This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
Infectivity of chicken pox last for : 
Select and explain. 
A. Till the last scab falls off, B. 6 days after onset of rash, C. 3 days after onset of rash, D. Till the fever subsides
B: 6 days after onset of rash
Answer: B: 6 days after onset of rash 
Explanation: “Period of communicability of varicella range from 1 to 2 days before the appearance of rash, and 4 to 5 days there after.”
Park 18/e, p 123
The patient ceases to be infectious once the lesions have crusted.
Scabs are not infective. So, option “a” is wrong.
Important features of chicken pox :

Causative Agent - Varicella zoster virus (HHV type 3)
Incubation period - 14 to 16 days
Secondary attack rate - 90%
Rash