I am reading a non-fiction account of Spanish first contact with native Americans. The Spaniards were shipwrecked, undernourished, malnourished, and dehydrated upon their arrival. Over 75% of them died within a few months. The author writes that after their numbers were thusly reduced, the natives who they were staying with then began to die of "a sickness of the stomach." The natives blamed the Spaniards for killing them.
I am assuming that the illness the natives contracted was introduced by the Spaniards, and that it was one of the ones for which the Europeans had developed a certain level of immunity, meaning that in effect, the natives were correct that the Spaniards were killing them.
The author does not ever specifically say whether any of the Spaniards contracted this fatal stomach illness, so it is possible that all of the Spaniards who died, did so from other causes, such as malnutrition. I am basically trying to find out how likely that is.
My questions are, would the Spaniards' immunity from whatever disease this was help them in the presence of an epidemic such as this, or did their immunity only keep them from contracting it when it was in its latent form? Did their weakened and malnourished state make them more susceptible to a contracting a disease they were carrying, yet were previously immune to?
To put it another way, I'm trying to find out whether it is possible for there to have been a "feedback loop" of some sort when it came to European-introduced diseases.