It's not "genocide" without intention. It's wrong to call the destruction of native culture by a disease "genocide." Without the eradication of the native populations of the Americas by disease, we would have had a different history. See the book "1491" by Charles Mann.
"...had a major impact on world history, not least because indigenous populations of regions where smallpox was non-native, such as the Americas and Australia, were rapidly and greatly reduced by smallpox (along with other introduced diseases) during periods of initial foreign contact,...."
Did the Europeans not know that thousands if not millions of people were dying of the pox? If they did then they had to know there was a possibility that it would follow then to the new world.