Another four imported cows are quarantined in Vermont. Both European and U.S. experts believe BSE was created in the 1980s in the U.K. when parts of scrapie-infected sheep were rendered into meat and bone meal and fed to cows. Although this practice was old, solvents considered health risks to rendering plant workers were banned in the 1980s, and lower temperatures were used to process the feed. Experts suspect the new methods allowed the disease to survive and to emerge in cattle in a new form that affects the central nervous system of cattle. Infected cattle carcasses in turn were used as protein supplements in cattle feed, spreading the cattle-adapted disease.
Incubation is thought to range from three, to eight years.
Incubation is thought to range from eight, to 20 years. In March, the U.K. Department of Health reported a total of 85 confirmed nvCJD cases and 10 probable cases, five of whom still are alive. Only a handful of cases exist outside the U.K. Confirmation of the disease is possible only during an autopsy after death. However, depending on assumptions about the incubation period and other variables, experts said the extent of the human outbreak could range from fewer than 100, to hundreds of thousands of cases. They cautioned that the possibility that large numbers of apparently healthy persons might be incubating the disease, coupled with unknowns about the disease, raises concerns about blood and organ donations, surgery and medical diagnostic procedures.