[cm2187]

Not just syphilis. Tropical diseases like yellow fever and malaria decimated european settlers for centuries. That's a large part of why Haiti could break free from France for instance, France would send troops, half of which were dead within months from diseases.

That's also what protected inland parts of Africa from colonisation until the XIX century.

[inglor_cz]

The diseases that you mention are of African origin and, when introduced into the New World, massacred the natives almost as efficiently as smallpox.

Africa is a huge cauldron of human pathogens, which is not that surprising, given that hominids developed there. As a rather tragic consequence, Africans were sought after as slaves, because they were resistent to many of the diseases that killed white or Amerindian indentured workers.

[BurningFrog]

It was also a major reason for bringing in Africans slaves to work the fields, as they survived much longer that Europeans.

[Symmetry]

Yellow fever and malaria were brought to the New World by Europeans.