Diseases From Animals: A Primer
A is for animals, Z is for zoonoses.
It's hard to think of a more horrible disease than Ebola hemorrhagic fever. Ebola virus is spread by contact with the blood or body fluids of an infected person. Does it come from animals? Probably. Monkeys and great apes get it -- and people can get it from them when they butcher them for food. But monkeys die of Ebola, so they can't be the ultimate host. Most researchers think there's an animal out there harboring the virus. They just haven't found it yet.
That SARS emerged in China's Guangdong province seems sure. What's not sure is where it came from. SARS is a coronavirus, but it's not like any other member of the coronavirus family. Some researchers think it may have come from an endangered animal known as a masked palm civet -- like most exotic animals, a culinary delicacy in parts of China. Others find the evidence weak. Whether SARS evolved in animals or humans remains a matter of debate.
One disease that's definitely evolving in animals is influenza. And one place it's evolving is none other than Guangdong, China, where animals are kept in close proximity to one another. Flu viruses tend to arise in ducks and geese. They spread to chickens and to pigs. Pigs can also get infected with human flu viruses, so they make a good mixing pot for new flu. When an animal or a person is infected with two different flu viruses, the viruses like to swap parts. Voilà! A new virus emerges.
Infectious disease specialists don't wonder whether there will be a new worldwide flu epidemic. They only wonder when it will happen. There have been two recent close calls.
In 1997, lethal bird flu arose in the poultry markets of Hong Kong. People got infected and died, but the slaughter of millions of chickens stopped the virus before it learned how to spread from person to person. In 2001 and 2002, similarly bird flu viruses evolved in Hong Kong chickens. Fortunately, they didn't spread to humans.
Robert G. Webster, PhD, is director of the World Health Organization collaborating center on influenza viruses in lower animals and birds.
"We don't want this in humans or the world will be in deep, deep trouble," Webster told WebMD in a 2002 interview. "What will you do if one of these gets away? You haven't got anything to do. Are we going to be prepared for this? It is going to happen sooner or later."