why do viruses move between species sometimes and other times not?

Question

why do viruses move between species sometimes and other times not?

In: 1

Answer 1

The virus is designed to interact with certain types of cells of the infected species in order to infect them. It is possible – nay, probable – that the virus gets into a different type of animal and just doesn’t interact with anything in that species because there’s no match for the cell types. No harm done.

Of course, the virus is still a physical thing and could still get passed to a different species again, or back to the same species it originally came from. But this intermediate animal doesn’t care.

It’s actually rare for a virus to be able to interact with multiple different types of animals.