The infectivity of chicken pox lasts for -
Chicken pox

Causative agent → Varicella zoster virus (Herpes simplex type III).
Portal of entry → Respiratory tract or conjunctiva
I. P. → 10-21 days.
Infectious period → 2 days before and 5 days after the onset of rash.
Secondary attack rate is high → 90 %
Age group → 5-9 Yrs.
C/Fs - has two stages

1. Pre-eruptive stage

fever, back pain, malaise, shivering

2.Eruptive stage

Rash is symmetrical, mostly on flexor surface.
Centripetal in distribution
Mainly On trunk, less common on arms and leg
Palms and soles are not usually affected
There is rapid evolution of rash
Rash is plemorphic, that is, all stages of rash (Papule, vesicle and crusts) may be seen simultaneously.
Disease is more severe in adults than in children.
Till the last scab falls off
6 days after onset of rash
3 days after onset of rash
Till the fever subsides