Fascinates one doctor in case of rabies (6)
I believe the answer is:
rivets
'fascinates' is the definition.
'one doctor in case of rabies' is the wordplay.
'one' becomes 'i' (Roman numeral).
'doctor' becomes 'vet' (vet is a kind of doctor**).
'in' means one lot of letters goes inside another.
'case of' means to remove the middle letters (outsides of).
'rabies' with its middle taken out is 'rs'.
'i'+'vet'='ivet'
'ivet' inserted inside 'rs' is 'RIVETS'.
(Other definitions for rivets that I've seen before include "Small pins for joining metal sheets" , "Short metal pins" , "Steel pins holding metal sheets together" , "Metal pins or bolts for holding together two plates of metal" .)