That’s only the first question. Occam’s razor suggests that since almost no cases showed up prior to Columbus, that it was spread by his men. If a few cases show up before that? That’s not usually how infections spread it’s possible a weaker strain was here, maybe one that affected some other species and crossed over.

But if it means someone else got to the Americas first, that’s a cultural bomb that would immortalize your name for documenting. So it’s worth looking at it from one side or the other to determine if the second question is worth the payoff times the probability of being true.