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
"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."