A role played by church in infectious disease (7)
I believe the answer is:
cholera
'infectious disease' is the definition.
(cholera is a kind of infectious disease)
'a role played by church' is the wordplay.
'played' indicates anagramming the letters.
'by' says to put letters next to each other.
'church' becomes 'ch' (common abbreviation**).
'a'+'role'='arole'
'arole' with letters rearranged gives 'olera'.
'olera' after 'ch' is 'CHOLERA'.
'in' is the link.
(Other definitions for cholera that I've seen before include "A severe intestinal disease, severe Asiatic kind" , "Infectious and often fatal intestinal disease (7" , "could kill you" , "Acute intestinal infection from contaminated water or food" , "Intestinal infection caused by contaminated water or food" .)