What does the idiom bitten by bug mean?

To be inspired or excited about something.

The idiom dates back to the Middle English word bitten, which could mean both "to bite" and "to take hold of." In the 16th century, the idiom was used to describe a person who was bitten by a snake, which was thought to cause "love fever" or "love madness." By the 19th century, the idiom had taken on its current meaning of "to be inspired or excited about something."

For example, if you say, "I was bitten by the travel bug," it means that you have a strong desire to travel the world.