Why are diseases more communicable within a species (e.g. human-to-human) than intraspecies (e.g. bird-to-human)?

Question

Why are diseases more communicable within a species (e.g. human-to-human) than intraspecies (e.g. bird-to-human)?

In: Biology

Answer 1

Think of it like a lock and key.

A virus’ proteins, for example, is a key and the host’s cell membranes have a specific lock. Sometimes, through chance mutation, the keys change to match the lock of host cell membrane allowing the virus to enter and replicate itself. The host is now infected.

So, the key that worked to get into the chicken’s cells now works to get into the human’s cells. It may also be that the virus possesses many keys.

This is how viruses and other pathogens can jump from animals to people.