Most native societies had much higher hygiene standards (generally cleaner) than European settlers. Also most native societies were sheltered from other people, unlike European settlers who had exposure from Africa and Asia.
So most native societies were not as capable to withstand all the new bugs the Europeans brought with them.
That being Syphilis is a purely native American disease that the European settlers were not resistant to. Though it was not nearly as deadly or contagious as the diseases the European settlers brought with them.
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