How about some anti-plague vaccine?
I’d have all my shots done, like for a trip to Uganda.
A lot of pathogens that beset us today did not exist in 742 AD. AIDS is one obvious one, the common cold was not recorded prior to 1660. The plague only goes back to 1340, malaria maybe 1600. In prehistorical times, deadly pathogens would kill off a local population and then, they would die out because there was no one left to infect. Diseases like smallpox and leprosy persisted because they took longer to do kill a person. We are the descendants of the survivors, the people who had resistance to the worst pathogens. Native Americans, for instance, did not, so when they contacted Europeans, their populations had not been through the winnowing process.
Tetracycline will work just fine.
Nah, all you need to do is stay away from rats and lice, and bathe.