Insects, not beginning to circulate disease (7)
I believe the answer is:
rickets
'disease' is the definition.
(rickets is a kind of disease)
'insects not beginning' is the wordplay.
'insects' becomes 'crickets' (cricket is a type of insect).
'not beginning' means to remove the first letter.
'crickets' with its first letter taken off is 'RICKETS'.
'to circulate' acts as a link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for rickets that I've seen before include "Bone disease, caused by vitamin D deficiency" , "Childhood disease caused by a deficiency of vitamin D" , "Bone-distorting disease" , "Children's disease" .)