Crossword Genius

Half a dozen Russians contract an infectious disease (5)

Ross

I believe the answer is:

virus

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'disease' is the definition.
(I've seen this before)

I can't explain the rest of the clue.

Can you help me to learn more?

(Other definitions for virus that I've seen before include "Infective particle" , "computer problem" , "Electronic threat" , "Hidden destructive code in a computer program, or cause of illness" , "Cause of infection (in people and computers)" .)

I've seen this clue in the Sydney Morning Herald.
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