Contaminate with disease (6)
I believe the answer is:
infect
'contaminate with disease' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for infect that I've seen before include "Impart a disease" , "Contaminate with disease" , "Contaminate, make ill" , "Transmit germs to" , "Affect (with a virus)" .)