Fugal Pathogenesis

Question 1

Define saprobes

Answer 1

Live on decaying organisms

Question 2

Diagnosis of primary fungal infections

Answer 2

Microscopically identified in clinical specimens taken from lesion

Question 3

Diagnosis of opportunistic fungi

Answer 3

• complicated because more ubiquitous
• found in contaminants in many cultures
• isolate lesions should be cultured repeatedly and samples at different times

Question 4

Effects of fungus colonisation

Answer 4

Mycotoxicosis

Hypersensitivity

Question 5

Characteristics of mycotoxicosis

Answer 5

Result of ingestion of fungi producing secondary toxic compounds

• ergot alkaloids
• psychotropic agents
• aflatoxins

Question 6

Characteristics of ergot alkaloids

Answer 6

• Inflammation, gangrene, conclusive symptoms (seizures), CNS effects (hallucinations, mania)
• prod. Alpha-adrenergic blockade (inhibition of adrenaline - vasoconstriction - low blood flow necrosis)
• stim. Smooth muscle contraction
• stim hypothalamus

Question 7

What are psyhotropic agents

Answer 7

Metabolites produced by fungi known as magical from ancient times - cause hallucinations

Question 8

Describe characteristics of hypersensitivity

Answer 8

Presence of antigenic spores that produce immunoglobulins sensitising lymphocytes.

• rhinitis
• bronchial asthma
• alveolitis
• Forms of atrophy

Question 9

How can fungal diseases be classified

Answer 9

Superficial mycoses - infections limited to outer layers of skin and hair
Cutaneous mycoses - extended deeper into dermis hair and nails
Systematic mycoses- originated primarily in king but can spread to many organs. Agents have unique morphology to survive respiratory tract

Question 10

4 types of superficial mycoses

Answer 10

• Pityriasis versicilor
• Tinea nigra
• Black piedra
• White piedra

Question 11

Characteristics of pityriasis versicilor

Answer 11

Caused by malessezia furfur, a lipophilic yeast organism

• requires fatty acids for growth
• found in normal flora, mostly on skin and subcutaneous glands
• Lesions of pityriasis are discrete hyper/hypo-pigmented areas that scale easily

Question 12

Diagnosis of pityriasis versicilor

Answer 12

Diagnosis is microscopic visualisation of characteristic “spaghetti and meatballs” in a potassium hydroxide treated specimen

Question 13

Characteristics of Tinea Nigra

Answer 13

Caused by Exophiala werneckii a dimorphic fungus producing pigment melanin.
Cells produce characteristic two-celled oval structures
- brown to black pigmentation on the palms and soles

Question 14

Diagnosis of Tinea Nigra

Answer 14

Visualisation if pigmented areas on skin and microscopy or yeast like cells and hyphae elements in KOH treated scrapings

Question 15

Characteristics of black piedra

Answer 15

Caused by piedraia hortae

• an organism that has to colonise hair to be in a perfect state
• hard black modules have a diagnostic value during examination of infected hair

Question 16

Characteristics of white piedra

Answer 16

• Yeast like trichosporon beigelii, organism growing in all lab media except those with cyclohexamide
• young cultures are white, older are yellowish
• dimorphism characteristics pronounce cultures

Question 17

Treatment of superficial mycoses

Answer 17

Usually no problems with treatment of properly and timely diagnosed
pityriasis and Tinea Nigra require removal of organism by external use of chemical to lyse keratin
- concoction of a multitude of sulphur derivatives

Question 18

True or false: cutaneous mycoses are limited to keratinised layers

Answer 18

True

Question 19

Characteristics of cutaneous mycoses

Answer 19

Cutaneous agents are called dermaphytes
3 types
- microsporum
- trychphyton
- epidermophyton 
Dermatophytes are keratinophillic fungi as it’s a substrate used to produce keratinises (virulence factors)

Question 20

Diagnoses of cutaneous mycoses

Answer 20

Examination of sample scrapings after alkali treatment to reveal spores

Question 21

Characteristics of subcutaneous mycoses

Answer 21

• initiate lesions, mostly after trauma allowing implantation of pathogen
• cause deep inflammation which can go on to a systematic response e.g. gangrene

Question 22

Characteristics of systemic mycoses

Answer 22

Caused by inherently virulent fungi including 5 species:

• Histoplasma capsulatum
• blastomyces dermatitidis
• Paracoccidioides brasiliensis
• coccidioides Immitis
• cryptococcosis neoformans

Question 23

What are the two phases of systemic pathogenic fungi

Answer 23

Saprobic phase 25 degrees

Parasitic phase 37 degrees

Question 24

True or false: primary site of infection of systematic mycoses is the liver

Answer 24

False, the lungs

Question 25

systematic fungal infection treatment

Answer 25

• mostly asymptomatic
• resistance to reinfection usually high
• sometimes infection spreads to other organs
• amphotericin B (intravenous) is always the best and universal option to treatment
• sometimes azole products can treat

Question 26

What is candidiasis

Answer 26

General term for symptoms caused by Candida yeast species

Question 27

Treatment of candidiasis

Answer 27

• typical treatment as for cutaneous infection

- for systemic infections - amphotericin B alone or combination with 5-flourocytosine; azole derivatives