feeders