Some, though not all, diseases can spread from a human to some, though not all, animals, and vice versa. The question is this: if a disease can spread from a human to, say, a dog, does that always mean it can spread from a dog to a human as well? In other words, is disease-spreading always two-way?
I remember being told there was a disease of some sort that horse’s get (it’s very rare) that can be transmitted to humans, and vice versa … but that may not be totally true
Yes.
If a disease affects two different species of critter, then it can be passed from dog to man, and then from man to some other dog, depending on the method of transference.
Rabies is an excellent example.