<prompt> Infectivity of chickenpox lasts for:Till the last scab falls off6 days after onset of rash3 days after onset of rashTill the fever subsides  <response>: Ans. b 6 days after onset of rash Period of communicability of varicella range from 1 to 2 days before the appreance of rash, and 4 to 5 days there after. The patient ceases to be infectious once the lesions have crusted. Scabs are not infective So, option a is wrong. Impoant features of chickenpox Causative agent - Varicella zoster virus HHV type 3 Incubation period - 14 to 16 days Secondary attack rate - 90 Rash Chickenpox Smallpox Superfici Deep seated Pleomorphi Only one stage of rash at 1 time Centripet Centrifugal Unilocular Multilocular Dew drop like appearance Umbilicated Inflammation nt No area of inflammation around vesicle Mostly flexor surface Mostly extensor surface 