Leave affected by case of dengue (6)
I believe the answer is:
decamp
'leave' is the definition.
(decamping is a kind of leaving)
'affected by case of dengue' is the wordplay.
'affected' becomes 'camp' (I've seen this before).
'by' says to put letters next to each other.
'case of' says to hollow out the word (remove centre letters) (outsides of).
'dengue' with its middle removed is 'de'.
'camp' after 'de' is 'DECAMP'.
(Other definitions for decamp that I've seen before include "escape" , "Make off secretly" , "Fold up tents and depart" , "Fold up tent and depart" , "Make sudden breakaway" .)