How Animals Transmit Disease to Humans

June 10, 2003 -- The Midwestern prairie dog is not a common pet. But some pet stores have been selling them, along with exotic animals from around the world.

Investigators say that is why more than 30 people today are suspected of having a smallpox-like disease that has never been seen before in this country.

"This is a virus that we simply don't have a lot of information about," Dr. Steve Ostroff of the Centers for Disease Control and Prevention told a news conference Monday.

The virus is called monkeypox, though the name is misleading.

Though it was first observed in African monkeys in 1958, it was probably carried here fairly recently by one exotic rodent — a giant Gambian rat — flown to the United States to be sold as a pet.

The rat in turn infected prairie dogs owned by a pet dealer.

Doctors believe people got sick from handling the prairie dogs.

"I think it's very important that we keep our guard up in terms of watching for cases," said Ostroff, "both over the short term as well as the longer term."

Most ‘Emerging Diseases’ Come From Animals

This case illustrates something that doctors have long known — that animal diseases probably cause most of the microbes that infect human beings. A Scottish study reported that 61 percent of human infectious diseases originated with animals, as do 75 percent of all "emerging diseases" — the ones that have appeared recently.

Some examples:

The first human AIDS cases may have been transferred from chimpanzees.

West Nile virus moved from birds to mosquitoes to people. It is now found in 44 states.

SARS, sudden acute respiratory syndrome, may have come from civets, a breed of wild cat, in China's Guangdong province.

Even measles may have been transmitted from animals 5,000 years ago.

"Remember, we're not the dominant life form on Earth," said Dr. Daniel Shapiro, an associate professor of medicine at Boston University. "Bacteria and other infectious agents are, really.

"Because this is novel, it's something we haven't really heard about," said Shapiro. "For a lot of people this is very, very scary."

The good news, says the CDC, is that monkeypox does not seem to be terribly dangerous or very efficient at passing from one person to another. All the suspected victims so far came in direct contact with infected animals, and in some cases were bitten by them.

The bad news is that in a global economy with a growing population, it is getting easier and easier for exotic diseases to travel great distances.