Fungal Infections

Question 1

Why is human infection so rare by fungi

Answer 1

• saprophytes not well adapted to growth at 37 degrees
• enzymatic pathways work most efficiently at redox potentials in non living organisms
• poorly adapted to using human nutrients
• host defences are efficient at dealing with fungi
• slow growing
• don’t have a need to since are successful in environment

Question 2

Examples of immunocompromising conditions that make a person more susceptible to fungal infections which are more rare, and more likely to disseminate

Answer 2

HIV, DM, pregnancy, leukaemia/lymphoma, chemotherapy and steroid use

Question 3

Types of fungi

Answer 3

Moulds
Yeast
Dimorphic

Question 4

Characteristics of mould (type of fungus)
Include how they grow, reproduce + named example

Answer 4

Moulds grow by formation of hyphae which are filaments that the fungus uses to obtain nutrients

Mycelium = entangled mass of hyphae

Reproduce asexually via conidia (asexual spores), sexually via sexual spores or via their hyphae

Example: aspergillus

Question 5

Characteristics of yeast infection

Answer 5

Are single celled, reproduce by budding.
Some species form elongated hyphae called pseudo hyphae

In candida infections both true and pseudohyphae are seen

Other examples: cryptococcus neoformans

Question 6

Characteristics of dimorphic fungi

Answer 6

Grow as yeasts (infectious) or moulds (saprophytic)
Eg coccidiodomycoses

Normally in the americas or some parts of west Africa

Question 7

Non infections that present as clinical manifestations

Answer 7

Mycotoxins that result in ergotism. Caused by C. Purpurea. ( headache vomiting and gangrene of fingers and toes
Also may present as hypersensitivity reactions in the form of asthma and farmers lungs

Question 8

Fungal infections can be classified into superficial or deep mycoses. What is the underlying pathology associated with superficial mycoses:

Answer 8

No tissue is invaded and hence there is no cellular response from the host

Eg is tinea that is caused by a yeast that feeds on keratin

Resulting rash is small, pink and everywhere

Question 9

When are dematophytosis’s presented?

Answer 9

When no tissue is invaded but a host cellular response is elicited

Dermatophytes = environmental Filamentous fungi causing skin, hair and nail infections

Question 10

Tinea corporis affects which part of the body

Answer 10

Glabrous parts of the body (without hair)
Ringworm of the body
Itchy circular rash that is clear in the middle
Caused by trichopyhton rubrum
Is anthropophillic (requires humans for survival)

Question 11

Tinea pedis affects which part of the body and is caused by

Answer 11

Athletes foot
Caused by epidermophyton floccosum
Is anthropophillic in nature

Flaky itchy skin in between the toes

Question 12

Tinea capitis affects what part of the body and cause

Answer 12

Ringworm of the scalp hair caused by microsporum canis that is zoonotic

Question 13

Tinea cruris affects what part of the body and is caused by

Answer 13

The groin. Itching, stinging and burning rash
Caused by microsporum gypseum (zoonotic)

Question 14

How to distinguish between ringworm and eczema

Answer 14

Ringworm rash is not itchy and affects anywhere except the elbows and knees and is circular in appearance with raised borders whilst it is the opposite for eczema

Question 15

Tinea unguis

Answer 15

Affects nails
Caused by trichophyton rubrum
Anthropophillic

Question 16

When and where do subcutaneous mycoses generally occur

Answer 16

Followed on after traumatic inoculation and mostly seen in the tropics/sub tropics

Chronic infection can be locally invasive and can go deep enough to infect bones

Question 17

Deep mycoses are most commonly located where and who is the most vulnerable

Answer 17

Often after inhalation of spores that results in invasive pulmonary aspergillosis that may disseminate from the lung

Aspergillus fumigatus

If infects blood vessels may cause haemorrhage and infarction

Seen in those immunocompromised, severely neutropenic and lymphopenic.

Infections respond poorly to treatment + WBC remains low

Question 18

Black fungus and its significance

Answer 18

Deep infection caused by mucormycoses (mould) Rare but serious condition which is very difficult to treat

Life threatening

Question 19

In general which people are most at risk of fungal opportunistic infections

Answer 19

Immunocompromised patients
Neutropenia, lymphopenia
Debilitated patients and those in the ICU, central lines and antibiotics

Question 20

Clinical manifestations of invasive yeast, candida

Answer 20

Oesophagitis
Candidaemia which may seed to other organs
Endocarditis
Hepatosplenic candidiasis

Question 21

How to differentiate between diagnosis of yeasts vs moulds

Answer 21

Yeasts are seen in microscopy whilst moulds are seen in tissue
Moulds grow much slower on culture plates in comparison to yeasts
Moulds are not able to grow in blood culture and PCR cannot be used on them

Question 22

What is the antigen test for yeasts?

Answer 22

B glucan

Question 23

What is the antigen test for moulds

Answer 23

Gallactomanan

Question 24

Characteristics of a deep dimorphic coccidiodomycoses infection

Answer 24

Through inhalation of spores that results in respiratory symptoms
Maculopapular rash
Flu like symptoms
Chronic lung damage
Fibrosis

Question 25

Which species of fungi does not respond well to any know anti-fungal drugs

Answer 25

Mucormycosis

Question 26

Mechanism of action of amphotericin

Answer 26

Is a broad spectrum anti-fungal polyene which binds to ergosterol disrupting the fungal cell membrane

But has significant toxicity which results in renal damage and chills/fever during infusion
* lipid associated formulations much less toxic

Question 27

Mechanism of action of Azoles and examples

Answer 27

Act by inhibiting the conversion of lanosterol to ergosterol that is needed in fungal cell wall biosynthesis

SE = liver damage

Candida is becoming resistant

Question 28

Mechanism of action of echinocandins

Answer 28

Caspofungin inhibits glucan synthesis. Used to treat aspergillosis and Candidal infections

Resistant fungi= cryptococci and dermatophytes