i imagine this problem is negligible because of how easily people can travel. diseases don’t stop spreading when they see a political border, and there are plenty of other places in the world that are much more remote and more likely to have diseases americans are not resistant to
i heard a similar idea that if humans can’t see air then maybe undersea creatures can’t see water. so fish would be like birds and crustaceans would be like land dwellers. so yeah jellyfish being storm clouds checks out