have the bug
To suddenly be excited by or very interested in something (which can be specified between "the" and "bug"). Molly's really enjoying rehearsing for the school play—it seems she has the acting bug.
have (or be bitten by) the bug
develop a sudden strong enthusiasm for something.be bitten by/have the ˈbug
(informal) have a sudden strong interest in or enthusiasm for something: My mum was never really interested in going abroad until she went to America last year. Now she’s been bitten by the travel bug and hates staying at home!