Dad later lets it own goal; it makes you sick (8)
I believe the answer is:
pathogen
'it makes you sick' is the definition.
The definition suggests a singular noun which matches the answer.
'dad later lets it own goal' is the wordplay.
I cannot quite understand how this works, but
'dad' could be 'pa' (both can mean one's father) and 'pa' is located in the answer.
'it' could be 't' (abbreviation. e.g. in 'tis) and 't' is present in the answer.
'own goal' could be 'og' (football abbreviation) and 'og' is present in the answer.
The remaining letters 'hen' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for pathogen that I've seen before include "Disease-causing organism" , "cause of illness" , "Disease-causing micro-organism" , "source of disease" , "Cause of disease" .)