How are animals infected with viruses or

bacteria?

If an animal hunts an animal and the prey has a virus the predator can get the virus leading the virus to spread.

I'll take a gander at your question

Explanation:

A Virus that can infect an animal, is called a zoonotic virus

Let's give an example of, let's say, a predator

A Fox is hunting down a rabbit, the rabbit has a zoonotic virus, the fox kills the rabbit, eats the rabbit, then obtains the virus.

It's just like if a person were to eat an infected person, they'd contract the virus.