Girl infected with the French disease (7)
I believe the answer is:
malaria
'disease' is the definition.
(malaria is a kind of disease)
'girl infected with the french' is the wordplay.
I cannot really understand how this works, but
'girl' could be 'mala' and 'mala' is found in the answer.
The remaining letters 'ria' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for malaria that I've seen before include "Infectious fever" , "Disease from bites by infected mosquitos" , "Mosquito-transmitted disease" , "Disease causing fever transmitted by mosquitos" , "Mosquito-borne disease" .)