Fungi

Question 1

Fungi- general characteristics

Answer 1

Uni (yeast) or multicellular organism
Aerobic eukaryotes
Defined nuclei
Cell walls of CHO and chitin- ergosterol in plasma membrane
Saprophytic or parasitic
Sexual and asexual repro
Asexual spores by mitosis- only found in clinical infection, no sexual reproduction in clinical infection.

Question 2

Fungi definition

Answer 2

Fungi: all yeasts, yeast-like organisms, dimorphics and moulds.
Yeasts: unicellular organisms that reproduce by budding- grow on skin, mucous surfaces and in the body- commensals, but can be pathogenic
Moulds: multicellular organisms that produce hyphae and mycelium (individual strains of hyphae) and spores (e.g. dermatophytes- hyphae grow in skin, hair and nails)
Dimorphic fungi: organisms that can produce both hyphae and yeast-like forms. Hyphae in environment (+spores) and yeasts in the infected host- geographically restricted.
-exhibit temperature dimorphism

Question 3

Fungi in veterinary medicine

Answer 3

Cutaneous and superficial mucous membranes- dermatophytes, malessezia, candida
Subcutaneous (rarest form)
Systemic: primary pathogens (histoplasma)- cause infection in healthy animals; opportunistic pathogens (aspergillus- disease causing in immunocompromised)
Toxins: mycotoxins
Allergy: to fungal spores

Question 4

Fungal benefits and pitfalls

Answer 4

Fungal products: ABX and mycotoxins (some are carcinogenic)

Fungal spoilage: animal foods, forages, animal products such as meat and hides

Question 5

Yeasts- general characteristics

Answer 5

single cells, reproduce vegetatively by budding
occasionally form pseudo mycelium (pseudo and true hyphae)- candida in particular do this
Sexual reproduction by forming ascospores within cell- only in nature, not in infected animal
Candida, malassezia, cryptococcus

Question 6

Candida- general characteristics

Answer 6

MUCH larger than bacteria, gram stain positive
yeasts, pseudohyphae, hyphae in tissue
chlamydospores- thick walled resting spores
grow at 37 degrees
form creamy white 2mm colonies in around 18 hours

Question 7

Candida albicans in animal disease

Answer 7

Cattle: mycotic abortion, rumenal infections, mastitis- may be superimposed after bacterial mastitis. ABX treatment will clear normal flora–> superimposed candida albicans infection
Pigs: dermatitis
Dogs: chronic enteritis and dermatitis, vaginitis/vulvitis in diabetes (yeast can use sugar present in tissues)
Birds: crop infection, enteritis
Man: mucosal and systemic infection

Question 8

Malassezia

Answer 8

skin commensals normally
bottle shaped
M. pachydermatis
Contain lipase and urease- break down lipid–>inflamm reaction
Otitis externa in dogs mainly
Dermatitis in all species- particularly dogs and cats

Question 9

Cryptococcus

Answer 9

C. neoformans, C. grubii, C. gatti
Inhalation of yeast cells in dust- pigeon feces
Opportunistic infections- defective cell mediated immunity, meningitis
Nasal cavity of cats with chronic rhinitis
Causes nasal, cutaneous, neural and ocular disease in cats.
Mucilagenous capsule- virulence factor

Question 10

Dermatophytes-microsporum, trichophyton sp.

Answer 10

Septate branching hyphal fungi
3 classes: anthrophilic (human-human), geophilic (enviro to animal/human), zoophilic (animal to human)
Digest keratin: hall mark- infect skin, hair and nails
Infectious spores=arthrospore
Form microconidia and macroconidia
Grow on sabouraud’s within 7-14 days, but up to 4 weeks.

Question 11

Ectothrix/endothrix

Answer 11

ectothrix- when you pluck hair, spores on the outside

endothrix- spores inside hair shaft

Question 12

Microsporum

Answer 12

ringworm in man and animals- looks like a cutenous parasitic infection.
Anthropophilic, zoophilic and geophili
Microconidia en thryse (along sides of hyphae)
Diagnosis by fluorescence under long wave UV light

Question 13

Microsporum canis

Answer 13

Ringowrm in cats and dogs– transmissible to man
Grows on hair with arthrospores- ectothrix
Micronidia relatively common
Macrocondiai elliptical with up to 14 divisions (canoe shaped)
Fluoresces
Colonies smooth white surface, yellow underside
Hair loss, skin inflammation, itchiness, scaly lesions

Question 14

Other microsporum species

Answer 14

M. gypseum- many macroconidia, dog, geophilic- associated with hedgehogs (doesn’t fluorescence)
M. nanum- pigs (not UK)- tropical disease

Question 15

Trichophyton

Answer 15

Zoophilic, ringworm in man and animals
club-shaped macroconidia 
-microconidia(en thryse and en grappe) 
spiral hyphae
no fluorescence of lesions

Question 16

T. verrucosum

Answer 16

ringworm in cattle transmissible to man
abundant chalmydospores- produced in culture only
-large spore ectothrix on hair
colonies slow growing- up to 8 weeks
embed themselves deep in agar

