Good question! You’re right that animals don’t go for visits to the doctor when they’re in the wild, so I understand why you would think that if they’re alive they must have strong immune systems to fight off whatever bad things are in the environment (or in the food they eat). However, it’s likely that animals have strong digestive systems that are able to destroy any harmful viruses, bacteria, or other parasites that might make them sick. Animals’ digestive systems are what allow them to cope with things in the stuff they eat, instead of their immune systems.

It’s also important to consider that humans are animals too - we’re mammals, and share a similar immune system with other animals that are also mammals. Animals, including humans, all get sick - the difference is in the way that sickness plays out. For animals (that aren’t humans), it’s likely that they’ll die from their illness; on the other hand, humans go to the doctor, get medicine, etc. Think about what would happen if we didn’t have doctors - we’d probably succumb to the same fate as animals. This is why animals in zoos and aquariums are able to live for much longer than their wild counterparts: they are able to be taken care of by vets and are provided the same kind of healthcare that humans receive.

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