Answer :

Causative agent:

1. Bilirubin - a waste material in the blood.
2. Vibrio cholerae - Its tranmitted to humans through faceal-oral route ; A bite of contaminated food, etc.
3. HIV (Human immuno deficiency Virus) - HIV-1 (this has led to the worldwide pandemic), HIV-2 (Less virulent and less commen).
4. Varicella-zoster virus (VZV) - occurs mostly with contact with an infected person.