From the new char poor Leo caught the disease (7)
I believe the answer is:
cholera
'disease' is the definition.
(cholera is a kind of disease)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for cholera that I've seen before include "Contagious disease" , "Disease caught from contaminated water" , "Solemn promise" , "Acute infection caused by contaminated water or food" , "Disease contracted from infected water" .)