The best paraphrase of the excerpt from the text is:
The team then measured the number of viruses stuck to each bee. This is because viruses can get stuck to the bee without infecting them. They also tested each bee for virus genetic material that would show if they were infected.
This paraphrase captures the main ideas from the passage, including the distinction between being exposed to a virus and being infected, and the methods used by the researchers to assess both exposure and infection.