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
- also implicated in causing dandruff
Describe Ringworm
- superficial mycoses
- can occur throughout the body
- causes by keratin-degrading fungi, the dermatophytes
-they don’t invade underlying tissue but may penetrate between cells where there is keratin - 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
Describe opportunistic mycoses
- human immune system is remarkably adept at protecting the body from fungal infection
-there is a wide range of clinical circumstances & this can result in certain species causing disease
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
