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What is Fever stops and rash begins is diagnostic of – and explain in detail?
Roseola infantum (Sixth disease or exanthem septum)

It is caused by human herpesvirus-6 (HSV-6)
Similar illness is caused by Parvovirus B-19 and Echovirus.
Age group involved is 6 mt to 3 yr.
Incubation period → 5 to 15 days.

Clinical manifestations

Abrupt onset with high-grade fever, mild pharyngitis and Coryza.
The temperature comes down rapidly in 3 to 4 days when a macular or maculopapular rash appears, starting from the trunk and sometimes extending to the extremities and face.
The rash lasts for 24 hours, and disappear in 1-2 days without pigmentation or desquamation.
There is occipital and post-auricular lymphadenopathy.