African bug left, because harmless? Not quite so (5,5)
I believe the answer is:
lassa fever
'african bug' is the definition.
The definition suggests a singular noun which matches the answer.
'left because harmless? not quite so' is the wordplay.
'left' becomes 'l' (common abbreviation).
'because' becomes 'as' (I've seen this in other clues).
'harmless?' becomes 'safe' ('safe' can be similar in meaning to 'harmless').
'not quite' means to remove the last letter (most but not all of the word).
'so' becomes 'very' (I've seen this in another clue).
'very' with its final letter taken off is 'ver'.
'l'+'as'+'safe'+'ver'='LASSA FEVER'
Can you help me to learn more?
(Other definitions for lassa fever that I've seen before include "Tropical viral disease that could kill" , "ailment" , "Acute viral disease" .)