Fungal Infections Flashcards
What are fungi?
Eukaryotic
Obtain nutrients from environment
Can be environmental, commensal or pathogenic
What are the 2 types of fungi?
Yeast
Moulds
What are the main characteristics of yeasts? (3)
Unicellular
Budding (reproduction; copy themselves)
Some may produce hyphae and psuedohyphae
What are the main characteristics of moulds? (3)
Multicellular
Reproduce using specialised spore structures
Produce hyphae
What is pseudohyphae?
Elongated bud until it gets to a point where it can’t extend anymore, so it buds off again and it continues. Can look like string of sausages
What is ‘true’ hyphae?
Produced by apical extension from protrusion out of cell. Have even and parallel sides
What would mould look like if grown on a culture plate?
Round, sub-surface growth and special spore structures may be on the surface.
Hyphae in culture and on surface
When using a microscope, how could you differentiate between mould and yeast?
With mould it would look more regular due to presence of only true hyphae.
In yeast, you could see buds, pseudohyphae and true hyphae, so would much less regular
What are examples of commensal yeasts found in human?
Candida albicans (GI tract, oral)
Other candida species in GI
Malassezia (skin)
What are examples of commensal moulds found in the human body?
TRICK QUESTION
There are no commensal moulds found in humans
Name 5 factors that may predispose someone to candidiasis (8)
Age (infancy, elderly) Endocrine disorder Defects in cell mediated immunity Cancer Drug addiction Drug therapy - ABs, corticosteroids, immunosuppression Surgery IV catheters
Which yeast infection is most common in hospital outbreaks?
Candida albicans
Which type of candida is highly resistant to antifungals?
Candida auris
Outline the 3 oral manifestations of candidiasis
- Acute pseudomembranous detachable plaques
- Chronic pseudomembranous, AIDS persistent
- Chronic mucocutaneous candidiasis
Which viral infection greatly increases the chance of a candida infection?
HIV
In what parts of the body could you get superficial candida albicans infection?
Interdigital (finger web, finger nail)
Paronychia and onychomycosis
Intertrigo (e.g. breasts or groin area or obesity)
Usually due to occlusion and wetness
Which candidiasis affect babies?
Nappy dermatitis
What sites are mainly affected by systemic candidiasis?
Blood, lungs, skin, internal organs
Outline the 7 ways candida albicans causes infection
- Ability to adapt to changes in environment
- Ability to adhere to different surfaces
- Production of destructive enzymes (e.g. phospholipases)
- Changes in cellular morphology
- Production of biofilms (protects from environment, antifungals etc)
- Evasion of host defence mechanisms
- Toxin production (candidalysin damages tissue and activates the immune response)
Which destructive enzyme is produced by candida that have roles in adherence, invasion and development of disease?
Secretory aspartyl protease
What is cryptococcosis?
It is a chronic, subacute pulmonary infection resulting from inhalation of cryptococcus yeasts.
What is the causative organism of cryptococcosis?
Cryptococcus neoformans
What happens when cryptococcosis disseminates?
Often travels to the CNS and cryptococcal meningitis occurs
In blood - it can result in skin lesions and infection of bone and internal organs may occur
What are cryptococcal infections most associated with?
Bird droppings
Which type of cryptococcuscan cause infection of mostly immune competent hosts?
What is this most associated with?
Cryptococcus gattii
Associated with trees and soil - is endemic to certain regions (e.g Vancouver Island)
Does cryptococcus produce hyphae?
No - it only exists in yeast form
What major virulence factor does cryptococcus have?
It is able to form a capsule - this is protective and prevents phagocytosis.
What characterises a dermatophyte mould infection?
Common
Superficial infection
Healthy host
Sources include human, animal and soil
What characterises an Aspergillus mould infection?
Uncommon
Systemic infection
Environmental source
Immune compromised host or predisposing factors underlie disease
What factors predispose to mould infection? (5)
- History of trauma to site (cutaneous and subcutaneous)
- Host immune status: can determine extent of disease, duration, outcome
- Underlying disease: may influence susceptibility to certain types of infection
- exposure to a source
- Portal of entry
Ring worm is an example of what?
Dermatophyte mould
What do dermatophytes use as their main source of nutrients?
Keratin
What parts of the body can dermatophytes infect? (3)
Skin, nail, hair
Which mould family are the commonest cause of human mould infections?
Dermatophytes
Which dermatophyte is the commonest cause of skin and nail infections?
Trichophyton rubrum
What is the clinical name for dermatophyteinfection?
Tinea
How can you contract a dermatophyte infection?
Results from contact with a source (source can be from humans, animals or soils)
Do dermatophyte infections affect healthy people, immunocompromised people or both?
Both
What is the highest risk factor for Tinea capitis?
AGE
Most infections occur before puberty.
Uncommon in adults. This is because post-puberty scalps and skin tends to be greasier which is less favourable for fungal infections
The production of what is inhibitory to fungal growth?
Sebum production
How do you contract tinea capitis?
Exposed to a source - source can be human, animal or soil (most common is human to human).
Also require a minor trauma in order to inoculate (e.g. scratching, hair dressing, barbers, sharing hats etc)
Does tinea capitis affect healthy hosts, immune compromised or both?
Both - not more common in one than the other.
Although infection does tend to be more widespread in immune-compromised people
What is a kerion?
It is an inflammatory type of tinea capitis characterised by swelling and alopecia of the scalp
Outline the 5 pathogenicity mechanisms for tinea
- ADHERENCE: adhesins, enzymes, fibrillar projections on cell surface
- INVASION: phospholipases etc complex process regulated by protein content and pH
- UTILISE KERATIN: proteins in cornified layers of skin are rich in disulphide bridges. Dermatophytes use a sulphite pump to reduce disulphide bond in proteins that are then cleaved.
- MANIPULATION OF IMMUNE SYSTEM: cell wall mannans suppress lymphoproliferative activity
- HOST ADAPTATION: zoophilic species produce more protease than anthropophilic species
(Also tends to get passed around as people tend to get minor infections that they ignore or don’t realise as they are asymptomatic)
How does a person get an aspergillus infection?
They inhale spores and cause systemic disease
Which 2 aspergillus species are the most common causes for infection?
A. Fumigatus
A. Flavus
The type of disease caused by Aspergillus is determined by what?
Host status
Where might you find aspergillus?
In agriculture - like compost, soil, hay etc
Outline the 4 types of aspergillus infection
- Allergic aspergillus: temporary presence of aspergillus in respiratory tract, healthy host. Agricultural link, or exposure to large numbers of spores.
- Aspergilloma: colonisation of pre-existing cavities, fungal ball in lung, predisposing factors for lung cavitation but may otherwise be healthy
- Invasive aspergillosis: pulmonary focus, dissemination possible, immune compromised host
- Systemic aspergillosis: lungs, brain, other organs, immune compromised host.
