Fungal Infections Flashcards
Why is human infection so rare by fungi
- 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
Examples of immunocompromising conditions that make a person more susceptible to fungal infections which are more rare, and more likely to disseminate
HIV, DM, pregnancy, leukaemia/lymphoma, chemotherapy and steroid use
Types of fungi
Moulds
Yeast
Dimorphic
Characteristics of mould (type of fungus)
Include how they grow, reproduce + named example
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
Characteristics of yeast infection
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
Characteristics of dimorphic fungi
Grow as yeasts (infectious) or moulds (saprophytic)
Eg coccidiodomycoses
Normally in the americas or some parts of west Africa
Non infections that present as clinical manifestations
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
Fungal infections can be classified into superficial or deep mycoses. What is the underlying pathology associated with superficial mycoses:
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
When are dematophytosis’s presented?
When no tissue is invaded but a host cellular response is elicited
Dermatophytes = environmental Filamentous fungi causing skin, hair and nail infections
Tinea corporis affects which part of the body
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)
Tinea pedis affects which part of the body and is caused by
Athletes foot
Caused by epidermophyton floccosum
Is anthropophillic in nature
Flaky itchy skin in between the toes
Tinea capitis affects what part of the body and cause
Ringworm of the scalp hair caused by microsporum canis that is zoonotic
Tinea cruris affects what part of the body and is caused by
The groin. Itching, stinging and burning rash
Caused by microsporum gypseum (zoonotic)
How to distinguish between ringworm and eczema
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
Tinea unguis
Affects nails
Caused by trichophyton rubrum
Anthropophillic
When and where do subcutaneous mycoses generally occur
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
Deep mycoses are most commonly located where and who is the most vulnerable
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
Black fungus and its significance
Deep infection caused by mucormycoses (mould) Rare but serious condition which is very difficult to treat
Life threatening
In general which people are most at risk of fungal opportunistic infections
Immunocompromised patients
Neutropenia, lymphopenia
Debilitated patients and those in the ICU, central lines and antibiotics
Clinical manifestations of invasive yeast, candida
Oesophagitis
Candidaemia which may seed to other organs
Endocarditis
Hepatosplenic candidiasis
How to differentiate between diagnosis of yeasts vs moulds
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
What is the antigen test for yeasts?
B glucan
What is the antigen test for moulds
Gallactomanan
Characteristics of a deep dimorphic coccidiodomycoses infection
Through inhalation of spores that results in respiratory symptoms
Maculopapular rash
Flu like symptoms
Chronic lung damage
Fibrosis
Which species of fungi does not respond well to any know anti-fungal drugs
Mucormycosis
Mechanism of action of amphotericin
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
Mechanism of action of Azoles and examples
Act by inhibiting the conversion of lanosterol to ergosterol that is needed in fungal cell wall biosynthesis
SE = liver damage
Candida is becoming resistant
Mechanism of action of echinocandins
Caspofungin inhibits glucan synthesis. Used to treat aspergillosis and Candidal infections
Resistant fungi= cryptococci and dermatophytes
