A day after the fourth-ever U.S. case of mad cow disease was confirmed in a California dairy cow, officials are characterizing it as an example of effective inspections, but from other reports it sounds like it was basically a lucky break. To some extent, both angles are true. But as only two South Korean retailers have so far canceled U.S. beef orders, compared with the multitude of nations that halted imports in 2003, it sounds like the rest of the world is tentatively going with the first scenario, to the relief of U.S. trade officials.

As Bloomberg's Rudy Ruitenberg reports, the discovery "shouldn’t affect the U.S. status of 'controlled risk' for BSE, the Paris-based intergovernmental animal health group, known by its French acronym OIE, wrote in an e-mailed statement today." The U.N. Food and Agriculture Organization's chief veterinary officer, Juan Lubroth, said: "The fact that the U.S. picked it up before it entered the food chain and the fact that they were transparent should give more confidence to the trading partners, not less." And of course USDA chief veterinarian John Clifford says he's confident in U.S. cattle: "USDA remains confident in the health of the national herd and the safety of beef and dairy products."

But this cow could easily have gone undiagnosed, because the U.S. does not exhaustively test every cow carcass for bovine spongiform encephalopathy. The cow in question showed no signs of the disease, and was only inspected through an "Agriculture Department surveillance program that tests about 40,000 cows a year for the fatal brain disease," the Associated Press reported. "We randomly pick a number of samples throughout the year, and this just happened to be one that we randomly sampled," Dennis Luckey, the vice president of Baker Commodities, which owns the rendering plant where the cow was found, told the AP for a different report.

The BSE in this particular cow came from a random mutation, The Guardian reported. "Random genetic mutations happen all the time in nature, so once in a while a cow will be born with a mutation that makes the BSE prion." The cow wasn't even presented for slaughter, so it never threatened the food supply, Clifford stressed.

Still, the testing could be more stringent. In 2003, Dr. Stanley Prusiner, the scientist who first discovered BSE, argued that "this nation should immediately start testing every cow that shows signs of illness and eventually every single cow upon slaughter... Japan has such a program and is finding the disease in young asymptomatic animals." But James Culler, a scientist at University of California, Davis, where the infected tissue was diagnosed, said the current level of risk is acceptable. "Are you worried about all of the meteors that passed the earth last night while you were sleeping? Of course not," he told the AP. "Would you pay 90 percent of your salaries to set up all of the observatories on earth to watch for them? Of course not. It's the same thing."