Disease magician catches close to London (5)
I believe the answer is:
mange
'disease' is the definition.
(I know that mange is a type of animal disease)
'magician catches close to london' is the wordplay.
'magician' becomes 'mage'.
'catches' indicates putting letters inside.
'close to' indicates one should take the final letters (the 'close' to the word).
The last letter of 'london' is 'n'.
'mage' placed around 'n' is 'MANGE'.
(Other definitions for mange that I've seen before include "disorder" , "Skin disease affecting hairy animals" , "Itchy disease in dogs, etc" , "Canine skin disease" , "Disease in dogs causing hair loss" .)