Cell mediated immune defect.

What is the portal of entry of this organism and why does it localize to the CNS?

• Cryptococcal inhalational exposure is common.
• Although the lung is the portal of entry, pulmonary disease is uncommon. 
• Cryptococcus has a metabolic affinity for catecholamines (CNS is rich in catecholamines) which may explain its tropism for the CNS.
  
  

Describe virulence characteristics of this pathogen.

• Cryptococcus has a polysaccharide capsule which blocks opsonophagocytosis via both the classic and alternate complement pathways.
• Encapsulated yeast are able to resist intracellular killing by polymorphonuclear cells and macrophages. 
• Circulating capsular polysaccharide induces T cell tolerance and anergy. 
• Host inflammatory reaction to cryptococcus is minimal.
  
  

Describe diagnostic procedures for this infection. 

• CSF and serum detection of capsular antigen by later agglutination and culture of blood and CSF. 
• Occasionally skin lesions can be biopsied. 
• Routine stains are unhelpful and special stains such as silver, PAS and mucicarmine stains are required.
  
  

What treatment would you prescribe?

• Amphotericin B in combination with 5FC is the treatment of choice initially.
•  In HIV /AIDS, chronic suppression with fluconazole is required to prevent relapse.