Nobel laureate Dr. Stanley Prusiner delivered the third Annual Gairdner Public Lecture, “Mad Cows and Dementia in People: A New World Biology,” at the St. Lawrence Center on Friday. Prusiner was the first scientist to propose that proteins, not just viruses, can be infectious agents. In so doing he revolutionized the field of neurobiology.
Prusiner began his lecture with a photo of the Russian ballet choreographer George Balanchine, who died of Creutzfeldt-Jakob disease (CJD) in 1983, the most famous person to ever die of the disease. CJD is the human equivalent of bovine spongiform encephalopathy (BSE), or mad cow diseasea chronic, degenerative disorder that affects the central nervous system in cows. Both CJD and BSE are diseases transmitted by infectious proteins called prions.
Prions are unlike viruses, as they do not possess a genome. “Prions are different from viruses in that their synthesis is directed by proteins, not by DNA,” says Prusiner.
Prusiner showed an example of massive vacuoles, or air sacs, in the brains of individuals with CJD, which is characteristic of the disease. “There is clearly a disregulation of ion and water in the brain,” Prusiner said. Post-mortem biopsies reveal that these brains contain massive amounts of prions. The neurodegeneration causes individuals with CJD to lose their motor control and mental abilities.
There are several prion diseases such as scrapie, found in sheep, chronic wasting disease in deer and elk, and kuru, a disease that affected some indigenous people in New Guinea. Until the late 1950s, some tribes practiced ritualistic cannibalism by eating their dead relatives’ brains. But incidents of the disease have decreased over the years following the ban of the practice.
Prusiner says the cause of scrapie among sheep is still unclear. However, once sheep are infected, there is “horizontal spread of the disease” within the herd. When cows consume meat-based animal feed containing infected sheep, they contract BSE. The disease then moves its way up the food chain when humans consume beef from infected cows.
The first case of bovine spongiform encephalopathy BSE in Canada occurred in 1993, diagnosed in a cow imported from Britain. The second case occurred in May of this year.
A member of the audience asked whether we could contract prion diseases by consuming non-beef meat products. Prusiner explained, “In order for the protein to be transmissible, the gene product needs to be relatively similar.” Eating chicken, for example, is relatively safe, since the prions of birds cannot be transmitted to us. Likewise, eating fish is relatively safe, since “genes in fish are extraordinarily distant from ours.”
Throughout the lecture, Prusiner brought attention to the lack of government testing. He is especially critical of the U.S., which, despite being the richest country on the planet, is not willing to spend money on tests of slaughtered cows. He believes that tests should be done on every cow slaughtered. It is precisely because no such thorough testing has ever taken place that nobody knows how many cows have BSE. Prusiner emphasizes,
“We need to have an idea of the numbers.”
Canada also refuses to institute this sort of testing regime. In Japan, as Prusiner points out, every single cow slaughtered is tested for the disease.
