Fungal Infections Flashcards
What are fungi?
They are eukaryote heterotrophs (obtain nutrition from their environment) that have cell walls.
What is the difference between yeasts and moulds?
Yeast:
-unicellular
-reproduce by budding
-some may produce hyphae and pseudohyphae
Moulds:
-multicellular
-reproduce using specialized spore structures
-produce hyphae
how do yeast reproduce by?
Budding
what are structures produced by yeast?
pseudohyphae
budding yeast
hyphae
What are pseudohyphae produced by and what do they look like?
Budding and elongation, and can resemble a string of sausages.
look at slide 4
What are hyphae produced by and what do they look like?
Apical extension from the protrusion out of a cell and these tend to have even and parallel sides at all times
look at slide 4
What kind of colonies does yeast produce?
Moist looking ones
slide 4
What kind of colonies do mould hyphae produce?
They’d form a colony on solid media that is round.
Sub-surface growth occurs & special spore structures may be on the surface
slide 5
How can you distinguish mould and yeast infections in tissue by microscopy
Compare the hyphae
Mould infection in skin. Hyphae are parallel sided and regularly septate (true hyphae)
Candida infected skin. Budding yeasts, pseudo hyphae and true hyphae present.
slide 6
Are any fungi commensal to humans?
Yeast:
Candida albicans- GI tract/oral
Other Candida species may be found in the GI
Malasezzia- skin
Moulds: No commensal moulds
What factors can predispose to candidiasis (risk factors)?
Age- infancy, elderly
Endocrine disorders
Defects in cell mediated immunity
Cancer
Drug addiction/Drug therapy- antibiotics, corticosteroids, immunosuppression
Surgery/IV catheters
What are the commonest Candida species?
Candida albicans, C. glabrata, C. tropicalis, C. parapsilosis, C. krusei
How do most Candida infections arise?
The species is commensal to GI tract, so usually infections arise from the endogenous flora but occasionally exogenous sources are implicated
e.g. hospital outbreaks and the commonest cause of these are C. albicans
What is the latest nosocomial (hospital acquired)problem?
Candida auris
Colonises readily, persists in environment, highly resistant to antifungals
Give some examples of oral manifestations of candidiasis.
slide 11
Acute pseudomembranous, detachable plaques
Chronic pseudomembranous, AIDS persistent
Chronic mucocutaneous candidiasis
What does oral candidiasis look like in children?
slide 12
Angular cheilitis may be present - an inflammatory skin process of variable etiology occurring at the labial commissure, the angle of the mouth
Oral candidiasis occurs in 4-8% infants, but if HIV+ 72-99%.
What are predisposing factors for intertrigo?
slide 13
intertrigo is the inflammation caused by the rubbing of one area of skin on another. caused by candida albicans
Obesity
Diabetes
Anything that increases your risk of skin folds because it’s brought on by occlusion, so the increase in moistness and colonisation of the skin eventually leads to infection
what Superficial infections are caused by Candida albicans?
interdigital
intertrigo
onychomycosis and paronychia -an infection of the skin around a fingernail or toenail.
Fingerweb / finger nail - occlusion and wetness, carriage of candida.
what is Candidiasis - nappy dermatitis?
Buttocks, perianal, groin.
Erythema, scaling, satellite lesions
1o or 2o invader? Association with faecal carriage of C. albicans
slide 14
What is chronic mucocutaneous candidiasis?
CMC may be inherited, associated with hypoparathyroidism or hypoadrenalism, hypothyroidism, or idiopathic.
Recurrent oral, skin, nail infection
Skin lesions on the face and scalp = candida Granuloma
slide 15
Can Candida cause systemic infection?
yes
Systemic means affecting the entire body, rather than a single organ or body part.
What do we mean by systemic infections?
Infection you find in the blood, lungs & internal organs, skin.
Endogenous source– resulting from predisposing factors
Exogenous source – outbreaks can occur in wards with severely debilitated hosts, uncommon
How does Candida albicans cause infection (1)?
- Ability to adapt to changes in environment- eg. pH. Sites include mouth, GI, vagina, skin
- Ability it adhere to different surfaces - Surface molecules bind to: iC3b, fibrinogen, fibronectin, laminin, epithelial cells , bacterial coaggregation with Streptococci and Fusobacterium species
- Production of destructive enzyme - Secreted aspartyl proteinases, phospholipases, hyaluronidase, degrade extracellular matrix proteins, etc enabling invasion
- Changes in cellular morphology -
Yeast, hyphae, pseudohyphae - Production of biofilms - Offers protection from environment, phagocytosis, and antifungals
- Evasion of host defence -
Block oxygen radical production and degranulation of PMN, kill monocytes. Cell wall components may have immunomodulatory effects, may stimulate cytokine release, may activate complement cascade - Toxin production - Candidalysin is a cytolytic peptide toxin secreted by C. albicans during hyphal invasion. Damages tissue and activates the immune response
What is the Candida pathogenicity?
