Clinical Mycology Flashcards
Classification of diseases
Superficial
- Skin: dermatophytosis, tinea versicolor
- mucous membrane: candidiasis
Subcutaneous
- Dermis: eumycetoma, sporotrichosis
Invasive
- blood stream: candidaemia
- pulmonary: aspergillis, pneumocystis
- CNS: cryptococcal meningitis
- sinuses: aspergillus, zygomycetes
Superficial infections: Dermatophytosis - organisms, transmission, characteristics of infection, signs and symptoms
Trichophyton, Epidermophyton and Microsporum species
Transmission: direct (scratching) or indirect contact; minor trauma with inoculation
Keratinophilic fungi (keratinase to digest keratin layer and infect) --> rarely invades deeper into tissues or blood as they are inhibited by human sebum
Affect skin, hair, nail
–> tinea, ringworm, athelete’s foot
Signs and symptoms:
- itchiness
- multiple lesions (self inoculation)
- dry and scaling
- wet, macerated with exudates
- persists for wks or months
Dermatophytosis: specific manifestations
Tinea capitis (scalp)
- “black dot ringworm” due to hair breaking
- patchy alopecia due to fragile hair
- non-scarring
- Kerions: pustule formation with inflammation
Tinea corporis (body)
- round-irregularly shaped
- “ringworm” with inflammed advancing edge and centre of clearing
- can be multiple (usually sequential appearance due to self inoculation)
Tinea pedis (foot)
- side of foot (dry and scaling)
- interdigital webspace –> inflammed and macerated (skin sloughed off with tissue exudate)
- -> increases risk of secondary bacterial infection causing septicaemia, cellulitis, wet gangrene
Tinea unguium/ Onychomycosis (nails)
- distal lateral subungal (DLSO): distal, lateral border; underside of nail plate trying to reach nail bed; thickened and discoloured nail with onycholysis (if >1/2 nail affected = already wks to months)
- superficial white (SWO): dorsal nail plate with whitish discolouration; edges are normal
- proximal subungal (PSO): proximal nail fold, proximal nail plate; marker of AIDS
Dermatophytosis: diagnosis
Clinical (mostly)
Signs and symptoms
Wood’s lamp (UVA) for microsporum species (fluorescence) but negative result can’t rule out infection by other 2 species
Lab:
- direct examination (wet mount MICROSCOPY) of SKIN SCRAPINGS, NAIL CLIPPINGS, HAIR
—> KOH preparation with Parker ink to highlight fungal hyphae (segmented branched)
==> 30% positivity rate; absence can’t rule out, presence is useful but can’t confirm species
- CULTURE: SABOURAUD DEXTROSE AGAR +/- selective agents e.g. cycloheximide or antibacterials
–> 25 degrees for 2-8 wks
==> reference method to confirm identity of fungi (macroconidia and microconidia) which may be important to identify clustering - molecular diagnostics not cost-effective
Dermatophytosis: treatment and prevention
Glabrous skin (without hair)
- topical antifungals (apply 2.5 cm beyond lesion) for 3 weeks to complete exfoliation of stratum corneum – NEED GOOD COMPLIANCE!
- oral antifungal for extensive lesions, failed topical therapy
Nail
- SWO, DLSO with <50% nail involvement and lack of lunula involvement –> topical antifungals for 6 mnths (fingers) or 12 mnths (toes)
- PSO, DLSO >50% nail with lunula involvement, Total dystrophic onychomycosis –> oral antifungals for 6wks (fingers) or 12 wks (toes)
Tinea capitis
- topical treatments difficult to penetrate follicles
- systemic antifungals for 6-12 wks
- antifungal shampoo 2 times/wk; household members use for 2-4 wks to treat carriers
Non pharmacological treatment:
- cleanse daily with soapy water
- keep lesion dry
- nail avulsion (removal) with antifungals after
Prevention:
- avoid communal use of footwear, towels, combs
- treat family members/pets
Superficial infections: Tinea versicolor - organism, clinical disease, diagnosis, treatment
Malassezia furfur
- lipophilic dimorphic fungi
Hypo/hyperpigmentation of skin
(diagnosis: KOH wet mount of skin scrapings)
Treatment: topical antifungals for 2 weeks, dyspigmentation may persist despite treatment
- oral antifungal if failed topical
Superficial infections: Oral candidiasis - risk factors for infection, clinical features, treatment
Candida
- normal flora of oropharyngeal and GI tract
- kept under control by T cell immunity
Risk factors:
- co-existing bacterial flora
- low salivary flow rate
- iron deficiency (mildly immunosuppressive)
- DM, HIV with low CD4, metred dose inhaled steroids
Clinical features:
- asymptomatic
- pain, altered taste
- dysphagia, odynophagia, retrosternal pain
- whitish plaques (bedside diagnosis): underlying erythema and slight bleeding
Treatment:
- Troches
- swish and swallow 1-2 weeks
Superficial infections: Candida vulvovaginitis - risk factors for infection, clinical features, diagnosis and treatment