Question 17

Other species of tricophyton

Answer 17

T. mentagrophytes- dog, horse
-cigar shaped macroconidia, spiral hyphae
T. equinum- horse
T. galinae- fowl

Question 18

Aspergillus

Answer 18

not skin pathogens, respiratory, systemic opportunistic pathogens
Septate branching hyphae
sporing heads or conidia in O2
conidiophore and sterigmae
morphology of heads and culture which allows for diagnosis

Question 19

Aspergillus fumigatus

Answer 19

commonest in humans and animals
on food, fodder
sores infect young, non-immune or immunosuppresesed animals (also if you have A LOT of spores)
star shaped colonies
green-blude with sporing heads
need histopath evidence and culture to confirm

Question 20

Aspergillus disease

Answer 20

mainly respiratory infection- spore inhalation
pneumonia in newly hatched chicks
air sacculitis in birds- severe disease
guttural pouch mycosis in horses
nasal aspergillosis in dogs- particularly if on steroids
Mycotic abortions in cows- poor quality feed
Man- allergic diseases and severe infection in immunocompromised.

Question 21

Host defenses against aspergillus- lung

Answer 21

inactive conidia are inhalaed–> conidia lodge in lower respiratory tract–> conidia swell–> blocked by macrophages (in healthy animal hyphae prevented from forming)
If macs can’t block, conidia germinate into hyphae. Can be blocked by neutrophils. If not blocked, hyphae invade tissues. Can be blocked by neutrophils. If not blocked by neutrophils, hyphae invade BVs and disseminate.
Aspergillus have tropism for BVs–> like to go to brain.

Question 22

Dimorphic fungi

Answer 22

Geographically restricted (not in UK)
2 distinct forms: mould and yeast
Moulds in the environment, yeast in animal tissue (pathogenic)
Moulds produce spores–> spores inhaled or introduced into the skin
Species most associated: histoplasma capsulatum, blastomyces dermatitis, coccidioides immitis and sporothrix schenkii (subcut)

Question 23

Histoplasma capsulatum

Answer 23

Endemic in Mississippi and Ohio river valleys- man dogs and cats
Impaired CMI- will infect normal animals dependent on dose.
granulomas in lungs- a bit TB like
infection of macrophage- yeast cells gather together in macrophages (esp. alveolar macs)
Nitrogen within bird feces helps organism grow in soil. wind/dust helps aerosolize spores.

Question 24

Histoplasma capsulatum farcinimosum

Answer 24

epizootic lympangitis
spores enter through skin
ulcers over lymphatics and LNs
in horses mostly
rare fungal pathogen
india, africa, middle ast

Question 25

Zygomycetes

Answer 25

environmental fungi
broad hyphae, non-septate
asexual spores in a sporagnium
sexual spores oospores or zygospores
Mucor, Rhizopus, absidia, saprolengia
Infection uncommon in health animals
Immunodeficiency, steroids, ABX and diabetes
Abortion in cattle and rumentitis. 
No cross walls- hyphae v. broad compared to other hyphael fungi.

Easy to identify because fungus basically follows you off the plate- rapid growth within 24 hours.

Question 26

Mucor

Answer 26

Hyphae
grow fast in cultue
greyish-white aerial mycelium
pinhead fruiting heads full of spores
causes mycotic abortion, rumen ulcers, systemic mycosis in young or debilitated animals
Meat spoilage--> "whiskers" on bacon.

Question 27

Antifungal chemotherapy

Answer 27

Cell wall inhibitors, cell membrane inhibitors
direct membrane damage (punch holes and lyse membranes), disruption of microtubules and inhibition of mitosis (for dermatophyte infection), nucleic acid synthesis inhibitors (can’t use on it’s own d/t rapid resistance); inhibition of protein synthesis.

Animal cell membranes have cholesterol, yeast/fungal membranes have ergosterol.

Selective toxicity: antifungals target bits that are unique to fungi and not common to mammalian/animal cells.

Question 28

Mycotoxins

Answer 28

Secondary metabolites of fungal species in crops, pasture or stored feed. Low molecular weight, heat stable, non-antigenic, immunosuppressive, mutagenic, teratogenic, carcinogenic
Acute or chronic intoxication- Pencilium, Aspergillus, fusarium
Clinical dz: period of exposure, amount ingested

Question 29

Aflatoxin- difurancoumarins

Answer 29

Aspergillus species- Aflatoxicosis: absorption from GI tract, metabolized by liver to toxic product–> carcinogenic.

Question 30

Ergotism- ergopeptide alkaloids

Answer 30

claviceps purpurea- domestic animals and humans

seed heads of grasses and cereals. ergotamine and ergometrine–> affect nerves supplying arteriolar smooth muscles

Question 31

Mycotic oestrogenism- Zearalenone

Answer 31

potent non- steroidal estrogen produced by fusarium species. maize and other cereals.
repro problems in cattle and sheep.