The natives of the Americas were faced with several new diseases at once creating a situation where some who successfully resisted one disease might die from another. Multiple simultaneous infections (e.g., smallpox and typhus at the same time) or in close succession (e.g., smallpox in an individual who was still weak from a recent bout of typhus) are more deadly than just the sum of the individual diseases. In this scenario, death rates can also be elevated by combinations of new and familiar diseases: smallpox in combination with American strains of yaws, for example.