Plain guest, avoiding pair on right with infectious disease (6)

I believe the answer is:

plague

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'infectious disease' is the definition.
(I know that plague is a type of infectious disease)

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for plague that I've seen before include "Deadly epidemic" , "Large-scale illness" , "Contagious disease that spreads rapidly and kills many" , "dog" , "Outbreak of a deadly disease, or infestation of pest like locusts" .)

I've seen this clue in The Irish Times.

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