Complex sentence: Donwynn receives a video reply from Jerry, who tells him not to open the thermos, and that it contains a deadly virus that mutates human DNA and he tells Sam he plans to visit the hospital the next day.
Split into simpler sentences: Donwynn receives a video reply from Jerry, who tells him not to open the thermos because it contains a deadly virus that mutates human DNA. Donwynn informs Sam that he plans to visit the hospital the next day.