Kind of infection (5)
I believe the answer is:
viral
'kind of infection' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for viral that I've seen before include "Go ___ (take off via the internet)" , "Pertaining to an ultramicroscopic infection" , "Spreading rapidly" , "Like some infections" , "as an internet sensation" .)