Secretory aspartyl proteses (SAPs) have roles in adherence, invasion and development of disease
What is cryptococcosis?
A chronic, subacute to acute pulmonary infection resulting from inhalation of cryptococcus yeasts
On dissemination the yeast shows a predilection for the CNS & cryptococcal meningitis occurs.
What can systemic spread of cryptococcosis result in?
Skin lesions
Infection of bone and internal organs may also occur
how can Cryptococcosis be distributed?
Distribution - worldwide especially associated with bird droppings (eg. pidgeon)
what is the cause of Cryptococcosis
causative organism Cryptococcus neoformans
Is cryptococcosis particularly dangerous?
Only if you have HIV/AIDS or anything that makes your immune system extremely weak
How does cryptococcus exist?
Only in the yeast form, no hyphae produced
What is the major virulence factor of cryptococcus?
Capsule is protective, prevents phagocytosis
can synthesise Melanin which is immunomodulatory
how are moulds acquired by humans?
No commensal mould to the human body. Infections always exogenously acquired.
what are the two types of moulds
dermatophytes and aspergillus
What kind of infections do dermatophytes cause and what is the source?
Ringworm fungi
Common, superficial infection (affetcs outer layers)
Sources include human, animal & soil
What kind of infections do aspergillus cause and what is the source?
Uncommon, systemic (affect the blood) infection
Environmental source
Can often infect immunocompromised hosts
What factors predispose to mould infections?
- History of trauma to site of infection (cutaneous and subcutaneous)
2.Host immune status - can determine the extent of disease, duration, outcome
3.Underlying disease - may influence susceptibility to certain types of infection
4.Exposure to a source
5.Portal of entry
What do dermatophytes use as substrates?
Dermatophytes are a family of fungi that use keratin as a substrate
(so species infect hair, skin, nails).
Infections result from contact with a source
Affect healthy and immune compromise people
What is the commonest cause of skin & nail dermatophyte infection?
Trichophyton rubrum
What is tinea?
Medical term for ringworm (a clinical dermatophyte infection)
What is tinea capitis?
A fungal infection of the scalp characterised by red papules or spots at the opening of the hair follicle
What are the risk factors for tinea capitis?
Risk factors
age – most infections before puberty (mid teens). Uncommon in adults. Sebum production is inhibitory to fungal growth.
contact with infection - relevant history of exposure to source (human, animal, soil)
minor trauma to inoculate - scratching, hair dressing, barbers, sharing hats / towels etc
affects healthy hosts. Not more common in immune compromised hosts, but infections may be more florid.
What do clinical presentations of tinea capitis look like?
Often fine scaling, mild erythema, patchy alopecia
Hairs break at skin level: black-dot alopecia
slide 30
who is most likely to have
Dermatophyte scalp infection- tinea capitis?
Highly contagious among pre-pubescent children. Practice good hygiene and disinfect chairs and headrests.
What are the pathogenicity mechanisms for tinea?
- Adhesion (e.g by adhesins, enzymes)
- Invasion ( produce hyphae, complex process regulated by protein content and pH)
- Utilise keratin (breaking disulphide bridges)
- Manipulation of the immune response - cell wall mannans suppress lymphoproliferative activity
- Host adaptation (species associated with humans cause low grade chronic infections compared to animals)
look at slide 32 and 33
what is aspergillosis?
Causes systemic disease following inhalation of spores. Type of disease is determined by host status
what is the common form of aspergillosis?
Aspergillus fumigatus, A. flavus, A. nidulans, A. niger, A.terreus.
All are referred to as species complex as each comprises closely related organisms that are only distinguished genetically
What can aspergillosis cause?
- environmental moulds (decay in leaves + compost)
What are the different types of aspergillosis?
Allergic aspergillosis - temporary presence of aspergillus in respiratory tract, healthy host. Agricultural link, or exposure to large nos. 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
Cutaneous aspergillosis – primary infection due to skin damage (healthy or immune compromised).
what does A. flavus cause?
A. flavus causes aflatoxicosis due to ingestion of toxin produced in contaminated foods (peanuts), healthy host
