Fungal infections Flashcards
3 classifications of fungi
yeasts
moulds
dimorphic
3 types of fungal infection
superficial- mucous membranes, keratinized tissues
subcutaneous
Systemic- opportunistic
most common cause of skin, nail and hair fungal infections
dermatophyte fungi e.g. Trichophyton (e.g.T. rubrum, T. interdigitale), Microsporum (e.g. M. audouinii) and Epidermophyton (e.g. E. floccosum)
how do dermatophytes cause disease
Dermatophytes digest keratin as a nutrient source
no living tissue invaded, only ‘dead’ keratinised stratum corneum involved however, fungus and metabolites induce allergic and inflammatory response in the host rash and inflammation
infections with dermatophytes are called what
tinea plus body site
diagnosis of dermatophyte infection
Skin scrapings or toe nail clippings – microscopy and culture
treatment of dermatophyte infection
Self-care measures:
Feet: keep feet cool and dry.Consider replacing footwear
General: Avoid scratching. Wash and avoid sharing towel
Medications:
Topical: Dermatophytes skin: Terbinafine 1% or Clotrimazole 1% cream, Miconazole 2% cream: 2 – 4 weeks. Pityriasis versicolor: ketoconazole or zinc pyrithione shampoo for Rx and prophylaxis. Fungal nail infection: amorolfine 5% nail lacquer – 6 months
Oral treatment: severe skin infections and nail infections
terbinafine or itraconazole –consider side effects and drug interactions
weekly fluconazole for pityriasis versicolor
RFs for mucosal candidiasis
recent antibiotics, HIV, malignancy, diabetes, immunosuppressive drugs eg steroid use (particularly inhaled steroids – oral candidiasis),
tx for mucosal candidiasis
Oral: treat with nystatin suspension, oral fluconazole if severe or in immunocompromised patients
Oesophageal: always requires systemic therapy e.g. PO fluconazole
define invasive candidiasis
Defined as isolation of Candida sp from an normally sterile site eg. Blood (candidaemia), intraabdominal tissue/fluid, abcess
examples of fungal causes of candidiasis
C. albicans
C. glabrata
C. tropicalis
Ix for candidiasis
Blood cultures – line and peripheral
Culture and microscopy of sterile site fluid/tissue and histology if feasible
Fungal biomarkers:1,3-β-D-glucan (BDG)
what should you always assess for in candidaemia cases
disseminated disease: listen to heart ang get an echo. Ophthalmoscopy to assess for candida endophthalmitis.
Tx for candidaemia
Treatment involves antifungal – initial empirical treatment with an echinocandin
removal of source of infection if possible
central line, urinary catheter, drainage of collections
Ix of aspergillosis
Culture – Broncho-alveolar lavage (BAL), tissue specimens
PCR – Broncho-alveolar lavage, tissue specimens
Histology tissue specimens
Galactomannan (GM) – can be done on BAL fluid and blood
- polysaccharide cell wall component released from aspergillus fungal hyphae during growth
- Detection of GM implies the presence of invasive disease
Used for screening in immunosuppressed patients and for diagnosis
Radiology – CT
Nodules
‘Halo’ sign – haemorrhage around nodule
Cavity
Tx for aspergillosis
voriconazole
can we culture PCP
nope
MOA of azole antifungals
Ergosterol synthesis inhibitors (block 14α-demethylase enzyme)
possible side effects of azole antifungals
Fluconazole: rash, raised aminotransferases, headache, seizures, Torsade de pointes/QT prolongation, hepatic failure, agranularcytosis
Vori-, itra- and posaconazole: as for fluconazole plus visual disturbance, ↓ glucose/K+/Na, neutropenia, thrombocytopenia
Voriconazole: photosensitivity and ↑ risk SCC with long term use
MOA of echinocandins- antifungal
Binds to and inhibits β(1,3) glucan synthase causing cell lysis
side effects of echinocandins
Hypokalaemia, D&V, rash, hepatotoxicity, seizures
MOA of polyenes: liposomal amphotericin
Bind to sterols (ergosterol preferentially) in the fungal cell membrane forming pores causing leakage of ions from cell
side effects of polyenes: liposomal amphotericin
Renal toxicity, hyponatremia, hypocalcaemia, hypomagnesaemia, hyperglycaemia, anaemia, hypotension, vasodilatation, flushing, infusion related reactions – fever/chills.
Uncommon: Anaphylaxis – administration of a test dose is advised prior to infusing 1st dose.
