Fungal Infections Flashcards
What are the 3 categories that fungal infections fall into?
- Superficial mycoses - confined to outer layers of epithelia
- subcutaneous mycoses- involve deeper layers of the skin & a different group of organisms
- systemic mycoses - penetrates the epithelia into the bloodstream & spreads through the body
Give an example of Superficial Mycoses
-Pityriasis
- caused by a lipophilic yeast which thrives on fatty acids found in sebum & affects pigment-producing cells
- results in a pink rash on pale skin & hypopigmentation in darker skin
Describe Ringworm
- superficial mycoses
- can occur throughout the body
- causes by keratin-degrading fungi
-they don’t invade underlying tissue - infections are usually self-limiting
- can be treated using topical/oral antifngal drugs
Give an example of Subcutaneous Mycoses
- Sporotrichosis / rose-gardener’s disease
- usually limited to the arms & legs
- caused by a dimorphic fungus found in soil
- infection usually follows abrasion of the skin
What are some examples of risk factors for opportunistic mycoses?
- HIV & AIDS
- chemotherapy
- transplant & subsequent immuno-suppressive treatment
- premature brith or extreme old age
What are the 2 main opportunistic mycoses ?
Candida & Aspergillus
Describe Candida
- species most frequently associated with human infection = Candida albicans
- harmless in healthy individuals
- can cause a wide range of infections of the skin & mucous membranes of mouth & vagina
- extremely rare circumstances candida can penetrate epithelia & enter blood causing life-threatening organ failure
How is candida treated ?
- usually treated with azoles & polyene drugs
- antifungal activity of azoles is due to inhibitor of ergosterol synthesis
Describe the diagnosis of candida
- blood sample is analysed using conventional culture methods
- can take up 48hrs for growth to be detected
-blood culture often fails to detect
Describe Aspergillosis
- filamentous fungi
- 20 species have been associated with human infections
- saprotrophic
- produce a vast number of spores (conidia)
Describe Invasive Aspergillosis
- patients at risk of acquiring this infection are generally profoundly neutropenic for prolonged periods of time
-reduced neutrophil counts & impaired alveolar macrophage function prevent the host from destroying conidia that are inhaled into alveoli - symptoms are non-specific
- mortality rate is very high
Describe Aspergilloma
- an infection that develops due to fungus colonising areas in the lung that have been damaged
- fungus proliferates & forms a large ball-like hyphal mass
- often asymptomatic
- usually treatable using antifungals
Describe Dematiaceous Fungi
- darkly pigmented because of presence of melanin in cell wall
- most common sites of infection are the sinuses
- repeated antibiotics to treat
What are some examples of endemic systemic mycoses ?
- blastomycosis
- histoplasmosis
What organisms typically cause endemic systemic mycoses infections?
- ascomycetes
- these are dimorphic and at about 25 degrees they take on a mycelial form, producing conidia
- at body temp 37 degrees they grow as yeast form
What does Dimorphic mean ?
having 2 forms of growth
How does the fungus become established once it was introduced at conidia ?
- fungus evades body’s immune system by changing its surface antigens, enabling it to become established
Define mycotoxicoses
- some fungal metabolites are toxic to humans = mycotoxins
- best common = aflatoxins & ergot alkaloids
Describe Aflatoxins
- produced by a range of aspergillum species
- frequently contaminate & produce toxins on crops & peanuts
- ingested aflatoxins are carcinogenic - liver cancer is the most common result of chronic exposure to the toxins
What is St. Anthony’s fire?
- common illness in the middle ages
- sufferers have hallucinations & experience burning sensations in limbs, leading to gangrene & death
- caused by Ergot which grows on rye grass
- contaminates rye flour used in bread
