Zoonotic Diseases

Zoonotic diseases, or zoonoses, are infectious diseases that can spread between animals (vertebrates) and humans. Vertebrates are animals with a backbone, like cows, sheep, rats, dogs, cats, bats and birds. The way their bodies work is similar enough to ours that pathogens (germs) can sometimes adjust to live in both.

Some zoonotic diseases only spread from animals to humans and don’t spread from person to person. Others, like Ebola, spread from animals to humans and continue to spread in humans, causing periodic outbreaks of illness. Still others spread to humans and then mutate to only infect humans, like HIV and COVID-19. Once they only spread in humans, they’re no longer considered zoonotic (but other forms of the disease can still exist in animals).