When a pathogen leaps from some nonhuman animal into a person, and succeeds there in making trouble, the result is what's known as zoonosis. It's a word of the future.
The word Zoonosis is unfamiliar to most people. But it helps clarify the biological reality behind the scary headlines about bird flu, SARS, other forms of nasty diseases, and the threat of a coming pandemic. It says something essential about the origin of HIV. It's a word of the future, destined for heavy use in the 21st century.
Ebola is a zoonosis. So is bubonic plague. So are yellow fever, monkeypox, bovine tuberculosis, Lyme disease, West Nile fever, Marburg, many strains of influenza, rabies, hantavirus pulmonary syndrome, and a strange new affliction called Nipah, wich kills pigs and pigs farmers in Malaysia.
The preceding excert is from National Geographic Magazine (October 2007).
They have a fascinating article on how we exchange diseases with animals and how globalization (and mostly the ease to travel averywhere) will have a major impact on our health.
And if the subject interrests you, you must also read Jared Diamond's Pulitzer Prize book Guns, Germs and Steel.
And you thought that extreme sports were dangerous...