Fungal Infections

Question 1

What are fungi?

Answer 1

They are eukaryote heterotrophs (obtain nutrition from their environment) that have cell walls.

Question 2

What is the difference between yeasts and moulds?

Answer 2

Yeast:
-unicellular
-reproduce by budding
-some may produce hyphae and pseudohyphae

Moulds:
-multicellular
-reproduce using specialized spore structures
-produce hyphae

Question 3

how do yeast reproduce by?

Answer 3

Budding

Question 4

what are structures produced by yeast?

Answer 4

pseudohyphae
budding yeast
hyphae

Question 5

What are pseudohyphae produced by and what do they look like?

Answer 5

Budding and elongation, and can resemble a string of sausages.

look at slide 4

Question 6

What are hyphae produced by and what do they look like?

Answer 6

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

Question 7

What kind of colonies does yeast produce?

Answer 7

Moist looking ones
slide 4

Question 8

What kind of colonies do mould hyphae produce?

Answer 8

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

Question 9

How can you distinguish mould and yeast infections in tissue by microscopy

Answer 9

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

Question 10

Are any fungi commensal to humans?

Answer 10

Yeast:
Candida albicans- GI tract/oral
Other Candida species may be found in the GI
Malasezzia- skin

Moulds: No commensal moulds

Question 11

What factors can predispose to candidiasis (risk factors)?

Answer 11

Age- infancy, elderly
Endocrine disorders
Defects in cell mediated immunity
Cancer
Drug addiction/Drug therapy- antibiotics, corticosteroids, immunosuppression
Surgery/IV catheters

Question 12

What are the commonest Candida species?

Answer 12

Candida albicans, C. glabrata, C. tropicalis, C. parapsilosis, C. krusei

Question 13

How do most Candida infections arise?

Answer 13

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

Question 14

What is the latest nosocomial (hospital acquired)problem?

Answer 14

Candida auris

Colonises readily, persists in environment, highly resistant to antifungals

Question 15

Give some examples of oral manifestations of candidiasis.

Answer 15

slide 11

Acute pseudomembranous, detachable plaques

Chronic pseudomembranous, AIDS persistent

Chronic mucocutaneous candidiasis

Question 16

What does oral candidiasis look like in children?

Answer 16

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%.

Question 17

What are predisposing factors for intertrigo?

Answer 17

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

Question 18

what Superficial infections are caused by Candida albicans?

Answer 18

interdigital
intertrigo
onychomycosis and paronychia -an infection of the skin around a fingernail or toenail.

Fingerweb / finger nail - occlusion and wetness, carriage of candida.

Question 19

what is Candidiasis - nappy dermatitis?

Answer 19

Buttocks, perianal, groin.

Erythema, scaling, satellite lesions

1o or 2o invader? Association with faecal carriage of C. albicans

slide 14

Question 20

What is chronic mucocutaneous candidiasis?

Answer 20

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

Question 21

Can Candida cause systemic infection?

Answer 21

yes
Systemic means affecting the entire body, rather than a single organ or body part.

Question 22

What do we mean by systemic infections?

Answer 22

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

Question 23

How does Candida albicans cause infection (1)?

Answer 23

1. Ability to adapt to changes in environment- eg. pH. Sites include mouth, GI, vagina, skin
2. Ability it adhere to different surfaces - Surface molecules bind to: iC3b, fibrinogen, fibronectin, laminin, epithelial cells , bacterial coaggregation with Streptococci and Fusobacterium species
3. Production of destructive enzyme - Secreted aspartyl proteinases, phospholipases, hyaluronidase, degrade extracellular matrix proteins, etc enabling invasion
4. Changes in cellular morphology -
   Yeast, hyphae, pseudohyphae
5. Production of biofilms - Offers protection from environment, phagocytosis, and antifungals
6. 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
7. Toxin production - Candidalysin is a cytolytic peptide toxin secreted by C. albicans during hyphal invasion. Damages tissue and activates the immune response

Question 24

What is the Candida pathogenicity?

Answer 24

Secretory aspartyl proteses (SAPs) have roles in adherence, invasion and development of disease

Question 25

What is cryptococcosis?

Answer 25

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.

Question 26

What can systemic spread of cryptococcosis result in?

Answer 26

Skin lesions Infection of bone and internal organs may also occur

Question 27

how can Cryptococcosis be distributed?

Answer 27

Distribution - worldwide especially associated with bird droppings (eg. pidgeon)

Question 28

what is the cause of Cryptococcosis

Answer 28

causative organism Cryptococcus neoformans

Question 29

Is cryptococcosis particularly dangerous?

Answer 29

Only if you have HIV/AIDS or anything that makes your immune system extremely weak

Question 30

How does cryptococcus exist?

Answer 30

Only in the yeast form, no hyphae produced

Question 31

What is the major virulence factor of cryptococcus?

Answer 31

Capsule is protective, prevents phagocytosis can synthesise Melanin which is immunomodulatory

Question 32

how are moulds acquired by humans?

Answer 32

No commensal mould to the human body. Infections always exogenously acquired.

Question 33

what are the two types of moulds

Answer 33

dermatophytes and aspergillus

Question 34

What kind of infections do dermatophytes cause and what is the source?

Answer 34

Ringworm fungi Common, superficial infection (affetcs outer layers) Sources include human, animal & soil

Question 35

What kind of infections do aspergillus cause and what is the source?

Answer 35

Uncommon, systemic (affect the blood) infection Environmental source Can often infect immunocompromised hosts

Question 36

What factors predispose to mould infections?

Answer 36

1. 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

Question 37

What do dermatophytes use as substrates?

Answer 37

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

Question 38

What is the commonest cause of skin & nail dermatophyte infection?

Answer 38

Trichophyton rubrum

Question 39

What is tinea?

Answer 39

Medical term for ringworm (a clinical dermatophyte infection)

Question 40

What is tinea capitis?

Answer 40

A fungal infection of the scalp characterised by red papules or spots at the opening of the hair follicle

Question 41

What are the risk factors for tinea capitis?

Answer 41

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.

Question 42

What do clinical presentations of tinea capitis look like?

Answer 42

Often fine scaling, mild erythema, patchy alopecia Hairs break at skin level: black-dot alopecia slide 30

Question 43

who is most likely to have Dermatophyte scalp infection- tinea capitis?

Answer 43

Highly contagious among pre-pubescent children. Practice good hygiene and disinfect chairs and headrests.

Question 44

What are the pathogenicity mechanisms for tinea?

Answer 44

1. Adhesion (e.g by adhesins, enzymes) 2. Invasion ( produce hyphae, complex process regulated by protein content and pH) 3. Utilise keratin (breaking disulphide bridges) 4. Manipulation of the immune response - cell wall mannans suppress lymphoproliferative activity 5. Host adaptation (species associated with humans cause low grade chronic infections compared to animals) look at slide 32 and 33

Question 45

what is aspergillosis?

Answer 45

Causes systemic disease following inhalation of spores. Type of disease is determined by host status

Question 46

what is the common form of aspergillosis?

Answer 46

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

Question 47

What can aspergillosis cause?

Answer 47

- environmental moulds (decay in leaves + compost)

Question 48

What are the different types of aspergillosis?

Answer 48

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).

Question 49

what does A. flavus cause?

Answer 49

A. flavus causes aflatoxicosis due to ingestion of toxin produced in contaminated foods (peanuts), healthy host