Fungal Infections

Question 1

Dermatophytosis

Answer 1

• Infections of the skin, hair and nails caused by a group of keratinophilic moulds - dermatophytes or ringworm fungi
• Three genera of dermatophytes
  
  • Trichophyton
  • Microsporum
  • Epidermphyton
• ​Can be anthrpophilic, zoophilic or geophilic
• Cause of:
  
  • Tinea pedis
  • Tinea capitis
  • Tinea corporis
• Prevalance in at least 10% of UK adults
• Foot and nail infections due to *T.interdigitale *and T.rubrum most common
• Rx
  
  • ​Skin lesions - topical therapy
  • Scalp/nail infections - oral therapy

Question 2

Subcutaneous Mycoses

Answer 2

• The result of traumatic implantation of fungal spores
• Mycetoma - the most common presentation = a chronic localised destructive infection of the skin, subcutaneous tissue and bone of feet or hands
• Various species of fungi
• Most common in arid tropical or sub-tropical regions
• Often refactory to treatment
• Amputation may be indicated if ther is bone involvement
• Sporotrichosis - caused by implantation of *Sporothrix schenckii *–> nodules and areas of ulceration along the course of lymphatic channels

Question 3

Candidosis

Answer 3

• Infection caused by *Candida *fungi
• Commensal inhabitants of mouth and GI tract in 30-50% of people
• Opportunistic pathogens - infectious usually endogenous in origin
• Usually cause mucosal (thrush), cutaneous or nail infection
• May cause acute/chronic deep-seated infection in the debilitated or immunocompromised
  
  • Life-threatening problem in neutropaenic cancer patients and surgical/ICU patients (inc. neonates)
  • Diagnosis is difficult as non-specific S&S and unclear microbiological and serological tests
  • Rx - fluconazole and/or amphotericin B
• Oral candidosis most prevalent in small infants and old age
  
  • Occurs in more than 80% of patients with AIDs
• Vaginal candidosis (thrush) most common in pregnant women
• Antibiotic treatment and diabetes predispose to infection
• Candida species account for 8-10% of hospital aquired bloodstream infection-

Question 4

Cryptococcosis

Answer 4

• Infections caused by the encapsulated yeast Cryptococcus neoformans
• Global distribution
• Often isolated from soil and old dried bird faeces
• Infection follows inhalation
• Cryptococcal meningitis is the most common presentation
• 5-10% of European and North American AIDs patients, 30% of African - incidence
• Encapsulated cells often seen in CSF specimens
• Diagnostic test is for cryptococcal antigen
• Cryptococcosis = fatal if untreated
• Rx - amphotericin B + flucytosine in combination

Question 5

Aspergillosis

Answer 5

• Infections caused by moulds of genus Aspergillus - especially A.fumigatus
• Ubiquitous in soil, dust, air and on food
• Usually acquired from inhalation of spores
• Potent allergens may –> localised infection of lungs or sinuses
• Fungus ball (aspergilloma) may occur in patients with residual lung cavities
• In immunocompromised - especially neutropaenic - patients may –> widespread growth of fungus in lungs and dissemination to other organs
  
  • Mortality of invasive aspergillosis high - >90% in bone marrow transplant patients
• Outbreaks associated with building work
• Clinical presentation often non-specific - microbiological and serological tests unhelpful
• Rx - voriconazole is the treatment of choice for invasive aspergillosis
• Oral itraconazole may be used as prophylaxis in patients at risk of invasive disease

Question 6

Zygomycosis (Mucormycosis)

Answer 6

• Infections due to ubquitous thermophilic species of:
  
  • Rhizopus
  • Lichentheimia
  • Mucor
• ​Presents as:
  
  • Rhinocerebral mucormycosis
  • Cutaneous infection of wounds
• Occurs in patients with uncontrolled diabetes or neutropaenia
• Rapidly progressing disease with necrotic infarction
• Rx - refractory to treament: often requires surgical debridement
• Aggressive therapy with lipid forms of amphotericin or posaconazole