Of course, close contact with farm animals is a major vector for new viruses (like pox and covid). There's a reason life expectancy was significantly lower in the Middle Ages, especially for young children.

I'm also a medieval reenactor :D 14th century mercenaries. If you think about it, we "cheat" all the time by having tents for everyone, plenty of food, sanitary facilities (even if it's only portaloos), being vaccinated, etc. Campaign life would be a lot less enjoyable if we actually kept it authentic.