The United States is highly resistant to the introduction of bovine spongiform encephalopathy. And, even if the deadly disease were to enter this country, there is little chance of it becoming established. Those are the conclusions of a Harvard University study commissioned by the Department of Agriculture, assessing the effectiveness of current U.S. measures to guard against BSE.
The study, conducted over a three-year period by the Harvard Center for Risk Analysis, has been eagerly anticipated by government and industry alike. It credited early import prohibitions by the USDA on live ruminants and ruminant meat and bone from Europe, and a feed ban implemented by the Food and Drug Administration as being chiefly responsible for keeping BSE out of the country and for preventing its entrenchment.
"We found that even if BSE were ever introduced, it would not become established," said project director George Gray, PhD, acting director of the Harvard center. "With the government programs already in place, even accounting for imperfect compliance, the disease in the cattle herd would quickly die out, and the potential for people to be exposed to infected cattle parts that could transmit the disease is very low."
The USDA and Department of Health and Human Services welcomed the conclusions, released in late November. It "clearly shows that the years of early actions taken by the federal government to safeguard consumers have helped keep BSE from entering the United States," said Agriculture Secretary Ann Veneman.
"This is a reassuring finding," agreed Health and Human Services Secretary Tommy Thompson. Both Thompson and Veneman believe existing safeguards must continue to be improved.
Those sentiments were shared by the National Cattlemen's Beef Association, the largest representative of the nation's cattle farmers and ranchers. "Harvard's report is an important step in this country's ongoing efforts to continually evaluate and enhance the series of firewalls that have effectively protected U.S. cattle herds for more than 15 years," said association CEO Chuck Schroeder.
The study will be peer reviewed by a panel of outside experts to ensure its scientific integrity, according to Veneman.
Not long after BSE was first diagnosed in cattle in the United Kingdom in 1986, the British beef industry was nearly decimated. In Europe, about 100 people have died from a rare neurologic illness known as variant Creutzfeldt-Jakob disease. Many scientists believe the individuals contracted vCJD by eating neural tissue from BSE-infected cattle.
Only recently has the United Kingdom resumed a modest beef exportation program. Nonetheless, the disease has emerged in cattle across Europe and Asia. Sweden is the only European Union member without a reported case of BSE, whereas Japan identified its first infection last September.
To this day, the United States maintains its 1989 import ban on live ruminants from the UK. It was extended in 1997 to Europe. That same year, the FDA prohibited the use of most mammalian protein in the manufacture of animal feed intended for cows and other ruminants. As a result, BSE has not infected U.S. cattle.
Although BSE has not been detected in the United States during 12 years of active surveillance of high-risk animals, the Harvard study does not preclude the possibility the disease entered the country prior to the 1989 ban. Between 1980 and 1989, 334 animals entered the United States from the UK. They were imported as breed stock, not as beef or dairy production animals. Of those, 161 were disposed of in a manner that poses no risk to humans or other animals. The same cannot be said for the remaining 173 animals, however.
The Harvard analysts go on to say there is more than an 80 percent chance that these animals did not expose U.S. cattle to BSE. Furthermore, if the U.S. animals were exposed, there is a significant chance it resulted in no new cases of the disease. If infection did occur, the number of cases would be too small to detect, according to the study. For instance, the import of one sick animal, on average, yields less than one new BSE case in 20 years. But by then, government and industry measures implemented during the past five years will have stopped contagion and begun eradicating it.
The federal government believes existing safeguards
against bovine spongiform encephalopathy must
There also appears to potential for a BSE outbreak caused by scrapie, chronic wasting disease, or other cross-species transmission of similar diseases found in the United States. The Harvard study found that naturally occurring BSE infections would cause only one to two cases annually, with little spread. If an outbreak of BSE were to occur, it would most likely be eliminated within 20 years after its introduction.
The analysts conclude that only a small amount of potentially dangerous tissues would reach the human food supply and be available for possible consumption. BSE expert Dr. William D. Hueston, director of the Center for Animal Health and Food Safety at the University of Minnesota College of Veterinary Medicine, said the Harvard study "does not appear to be sugar-coated." It acknowledges the possibility that BSE could have entered the country, takes into account the chance of spontaneous infections, and examines the potential for human exposure.
The mathematic model used by the analysts allows for consideration of a broad range of potential scenarios, Dr. Hueston said, adding that the greatest benefit of the study is the process of risk assessment itself. "Identifying weaknesses in the prevention system and potential scenarios in which BSE might enter the U.S. helps strengthen the country's defense," he said.
On the basis of study recommendations, the USDA announced in November a series of initiatives to strengthen existing safeguards. BSE tests on cattle will be more than doubled this year, with an estimated 12,500 samples targeted, up from 5,000 in 2001. A number of new regulatory actions will be considered, including prohibiting the use of the brain and spinal cord from certain categories of animals in human food, as well as the use of certain stunning devices for immobilizing cattle during slaughter.
The Harvard study can be viewed at www.usda.gov.