Case 4:

A 30 year old man with HIV infection and CD₄ count of 75 was stable on zidovudine, Didanosine and trimethoprim/sulfamethoxazole. He presented to the hospital with fever and intractable headache for 10 days. On the day of admission , he developed nausea and vomited several times. On examination, he had photophobia and a temperature of 39.5C. CT scan was normal, lumbar puncture revealed an opening pressure of 200 mm of water (high). CSF analysis demonstrated 2 lymphocytes, glucose of 20 mg and a protein of 160 mg.

1. What host defect made this patient vulnerable to this infection?  Answer
   
2. What is the portal of entry of this organism and why does it localize to the CNS?  Answer
   
3. Describe virulence characteristics of this pathogen.  Answer
   
4. Describe diagnostic procedures for this infection.   Answer
   
5. What treatment would you prescribe?  Answer