Mycology

Question 1

What are all fungi?

Answer 1

Eukaryotes
Have rigid cell walls
They are unicellular or grow as hyphae (tubular, elongated, and filamentous structures which may contain multiple nuclei and extend by growing at their tips)

Question 2

Examples of fungal diseases

Answer 2

Athletes foot, thrush, ringworm

Question 3

When do fungal diseases often arise?

Answer 3

As oppportunistic infections - important in AIDS/immunocompromised

Question 4

What are some fungi of medical importance?

Answer 4

Cryptococcus neoformans (yeast)
Candida albicans (yeast)
Aspergillus (filamentous fungi)
Pneumocytis jiroveci (yeast)

Question 5

Describe Cryptococcus neoformans

Answer 5

This is a free-living encapsulated yeast; some species are associated with bird droppings (guano)

Question 6

Clinical disease of Cryptococcus neoformans

Answer 6

Infection of immuno-competent patients is very rare
Infection more common in HIV+ patients with CD4+ <200, or people who have just had organ transplants or are on long-term steroids
Self-limiting pneumonia, cryptococcoma (large fungal mass), skin infections (cryptococcosis – rare but long-lasting), meningitis
Treatment to eradicate fungus is essential in case of CNS involvement – oral and IV anti-fungals include Fluconazole, Nystatin, Amphotericin B

Question 7

Describe Candida

Answer 7

Candida is a yeast that is part of the normal mouth, gut and vagina microbiome (commensal)
It can grow as a yeast, pseudohyphae and hyphae – hyphae are a big challenge to professional phagocytes

Question 8

When can candida infections become a problem?

Answer 8

If the normal microbiome is disrupted (eg. following antibiotic treatment), Candida infections can become a problem – the big problem is not local infection but systemic candidiasis, nearly always a result of immunodeficiency

Question 9

Describe candidiasis

Answer 9

Mucocutaneous candidiasis takes three forms – oropharyngeal (OPC), esophageal, vulvovaginal
Very common in untreated HIV+ individuals, appearing long before other opportunistic pathogens
OPC (thrush) is very painful – can seriously affect nutrition and taking oral medication (culture methods usually not needed to make diagnosis)
Systemic anti-fungal treatment of choice is Fluconazole 100-400mg/day for 2-3 weeks
Invasive disease – clinical clues: unexplained fever which is not responsive to antibiotics, multiple non-painful cutaneous lesions; laboratory tests: neutropenia <100 PMNs per mm3, yeast in urine sample, IV catheter culture grows yeast
Typical patients: neonatal Gi surgery, ICU patients, septic shock, burn patients, long-term corticosteroids, solid organ transplant recipient, BMT recipient prior to engraftment or in GVHD, post broad-spectrum antibiotics

Question 10

Describe Apergillus

Answer 10

Aspergillosis is infection by an Aspergillus spp fungal species which are ubiquitous in the environment
Rare in immuno-competent patients, but can be seen where there is repeated tissue damage and scarring (eg. COPD or TB or bronchiectasis)
Invasive aspergillosis has a high mortality rate (>25%) and is found in patients with neutropenia, long term steroid treatment, lung transplant recipients, later stages of HIV AIDS, sometimes in leukaemias
Chest X-ray shows a rounded density in right mid-lung, with an ‘air crescent’
Treatment – anti–fungals as above

Question 11

Describe Pneumocystis

Answer 11

east-like pathogen (formerly thought to be a protozooan).
Classically Pneumocystis pneumonia defined AIDS as a syndrome
Can be found in the lungs of healthy people but is a classic opportunistic pathogen that causes pneumonia only in the immuno-compromised
Non-productive cough, weigh loss, night sweats, chest X-ray shows widespread infiltrates, non responsive to antibiotics.
Definitive diagnosis from BAL – see characteristic cysts (“crushed ping-pong balls”)