system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What keeps oceans and seas from spreading viruses and many other contagious illnesses?
gpt
Nothing really. If you have an open wound in ocean water, you'd better clean it out very well to avoid bacterial infections. 

But since humans and primates don't normally live in the ocean, there's not a lot of ocean born diseases and viruses adapted to infect us. Plenty of nastiness going around for sea life though.