DERMATOLOGY - Fungal skin diseases 1 + 2 Flashcards Preview

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What are the 3 morphological groups of fungi?

- yeast (unicellular, budding)
- filamentous
- dimorphic (exist as yeast or filament depending on circumstances)


How do fungi reproduce?

vegetative growth and spores (not like bacterial endospores which are resistant. fungal spores are stable and viable in the dry state but are killed by disinfectants and boiling)


What are arthrospores?

= vegetative spores. formed by disarticulation of a septate hypha into separate cells. Frequently produced by dermatophytes (ringworm).


What are conidiospores and when are they found?

- formed externally by abstriction of teh conidiophore (simple or specialised) which arises directly from the mycelium or may be produced within a specialised fructification
- unicellular or multicellular
- some fungi species produce 2 types of conidia (different size and numbers of cells, micro and macro)


Outline dermatophyte production of micro and macroconidia

- microconidia and macroconidia only in culture
- dermatophytes exist only as hyphae or arthroconidia in hairy skin


How is the class of fungus determined?

sexual spores they produce and morphology


What are the 3 main ways fungi can cause disease?

- mycoses
- mycotoxicoses
- allergy


Define mycoses

fungi cause disease by invading and growing in tissue
- primary or opportunistic pathogens


Define mycotoxicosis

a fungi causes disease by producing toxigenic substances in themselves or in their growth substrates which when ingested cause disease


Define fungal allergy

a fungus that causes disease by producing sensitising substances that lead to hypersensitivity to fungal allergens


What do Histoplasma, Coccidioides and Dermatophytes have in common?

They are primary pathogens (capable of causing disease in healthy hosts)


What do Candida, Aspergillus and Zygomycetes have in common?

they are all opportunistic pathogens


How can mycoses be classified? 3

- superficial or cutaneous
- subcutaneous
- systemic
- endogenous versus exogenous


Define superficial/ cutaneous mycoses

- where skin and/or hair are involved
- ringworm
- resembles most bacterial and viral diseases (short incubation, sudden onset, CS decrease in severity over time, spontaneous healing)


Define subcutaneous mycoses

- SC tissues involved
- cutaneous manifestations may also occur (Sporotrichosis)
- Can spread through lymphatics


Define systemic mycoses

- internal organs affected (aspergillosis)
- SC and systemic mucoses tend to resemble aberaant bacterial diseases such as TB and leprosy (protracted incubation period, insidious onset, increasingly severe, death results)


Define endogenous mycoses

a few species of fungi which are normally harmless commensals of the body can cause illness when the host metabolism is in some way abnormal. Malassezia.


Define exogenous mycoses

caused by fungi from an external source. fungus must enter host, germinate and grow.


T/F: the parasitic state of fungi is of little or no significance in the LC of the fungus



What is the most important source of fungal infection?

airbone spores (e.g. conidiospores)


How can fungi cause damage to tissues?

- PENETRATION (tissues, nn, BV walls)
- THROMBI (zygomycetes have a predilection for BVs and penetrate the lumen)
- induce intense inflammatory and immunological reaction --> necrosis, sinus and fistula formation, dissolve bone (--> osteitis and osteomyelitis)


T/F: toxins are important to fungal pathology

False - although many fungi are known to produce exotoxins and enzymes but there is no conclusive evidence of toxin production within the body.


What are the 3 main mycoses caused by yeasts?

- Cryptococcosis
- Candidosis
- Malassezia pachydermatitis


What are the features of Cryptococcus neoformans

- spherical yeast
- polysaccharide capsule (only encapsulated yeast)
- bud on narrow base
- primary pulmonary infection, occasionally skin infection
- may spread by RES to CNS
- tip of nose (cats)
- worldwide distribution
- main source of infection = pigeon droppings. Also fruit, milk, soil.


How can Cryptococcosis be defined?

- exogenous mycosis
- acute, sub-acute or chronic
- no clearly defined clinical ppatern


Which systems does Cryptococcosis affect and how does this differ between species?

- SYSTEM: respiratory, CNS or systemic. Also possibly: cutaneous, skeletal, visceral and ocular.
CATTLE - Mastitis most important in cattle.
HORSE causes myxoma-like lesions of lung and lip.
DOGS/CATS show oral, pulmonary or cutaneous lesions and CNS. CATS - respiratory often accompanied by proliferative lesions of nasal cavity - tip of nose commonly too.


Which 3 species of Candida are responsible for candidosis?

C. albicans


What type of infection is candidosis usuallt?

C.albicans is normally an endogenous mycosis but occasionally exogenous infections may arise by ingestion or deposition. Mycoses caused by other Candida species are usually exogenous in origin.


How does C.albicans reproduce?



What type of fungus is Malassezia pachydermatis?

- lipophilic
- normal inhabitant of skin and mucosa of dogs, cats, carnuivores
- frequent opportunistic pathogen of dogs (otitis externa and dermatitis)

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