“One False Step” is episode nineteen of season two of Stargate SG-1.
After a UAV crashes during a testing mission, SG-1 return to the planet to recover it and find out what went wrong.
They meet some rather odd natives who don’t appear human.
Daniel had some sort of illness when they arrived, and the natives start keeling over. The team then have to try and find out what’s causing this. Especially as it starts to spread to SG-1.
There is an indirect reference to European diseases that wiped out entire populations, especially in the Americas, as natives with no immunity were exposed to new diseases. Although I think it would be a bit trickier to spread one to a new species, rather than another bunch of humans.