Apr 28, 2006 (CIDRAP News) After close to 2 years of expanded testing, the US government is estimating that there are between four and seven cases of bovine spongiform encephalopathy (BSE) among the nation's 42 million adult cattle.
"The data shows that the prevalence of BSE in the United States is extraordinarily low," US Department of Agriculture (USDA) Secretary Mike Johanns said at a teleconference this morning.
The estimate is based on testing of about 730,000 cattle since 1999, including 690,000 since June 2004, Johanns reported. The testing program was greatly expanded after the country's first BSE case was found in a Canadian-born cow in December 2003. Two more cases, both in US-born cattle, have turned up since then.
The USDA is looking to cut back the BSE testing program, but it will wait for an independent scientific review of the prevalence estimate, Johanns said. The agency hopes the review will be completed by the end of May.
USDA used two methods to estimate BSE prevalence. The "BSurvE" method yielded an estimate of seven cases, while the "Bayesian birth cohort" method indicated four cases, according to the agency's draft report.
The estimates did not factor in the first BSE case, since that was in a Canadian-born cow. With the inclusion of that case, the respective estimates were 11 and 5 cases.
The agency ran several additional sets of calculations to assess the effect of changing certain assumptions and to see what the estimates would be if up to three more BSE cases had been found. The resulting estimates ranged from 1 to 30 cases, and "strongly support the conclusion that the prevalence of BSE in the United States is below 1 case per million adult cattle," the USDA report says.
"Science enables us to set a 95 percent confidence level in that estimate," Johanns said. "In other words, we have an extraordinarily healthy herd of cattle in our country."
Johanns stressed that the BSE surveillance program "is not part of our food safety protection." The surveillance is designed to gather enough data to draw statistically valid conclusions about the prevalence of BSE, he said. Food safety, on the other hand, is ensured by the ban on use of nonambulatory cattle and high-risk cattle parts (specified-risk materials) in human food and the ban on feeding cattle protein to cattle, he added.
USDA officials refused to predict exactly how many cattle will be tested for BSE in the future, but they said the number is likely to be somewhere in the neighborhood of 40,000 per year, far below the level of the past 2 years.
"I would argue that there's little justification for continuing surveillance at this [expanded] level once our analysis is affirmed by peer review," Johanns said.
Dr. Ron DeHaven, administrator of the Food Safety and Inspection Service (FSIS), said the World Organization for Animal Health (OIE) has two sets of guidelines for BSE testing: one for initially determining the prevalence of the disease and another for "maintenance" surveillance. USDA will meet or exceed the recommended level of maintenance testing, he said.
"Based on the current evaluation we estimate that number will be somewhere in the 40,000 animals per year level," DeHaven said.
In response to questions, DeHaven said the USDA is currently testing 5,000 to 7,000 cattle per week at a cost of roughly $1 million weekly.
The prevalence estimate comes as the USDA continues to negotiate for reopening of the Japanese market to US beef. Japan banned US beef after the first BSE case was found in 2003. The ban ended in December 2005, but it was renewed in January of this year when some pieces of bone were found in veal imported from the United States.
Johanns said he plans to share the prevalence estimates with Japanese agriculture minister Shoichi Nakagawa next week in Geneva and to explain the process for deciding on future surveillance. "I think he'll be very, very pleased to see it [the analysis]," Johanns said.