ZOONOTIC DISEASES
Zoonoses (singular: zoonosis; adjective: zoonotic) are diseases transmitted among humans and other vertebrates. The key word here is among. Zoonotic diseases can be transmitted from nonhuman animals (henceforth referred to as animals) to humans or from humans to animals. In this book the term zoonotic disease will refer to diseases transmitted from animals to humans.
Zoonotic diseases are not rare:
• All known microbial and parasitic categories include at least one zoonotic agent. From the smallest virus to the largest parasitic worm, there are many agents of disease, called pathogens, that can pass among people and animals (Box 1).
• A majority of infectious diseases are zoonotic. There are more than 150 diseases that are known to be zoonotic.
• Many human diseases probably started out as zoonotic diseases. Although we cannot be sure which diseases made the leap from animals to humans, there is evidence that measles, smallpox, and diphtheria came to us from animals. There is also compelling evidence that AIDS started in monkeys.
• About three quarters of emerging diseases are zoonotic, and when they appear, they can spread rapidly. The West Nile virus appeared in New York City in the United States in 1999 and moved through the country in the summer of 2002, causing human and equine disease and death.
• Most of the animals we come in contact with every day can be sources of zoonotic diseases (Box 2).
