Capital letters for a feverish complaint (6)

I believe the answer is:

prague

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'capital' is the definition.
(Prague is an example)

'feverish complaint' is the wordplay.
'feverish' becomes 'pr' (I can't justify this - if you can you should believe this answer much more).
'complaint' becomes 'ague' (ague is a kind of disease).
'pr'+'ague'='PRAGUE'

'letters for a' is the link.
This may not be right. Some or all of it may belong to another bit of the clue.

Can you help me to learn more?

(Other definitions for prague that I've seen before include "Gear up for this European city" , "European capital" , "Czech Republic's capital" , "Rather quiet" , "Capital city of Czech Republic" .)

I've seen this clue in the Evening Standard.

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