July 19, 2001 (Washington) -- Although no cases of mad cow disease or its human equivalent have ever been reported in the U.S., the government surveillance system to detect infected cattle is inadequate and varies widely from state to state, the consumer advocacy group Public Citizen charges in a new report.
One method the U.S. Department of Agriculture has implemented to catch an outbreak of mad cow disease -- also known as bovine spongiform encephalopathy or BSE -- is to slaughter and autopsy the brains of cattle that display symptoms suggesting that they may have contracted the disease.
This is important because it is believed that eating products made from cattle infected with the mysterious proteins that cause mad cow disease, called prions, can lead to the human equivalent of the disease called variant Creutzfeldt-Jakob disease, or vCJD, which leads to the degeneration of the brain.
It is believed that an outbreak of mad cow disease in Europe that began in the 1980s has led to the infection of more than 100 people in that region, primarily in the U.K. At present, there is no cure for vCJD, and most of the Europeans inflicted with vCJD have already died.
Public Citizen reviewed the USDA surveillance records in the U.S. and found "enormous variations in the BSE testing rates between states," which suggest "that the USDA's testing program is being administered in a haphazard fashion," the group says in their report.
The states with the highest rates of testing had rates that were 400 to 2,000 times those of the lowest states. This makes the USDA's claim that no cows with mad cow disease have been detected in this country "not very compelling," Public Citizen says.
Public Citizen wants the USDA to modify its surveillance system to reduce the variability between states and make the rate of testing more uniform, Peter Lurie, MD, deputy director of the organization's Health Research Group, tells WebMD. "You want to have the same likelihood of finding a positive cow no matter where it occurs."
The USDA "needs to start to take some sort of corrective action in the low states," Lurie says.
But Linda Detwiler, DVM, counters Public Citizen's charges by saying that the variability between states is deliberate because the USDA targets its testing on animals that are most likely to have mad cow disease. Detwiler is a senior staff veterinarian with the USDA.
These include older cattle and dairy cattle, and these types of animals are not distributed evenly across the country, Detwiler tells WebMD. So variability from state to state is to be expected.
Shu Chen, PhD, director of protein analysis at the National Prion Disease Pathology Surveillance Center, which monitors the possible occurrence of a case of vCJD in the U.S., concurs with Public Citizen's view that the USDA's surveillance is inadequate and needs to be strengthened.
"More rigorous surveillance is needed ... so we won't regret it later on," Chen tells WebMD, referring to the potential for mad cow disease to make its way into the food supply and infect humans.
Chen points out that "Germany and Italy claimed that they didn't have BSE but when they looked hard and did more rigorous testing," they found that they did have cases of mad cow disease.
But he notes that even if mad cow disease is detected, it does not necessarily mean that cases of vCJD will be found. This is because it depends on whether the disease made it into the food supply and the extent of human exposure.
The USDA plans to increase its rate of surveillance from about 2,500 to 5,000 animals per year, Detwiler says. At this rate, the agency could detect an outbreak of mad cow disease that involved as few as 59 cattle among the 99 to 100 million cattle in the U.S.
She concedes that the agency could be doing more surveillance and that "we have requested funds for additional surveillance."
But Detwiler says the surveillance system, along with the ban on the importation of cattle, goats, and sheep from countries known to have cases of mad cow disease and the FDA's ban on ingredients in cattle feed that may cause mad cow disease, combine to provide a reasonable assurance that an outbreak in the U.S. will be prevented -- or at least detected early on.
In addition, the USDA has contracted with the Harvard School of Public Health to conduct an independent review of the agency's system for detecting and preventing mad cow disease to identify areas where the agency might improve. That report is expected soon, Detwiler says.