Our immune system works pretty much the same way as the immune system of almost every other vertebrate (animal with a backbone and skull).

We have some passive systems like a tough skin, mucus, friendly bacteria, saliva, and such that help us keep germs from entering our bodies. Stomach acid helps to kill the germs in food. We have an inflammation response that happens when we have an injury. A bunch of cells go to the cut and start eating any germs they find. Blood and other fluids go to the spot to bring resources and more cells. Our skin gets warm, swells, and gets darker (or red if we have pale skin). The swelling also hurts. There are also cells in our body that find invaders and kill them directly or by making antibodies that stick to them.

I think I know why you’re asking why animals have a stronger one. After all, we wash our hands after using the bathroom and before we eat. Meanwhile a dog will drink right out of the toilet or eat garbage it finds on the sidewalk. Vultures each animals that have been rotting in the sun for days. The dogs and the vultures seem to be fine. What’s going here?

One thing that may be going on is that dogs without strong immune systems probably die young. Dogs with genes for strong immune systems are more likely to survive and pass along their genes. A different kind of adaptation can happen during our lives. The same is true for vultures.

Immunity can also improve during our lives. When individuals (dogs, humans, or vultures) are exposed to germs, our immune systems not only respond right away, they have memory cells that keep the body alert for that germ in the future. It’s kind of like a police station keeping wanted posters on the wall. Dog and vulture immune systems have been introduced to a lot more germs than our immune systems have been.

A research team looked at the genetics behind the immune system of one species of vulture and found a few things that help vulture eat a pretty nasty diet. For one thing, their stomachs make a lot of very strong acid. Their stomachs are at least 10 times more acidic than our stomachs. Sometimes 1000 times as acidic. Some vulture live on bones that their stomach acid break down. Vulture genes also seem to code for cells in the immune system that are especially good at finding and destroying germs. Another thing vultures have going for them is that their bald heads and necks may also help keep them clean. Feathers dipped in dead things day after day would get pretty nasty. Vultures also eliminate all over themselves and their wastes kill germs. Amazing, right?

In places where lots of people and vultures live, diseases in humans go up when the vulture population goes down. Can you imagine why? Hint: what happens to cities when the garbage workers go on strike?

If you are interested in studying immunity, you can be an immunologist.

First, it is important to realize that humans are animals too. We are a particular kind of furry animal with a backbone, a group called mammals. I'm not aware of any evidence suggesting that our immune system is any weaker than those of other mammals. It's true that certain animals can eat disgusting stuff that would make us sick (think of condors, or what dogs sometimes eat off the street). These animals simply have stronger stomach acids than we do, not stronger immune systems.

Well, to start off, animals don’t have stronger immune systems than humans. Humans have the most complex immune systems of any organism. Also the word “strong” with respect to immune system can be a little confusing because a good immune response will be just enough to clear the infection without causing damage to the person. So really what you want is an “efficient” response, rather than a “strong” response. It turns out that all animals get sick too, they just can’t speak so it’s not as obvious. In fact, you might notice dogs sneezing every once in a while. And cats can get a virus similar to HIV, which causes AIDS.

Many frogs are in danger from a fungal infection that is wiping out tons of them across the world.

However, it is true that humans are much more likely than any other organism to get what are called autoimmune diseases in which case the immune system attacks the person. This is a case where the immune system is, in a sense, too strong. Because we have such an advanced immune system that can recognize any bacteria or virus, occasionally the body mistakes a human cell as an invader and attacks it.

This doesn’t happen in organisms with simpler immune systems such as insects or sea urchins. So to sum up, all living things can get sick and in many cases, huge animal populations will die off because their immune system wasn’t good enough to fight off an infection.

They don't - actually, humans have quite strong immune systems. There are species that have been driven extinct by devastating plagues, but while human beings have had such plagues, our species has survived.

Other animals don't show when they're sick the way that humans do. This is because of natural selection: if they showed sickness or weakness, they would die, because they couldn't find food, or predators would kill them and eat them. This means that when other animals do appear sick, it's usually because they're about to die of the sickness. Humans, on the other hand, don't have to worry about starving because of a cold or flu, and usually don't have to worry about being eaten either, so we can show symptoms of our illness while we fight said illness off.