I've always learned that during the Spanish conquest of the Americas that the native populations were plagued by diseases native to the Spanish, such as smallpox, because they had never built immunity to such diseases. Aside from the emergence of syphilis in Europe that seems to have originated from Latin America there does not seem to be any diseases that plagued the Spanish. I would imagine that the large empires of the Aztecs or Incas must of had some diseases within them, and there is no reason that the Spanish should have been exposed to these diseases beforehand, so I am having trouble understanding why the Spanish were not hampered by a Latin American disease in the same way.