Doubter infected with cholera, initially (7)
I believe the answer is:
sceptic
'doubter' is the definition.
('sceptic' can be a synonym of 'doubter')
'infected with cholera initially' is the wordplay.
'infected' becomes 'septic' ('septic' can be similar in meaning to 'infected').
'with' indicates putting letters inside.
'initially' indicates taking the first letters.
The initial letter of 'cholera' is 'c'.
'septic' enclosing 'c' is 'SCEPTIC'.
(Other definitions for sceptic that I've seen before include "He's hard to convince" , "One who doubts the truth of religions" , "One is inclined to doubt accepted opinions" , "One habitually doubts accepted beliefs" , "Person who tends to disbelieve" .)