Suddenly, eating a hamburger seems almost as reckless as skydiving with a garage-sale parachute.

Federal officials insist American beef is safe, but the nation's first mad-cow case has left many people skeptical of government safeguards and worried that a mouthful of meatloaf today could prove fatal in 10 years.

In Washington and Oregon, where beef from the infected cow was processed, sold and almost certainly eaten, those concerns are magnified.

"You're the ones who are thinking: 'Whoa. The mad cow is right up the road, and it could be on my plate,' " said David Ropeik of the Harvard Center for Risk Analysis in Cambridge, Mass.

While the anxiety is understandable, the numbers tell a different story.

"Even for people in Washington, the risk is probably zero or as close to zero as scientists ever dare say," Ropeik said.

As many as a million cows were infected with the disease during the epidemic that started in England in 1986, and tens of thousands of people ate tainted meat. The first human cases were confirmed in 1996, but the death toll did not exceed 130.

"It's tragic and sad, but pretty good odds," Ropeik said. "And that was without controls like we have now, to keep brain and spinal cords out of the food supply."

With those controls in place — and only a single, confirmed cow infection — the chances that anyone will become infected are vanishingly small.

But Ropeik concedes statistics and expert assurances may not be very comforting to people facing a frightening and mysterious new threat.

Mad-cow disease is eerie in comparison to the viral or bacterial ailments people are used to dealing with. Caused by misshapen proteins called prions, it can't be cured or treated. The prions are impervious to cooking and irradiation. Scientists even tried killing them in boiling acid without success.

The disease gnaws holes in victims' brains, turning the tissue spongy and accounting for the scientific name, bovine spongiform encephalopathy. In humans, it robs memories, destroys reason and leads to coma and death.

"It's a really dreadful way to die," Ropeik said. "The scarier and nastier things are, the more we fear them. That's why we're more afraid of shark attack than heart attack."

Jim Boegl, of Bainbridge Island, said he realizes there's little chance he'll get sick. "The possibility of things making their way to me is pretty remote," he said yesterday. But like many people, he's still uneasy. "I'll probably be looking harder at chicken for the next few weeks."

Scientists always couch their risk assessments with the caveat: "based on what we know now." The many unknowns about mad cow add to the sense of dread, which is compounded by the fact that the disease is always fatal.

Those uncertainties should inspire greater concern, both by individuals and the government, says John Stauber, co-author of "Mad Cow USA."

"Having government and industry officials stand up and minimize the risk is scientifically absurd," he said. "We don't know what the risks are because until 1996, nobody had seen an individual suffering from this disease."

The human form of the disease, called variant Creutzfeldt-Jacob disease, takes 10 to 40 years to show symptoms, so many more people may be infected, Stauber said. Some experts in England estimate there will eventually be 100,000 human cases as a result of the epidemic there.

History is replete with examples of officialdom pooh-poohing the risks of chemicals, radiation and disease, and mad cow is another example, Stauber thinks. For nearly a decade, British officials assured the public that mad cow couldn't be transmitted to people.

Mistrust of government fuels fear, Ropeik said. "If we don't trust our government when they say they'll keep us safe, then all of the risk numbers and all of the science won't matter."

Though USDA officials acted quickly when the first laboratory tests came back positive, the agency's credibility has been attacked by critics who accuse it of lax regulation and inadequate testing. Revelations that sick animals are routinely used for food and that meat processed in automated meat-strippers can be contaminated with bits of diseased spinal cord were shocking to many in the public.

Peggy Massey, of Puyallup, said she plans to eat a lot less beef, largely because she thinks the federal government isn't vigilant in testing for mad cow and enforcing a ban on the use of animal products in cattle feed, the main transmission route for infection.

"They haven't laid down strict enough rules and penalties severe enough to control what's going on," she said. "The number of tests they've made is tiny compared to the number of cattle that are processed."

Ropeik says the USDA has done a credible job getting out facts about the mad-cow case. A careful review of those facts should be reassuring to people who wonder whether the meatballs they served last week were contaminated, he says.

USDA officials have been trying to track about 10,000 pounds of beef from the infected cow and 19 other animals slaughtered at the same time. About a quarter of the meat from one processor hadn't been distributed yet, but much of the rest may have already been eaten, including shipments to several small Asian and Mexican markets in Washington, Oregon, California and Nevada.

Officials say they are recalling the meat out of an "abundance of caution," not because they believe it dangerous.

The animal's spinal cord and brain, where the infection concentrates, were cut away by hand at the slaughterhouse. No automated equipment was used to strip meat from the backbone, eliminating the risk of nerve-tissue contamination.

The preponderance of scientific evidence suggests that beef muscle, which in this case was ground into hamburger, does not carry the disease. So even if somebody ate the meat, there's almost no chance of getting sick, said Jim Cullor, director of the University of California, Davis, veterinary-research center in Tulare.

The "almost" qualifier reflects evidence the infectious agent is found in blood. Recent studies have also found it in mouse muscle, though Cullor says that's not a cause for concern.

"With all due respect, a mouse is not a cow. A mouse is not a human, and none of us eat mice."

And for those who still wonder what the chances are they took home some of the 10,000 pounds of recalled beef, consider this: During the week of Dec. 14, when the meat might have been on sale, Washington residents consumed about 7 million pounds of beef, according to statistics from the American Meat Institute.

The experience in England shows that mad cow isn't highly infectious even among cattle, Cullor said. While many millions of cows there ate feed made from infected animals, the majority did not pick up the disease.

The U.S. has banned use of most animal products in cattle feed since 1997.

If there are more infected animals in the United States, the risks to the public will grow — but not significantly, Ropeik said. In an analysis for the USDA, he calculated what would happen under several scenarios, including the worst case: 500 infected animals and only 75 percent compliance with the feed ban.

The result: The disease would never spread far and would die out in cattle within two decades. During that time, the risk to people would remain minuscule because of all the existing safeguards.

It's lower than the risk, he said, of getting struck by lighting or drowning in the bathtub.

But would he be willing to eat meat from the infected Washington cow?

"Only if I was starving," he said. "It's a very low risk, but why take it?"

Seattle Times staff reporters Sara Jean Green and Vu Nguyen contributed to this report. Sandi Doughton: 206-464-2491 or sdoughton@seattletimes.com