Originally Posted by
HooKooDooKu
I'm not a biologist, so this is just a logical guess (so don't take these statements as fact):
Human's don't get human diseases from horses, they get human diseases from other humans... and fecal transfer is one of the primary sources of disease transfer between human.
Now yes, there are things in horse poop, deer poop, and bear poop that can make you sick. That is why the park suggests boiling ALL water obtained in the back country. But when it comes to human poop, humans are limited to a relatively small percentage of the park, and multiple humans use this same area.
So in other words, there is a much higher likelyhood of disease transmission from human poop to other humans than there is from other animals. So humans must bury their waste to help offset this greater likelyhood of disease transmission.