Mad-Cow Variant Poses Low Risk

San Jose Mercury News (CA)

April 26, 2012

California’s first case of mad-cow disease was caused by a rare and poorly understood variant of the illness, but what is known is it’s not nearly as threatening as the infection that decimated British cattle herds in the 1980s and 1990s, and sickened more than 220 people with a deadly brain disease.

Experts said Wednesday they consider the risk to humans from this type of the disease extremely low. No human cases have ever been detected. And in cattle, the variant has never been seen in the United States until now and is not easily transmitted.

Consumers remained calm Wednesday as the investigation widened. Scientists scrutinized infected tissue at an Iowa lab, and epidemiologists studied the Tulare County dairy where the 5-year-old cow lived. Researchers believe the unique version of bovine spongiform encephalopathy revealed this week occurs sporadically in older animals when cells go awry rather than spreading widely through infected feed.

“It behaves differently” than the typical form of the disease, said Pierluigi Gambetti, a pathologist who specializes in mad-cow disease research. When an infection is spread through feed, clusters of cattle get sick, he added. “This is random, here or there not small epidemics.”

On Wednesday, the U.S. Department of Agriculture stepped up its search for other infected cows but said it would take time to complete the investigation.

Random testing

Although infectious, the variant known as “atypical L-type BSE” has not been linked to human deaths. It’s the first new case of the disease in the United States since 2006 and the fourth ever discovered in the country.

“There is no evidence that this atypical form has ever been transmitted to humans,” said Gambetti, a professor at Case Western Reserve University in Cleveland. That may be because it is rare, and any infected meat is diluted when mixed with other meat, he added.

The typical form of mad-cow disease is now believed to be largely under control due to a ban on meat and bone meal in livestock feed and the removal of risk materials from the food chain. But the previously unknown, atypical versions of mad-cow disease are raising new questions.

They were discovered only because of wide-scale testing. Mad-cow disease was initially assumed to have a single cause. But massive testing of slaughtered animals—particularly in Europe and Japan—revealed two other variants. In addition to the L type, there was an H type found several years ago in a cow in Arkansas.

Similar testing discovered this week’s California case. The cow had been collected by a renderer, and the disease was discovered in random testing. Although old dairy cows are used to make hamburger, this one was not destined for the food supply, officials said.

“It was inevitable,” said neurologist Richard Johnson of Johns Hopkins University, a consultant on mad-cow-like diseases to the National Institutes on Health. “I assumed it would eventually occur. My own suspicion is that it is an endemic agent” contained within aging cow populations.

The test was performed when the animal was brought to a transfer facility for a processing plant near Hanford, in the heart of California’s dairy country. According to the Associated Press, a plant official said the cow hadn’t exhibited outward symptoms of the disease: unsteadiness, a drastic change in behavior or low milk production.

But when it arrived at the facility with a truckload of other dead cows, it met the criteria for government testing: older than 30 months and a fresh corpse. “We randomly pick a number of samples throughout the year, and this just happened to be one that we randomly sampled,” Dennis Luckey, executive vice president of Baker Commodities, told the Associated Press.

The samples went to the food safety lab at UC-Davis. By April 19, markers indicated the cow could have bovine spongiform encephalopathy. The samples were sent to an Agriculture Department lab in Iowa for further testing, where the variant was identified.

Still ordering burgers

On Tuesday, U.S. Department of Agriculture officials arrived at the unidentified farm to investigate “all factors that might have contributed,” as well as other animals, said Jere Dick, veterinarian and associate deputy administrator with USDA Veterinary Services.

On Wednesday, a major South Korean retailer suspended sales of U.S. beef. But live cattle futures, which dropped Tuesday, recovered as it became clearer that exports would not take a significant hit. Meanwhile, diners seemed largely unperturbed by the news.

At Henry’s World Famous Hi-Life steakhouse in San Jose, regular customer Ken Ruff was enjoying a steak and baked potato at noon Wednesday. He said he was in Europe during a deadly outbreak of the disease there. “But I’m not worried here,” the construction superintendent said. “They’ve taken the right precautions.”

A few blocks away at Peggy Sue’s restaurant at San Pedro Square, Solly Hernandez had just ordered the house specialty cheeseburger. “I’m not scared because they said that cow was not going to be sold on the market for people,” the stay-at-home mother from San Jose said.

In Pleasanton, most of the customers leaving a Safeway weren’t worried. “Until I hear more (cases), I would still be OK buying it,” Marla Hunken said.

Research suggests these atypical variants occur when aging cells make the wrong proteins. The infection does not spread from cow-to-cow contact. It also is not a genetic mutation, so it’s not passed down from cow to calf. In Japan, where the atypical cases are counted, the numbers are very low. Rates are not known in the United States.

Despite the rarity, it poses a theoretical risk to humans. Studies show that primates and transgenic mice get brain disease when fed the L-type variant, so humans could be infected as well. That’s why scientists urge continued testing for all variants of mad-cow disease despite the low risk.

“The disease is so rare, the chances that someone would get the disease from an infected cow, whose meat is mixed with millions of other cows, is not expected,” Gambetti said. “There is a tremendous dilution effect. The fact that it was found is quite remarkable.”