Guard retaining energy after extremes of deadly disease (9)

'disease' is the definition.
(dysentery is a kind of disease)

'guard retaining energy after extremes of deadly' is the wordplay.
'guard' becomes 'sentry' (sentry is a kind of guard**).
'retaining' is an insertion indicator.
'energy' becomes 'e' (physics symbol as in E=mce).
'after' says to put letters next to each other.
'extremes of' says to hollow out the word (remove centre letters).
'deadly' with its centre removed is 'dy'.
'sentry' placed around 'e' is 'sentery'.
'sentery' put after 'dy' is 'DYSENTERY'.