yes... diseases in those exposed for the first time can be an issue due to not having built up an immunity to them.
The Europeans had been through their plagues, etc. and the settlers had certain immunities to certain diseases, however things as simple as the flu, colds, and small pox took their tolls on them too...heck, many did not survive the voyage across the Oceans.
The Europeans were a dirty lot too... raw sewage running through the streets, etc.
And the disease issue, as I stated goes both ways...
settlers had major issues with things such as malaria... which the natives seemed to have built up a degree of immunity to.