Candida as part of normal flora
Overgrowth when normal flora are disrupted (hormonal imbalance)
e.g. estrogen replacement therapy, contraceptive pills, DM
Clinical features:
- pruritus vulvae
- whitish discharge
Diagnosis:
- clinical: speculum (self diagnosis in recurrent infection with menstruation)
- lab dx only if recurrent
Treatment
- topical antifungal (vaginal pessary)
- oral antifungal
Subcutaneous infections: Eumycetoma - organism, risk factor/transmission, clinical features, diagnosis, treatment
Mycotic mycetoma; various fungi possible
Chronic subcutaneous infections (uncommon in HK)
- inoculation of exposed skin by env. fungi e.g. feet (walking barefoot)
Clinical features:
- slowly growing nodules
- TRIAD: tumour (not malignant!), sinus, macroscopic grains
Diagnosis:
- examine grains, discharges, tissue biopsies for fungi
- tissue biopsy to rule out CA
Treatment:
- prolonged antifungal treatment (12 months - 3 yrs)
Subcutaneous infections: Sporotrichosis - organism, source, clinical features
Sporothrix schenckii
- dimorphic fungi
Traumatic implantation from rose thorns (Rose Gardener disease)
Clinical features:
- lymphangitis, lymphocutaneous spread
Invasive infections: Candidaemia - risk factors, complications, diagnosis, treatment
Risk factors:
- central venous catheters
- ICU stay (usually very ill)
- total parenteral nutrition use
- > 3 classes of antibiotics
- recent major surgery especially GI
- neutropenia
- prematurity
- malignancies/chemoRT/ immunosuppressants/ transplant recipients
Complications (dissemination)
- hepatosplenic candidiasis – multiple small abscesses seen on imaging
- endocarditis (IVDA)
- endophthalmitis (vitreous infection via retinal arteries)
- arthritis
Diagnosis:
- consider if persistent fever/illness after stating multiple antibiotics in high risk patients
- CULTURE: blood, using automated broth; sterile body fluids/tissue e.g. joints, vitreous
- Serology: Ag detection of mannan/beta-D-glucan; nucleic acid detection by PCR
Treatment
- systemic antifungals (IV or PO) for 14 days after last positive culture
Invasive infections: Aspergillus - species, classical morphology, clinical diseases, details of ABPA and aspergilloma
Aspergillus fumigatus (>50% invasive cases) Aspergillus flavus (aflatoxin)
(KOH wet mount: SEPTATED hyphae branching at ACUTE ANGLES; conidia)
(Culture: top smoky green with conidia and bottom yellow)
Clinical diseases;
- ABPA - allergic bronchopulmonary aspergillosis
- aspergilloma
- invasive aspergillosis
ABPA: conidia (fungal spores) are allergens which are inhaled from environment
- -> normal immunocompetent people asymptomatic
- -> sensitise host = asthma, rhinitis
- -> NO INVASION
- -> mucous as specimen for Ix
Aspergilloma: fungal balls due to colonisation of airways
- -> usually incidental finding of lesion on CXR
- -> background of pre-existing structure defect e.g. old TB
- -> may grow and erode into tissues/vessels causing haemoptysis –> need surgical removal
Invasive Aspergillosis - effects on lungs, risk factors, clinical features
In very immunocompromised patients
Exposure to spores is common
–> hyphal formation in pulmonary parenchyma and invades into vessels (angioinvasion) ==> bleeding and haemoptysis with high mortality rate
Risk factors:
- neutropenia
- HSCT
- glucocorticoid
- post-transplant: HLA mismatch (early). Graft versus host disease, CMV disease (late)
- cytopenia, Fe overload (causes fungal overgrowth)
Clinical features: (varying anatomical sites involved)
- pulmonary - chest pain, SOB, haemoptysis, fever
- tracheobronchitis (if lung transplant, AIDS)
- sinuses - rhinocerebral (in neutropenia)
- skin - through direct trauma/inoculation or dissemination
Invasive Aspergillosis - diagnosis
Definitive
- CULTURE of STERILE SPECIMENS e.g. lung biopsy (but note that may not be feasible as patients have strong bleeding tendency) – septated dichotomous hyphae
- histological proof in tissue/invasion
- poor sensitivity
Culture of other specimens
- BAL if appropriate signs and symptoms –> sensitivity 50%
- sputum (not very good specimen) PPV 80% in leukaemia
Invasive infections: Mucorales - species, classical morphology and characteristics, exposure, clinical disease
Zygomycetes (Rhizomucor, Mucor, Rhizopus)
Ubiquitous
Morphology: broad IRREGULAR hyphae (5-15 mcm), NON-SEPTATED
Fragile organism – low yield on culture; MOLECULAR OR SEROLOGICAL DX (specific T cells detected by ELISA)
Survive in high BG environment e.g. DM
Siderophore
- increase Fe uptake to stimulate fungal growth (deferoxamine for Fe overload)
Human exposure via inhalation of spores is common
- -> nasal/pulmonary
- -> angioinvasive (infarction and necrosis of tissue)
==> Rhino-orbital-cerebral mucormycosis
