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As the flu got a cousin ill (10)

Ross

I believe the answer is:

contagious

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'as the flu' is the definition.
I can't tell whether this definition defines the answer.

'got a cousin ill' is the wordplay.
'ill' is an anagram indicator.
'got'+'a'+'cousin'='gotacousin'
'gotacousin' with letters rearranged gives 'CONTAGIOUS'.

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(Another definition for contagious that I've seen is " Catching".)

I've seen this clue in The Times.
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