Opportunistic Mycoses

Question 1

Opportunistic mycoses

Answer 1

• infections caused by fungi that are normally found as human commensals or in the environment
• can be catheter-related or more localised infections involving the lungs, skin and paranasal sinuses
• pose a diagnostic and therapeutic challenge

Question 2

Examples of opportunistic mycoses

Answer 2

• Cryptococcus neoformans

• • Candida albicans*
• • Aspergillus fumigatus*
• • Pneumocystis jiroveci*

Question 3

Cryptococcus neoformans biology

Answer 3

• encapsulated, yeast-like fungus
• replication by budding

Question 4

Cryptococcus neoformans virulence factors

Answer 4

• Extracellular polysaccharide capsule

: inhibits phagocytosis

: down-regulates Th1 response

*Th1 activates B-cells to produce antibodies

Question 5

Cryptococcus neoformans epidemiology & transmission

Answer 5

• worldwide distribution
• commonly seen in in patients with compromised cell-mediated immunity (e.g. AIDS and immunosuppressive conditions)
• present in soil
• transmitted in pigeon droppings
• usually acquired by inhaling from the environment

Question 6

Crytococcus neoformans clinical manifestations

Answer 6

- acute pulmonary disease

: usually associated with occupations around pigeons

: underlying respiratory disease

- cutaneous cryptococcosis

- encephalitis or meningoencephalitis

- fever, headache, visual disturbances, abnormal mental status, seizures

- increased intercranial pressure

* highly dependent on host immune status (but can still occur in immunocompetent hosts)

Question 7

Cryptococcus neoformans diagnosis

Answer 7

• capsulated yeasts can be seen in India-ink stained preparations of CSF
• latex aggultination test for the capsular polysaccharide antigen

Question 8

Candida albicans biology

Answer 8

• most frequently isolated human mycoses
• oval yeast-like forms that produce buds or blastoconidia & chlamydospores
• produce psuedohyphae and true hyphae
• forms germ tubes

Question 9

Candida albicans virulence factors

Answer 9

• phenotypic switching
• changing into different morphologies

: changes in the microenvironment

: enables Candida albicans to survive in many different environmental microniches within human host

Question 10

Candida albicans epidemiology & transmission

Answer 10

• endogenous & exogenous spread
• part of normal flora of diseased skin and mucousal membranes of GIT, UGT and RT (also found in the environment)
• increased risk with immunosupression
• nosocomial transmission

: common cause of nosocomial BSI (bloodstream infections)

: handwashing is important (can be spread on toilets)

• primary source of infection: the patient

Question 11

Candida albicans clinical manifestations: mucousal

Answer 11

- oropharyngeal candidiasis

: symptoms may be absent or include burning/dryness of the mouth, loss of taste, and pain upon swallowing

: white plaque resembling milk curd forms on buccal mucosa & (less commonly) on the tongue, gums, palate or pharynx

: not common in healthy adults, but can infect infants and elderly

- hematogenous candidiasis
: may be acute or chronic and usually involves Candida septicemia

Question 12

Candida albicans clinical manifestations: others

Answer 12

• vulvovaginal candidiasis
• skin infections
• GI candidiasis
• pulmonary candidiasis
• UT candidiasis
• meningitis
• endocarditis, myocarditis, pericarditis

Question 13

Candida albicans diagnosis

Answer 13

• microscopy & histology
• culture

Question 14

Each of the following statements concerning Cryptococcus neoformans are correct EXCEPT?

a. The initial site of infection is usually the lung
b. Its natural habitat is the soil, especially associated with pigeon feces
c. Pathogenesis is related primarily to production of exotoxin A
d. Budding yeasts are found in the lesions

Answer 14

c. Pathogenesis is related primarily to production of exotoxin A