Gone off to follow the course of virus, say (8)
I believe the answer is:
pathogen
'virus say' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.
'gone off to follow the course' is the wordplay.
'off' indicates an anagram.
'to follow' says to put letters next to each other (some letters go after or follow others).
'the course' becomes 'path' (path can mean a route or course).
'gone' anagrammed gives 'ogen'.
'ogen' put after 'path' is 'PATHOGEN'.
'of' is the link.
Can you help me to learn more?
(Other definitions for pathogen that I've seen before include "It makes us sick" , "cause of illness" , "Disease-causing agent" , "it may make one sick" , "Disease-causing micro-organism" .)