I think this is normal. Rescues just can't afford to take on that risk, unfortunately. It's one of the reasons that you want to give your foster animal at least two weeks of no contact with your household animals or strangers. That way you have enough time for any illnesses or behavior problems to come to light. If you have the patience to heed this recommendation then you will GREATLY reduce the chance that anything will go wrong.
For the first two weeks that I have a new foster, I keep the new animal in a room with no access to our other animals that can be easily sanitized. I also wash my hands before and after handling them and wear scrubs over my clothes, which may be overkill but it makes me feel so much better when I sit on our furniture or slip into bed knowing that stuff like ringworm, mange, Parvo, kennel cough and puppy poop has been safely left behind in the foster room. And if you are at all concerned about being bitten by your foster animal, contact the shelter immediately for advice. If your foster animal is mildly fearful, start slow, don't force anything and hand feed them all of their meals.
Good luck and thanks for fostering!
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