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

Because bodies of different species work differently and a disease is ready to attack in a certain way which may not work on other species. Sometimes a species can be just a host in which a disease can survive but not reproduce