It's just one cow. But the ripple effects of a confirmed case of mad-cow disease in western Canada this week are myriad - falling stock prices of fast-food chains, the closing of US borders to Canadian beef imports, even perhaps a dip in economic growth rates.
They highlight, as did the SARS outbreak, how fear of disease in today's interconnected world can travel at fiber-optic speed - and can roil markets and wreak havoc on global trade and national economies.
Yet as serious as the threat is, experts insist there are strong reasons to counterbalance the concerns. Knowing how quickly plagues can spread, for instance, officials in many countries have erected barriers to mad-cow and other diseases.
Once news about a scourge gets out, countries can mobilize vast resources to stop their spread. When SARS hit, for instance, researchers in several countries scrambled to understand and halt it.
"When something new shows up and you don't know a lot about it, you're really scared," says George Gray, acting director of the Harvard Center for Risk Analysis, who led a 2001 study of US susceptibility to mad-cow disease. "But as we learn more, it tends to lessen our fears."
Dr. Gray notes that mad-cow disease is much harder to spread than many believe. It's also becoming clear that the human version of the plague is much less harmful than was thought. And both the US and Canada have strict measures in place to keep the disease from spreading.
Since 1997, it's been illegal in both countries to feed rendered bits of protein - cow parts, essentially - to animals. Eating tainted bits of brain or spinal cord seems to be the main way the disease spreads to other cows. It's not always clear how closely such laws are followed, of course. But even assuming some degree of noncompliance, the Harvard study found that in a hypothetical scenario in which 10 infected cows were imported, only about three new cases of BSE (short for bovine spongiform encephalopathy, the scientific term for mad cow disease) would occur.
"There were hundreds of thousands of cases in the UK, and we managed to keep it out - or at an extremely low level - in North America," says Gray.
Also this week, researchers in Britain revised their assessment of the disease's danger. Scientists at Imperial College in London had been projecting that the spread of Creutzfeldt-Jakob disease, the human form of mad cow, could cause several hundred thousand deaths over the next eight decades. They now suggest it might be closer to between 40 and 540.
The world has significant progress. "We can't reduce the risk to zero, but we seem to have come to the stage where people believe that we can control all the risks," says Kurt Klein, professor of economics at the University of Lethbridge in Alberta.
The case points up a paradox of the age of globalization - that both fear and resolve can mount quickly. "The trade in animals goes back to biblical times," says Stephen Kobrin, a globalization expert at the University of Pennsylvania. But today "There is instant awareness" of any problems. The news can spark widespread fear - and perhaps fewer trips to McDonald's by worried consumers. It can also quickly build political will - and mobilization of scientific and other resources - to protect the public.
Observers say the world has been largely successful at stopping the broad spread of SARS. The 1986 outbreak of mad-cow disease in Britain - which led to the destruction of 3.7 million animals - served as a warning to other nations.
Though this cow has been making big headlines, it's actually not the first to appear in North America. In 1993, there was another case in Canada, in a cow that had just been imported from Britain. In that instance, however, the source of infection had taken place overseas.
This time around, things are much less clear, and the Canadian Food Inspection Agency is devoting significant resources toward determining the source. They also emphasize that the animal was slaughtered back in January, that it didn't go into the food chain, and that the rest of the herd would now be slaughtered.
Officials on both sides of the border are waging war on public perception as much on the disease, even eating steak in public.
"I think they can get control over this disease," says Dr. Klein. "But will people actually eat beef afterwards? That's the main question."
• Larry Donovan in Edmonton, Alberta, contributed to this report.