Spotty viral infection (7)
I believe the answer is:
measles
'spotty viral infection' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for measles that I've seen before include "Children's viral disease" , "Disease suffered in childhood" , "I appear as 8 [RASH]" , "Ailment" , "Childhood viral disease" .)