In the 1990s beef from the United Kingdom and several other countries was banned worldwide because of fears of bovine spongiform encephalopathy (BSE), a contagious progressive neurological disorder of cattle that is part of a group of diseases called transmissible spongiform encephalopathies, or TSEs. The disease results in dementia, uncoordinated movements, and other brain-related difﬁculties and therefore has become known as mad cow disease.
Rather than a traditional virus or bacterium, the culprit in TSEs is an abnormal form of a cell-surface protein, called a prion. The damaged prions are able to cause other proteins of the same type to change their shapes as well, and the misshapen protein molecules clump together and accumulate in brain tissue, much like the plaques characteristic of Alzheimer’s disease.
The outbreak in the United Kingdom was serious, with more than 183,000 conﬁrmed cases of BSE occurring in more than 35,000 herds by the end of November 2003. The outbreak has been widely attributed to the unnatural feeding methods that the worldwide demand for increased beef production has generated. Mad cow disease may be the result of cattle, which are herbivores in nature, being fed meat-and-bone meal derived from sheep. The problem was made far worse by feeding bovine meat-and-bone meal made from infected cattle to calves, essentially creating a population of cannibalistic cattle.
This is reminiscent of the spread of a similar disease in a human population earlier in the twentieth century. Kuru, a rare and fatal brain disorder also transmitted by prions, spread to epidemic levels during the 1950s and into the 1960s among the Fore people in the highlands of New Guinea. The disease was transmitted via ritualistic cannibalism among the Fore. In their funeral rites, relatives prepared and consumed the bodies, including the brain, of deceased family members. As with other TSEs, brain tissue of kuru victims was highly infectious, and kuru was also transmitted through contact with open sores and wounds. Kuru primarily affects the cerebellum, and so the early symptoms involved poor movement control. Victims would eventually become comatose and die within six months to a year of the ﬁrst appearance of symptoms. Unlike the other TSEs, kuru does not appear to produce dementia. There is neither a cure nor any effective treatment for kuru—the only way to avoid it is to avoid cannibalism. The government of New Guinea began to actively discourage cannibalism in the 1960s, and the disease has now largely disappeared.
The main reason for the panic over the bovine disease is a concern that it may be possible for humans to develop a similar disease, Creutzfeldt-Jakob disease, through contact with infected meat. Evidence is strong that BSE can be transmitted to humans, where it develops into a variant form of Creutzfeldt-Jakob disease (called vCJD). As of December 2003, 143 cases of vCJD due to BSE exposure had been conﬁrmed in the United Kingdom alone, but the beef supply in the United States appears to be completely safe, even though one case of BSE was identiﬁed in Oregon in 2003, in a cow purchased from Canada. This resulted in a temporary U.S. ban on Canadian beef, and no further cases have been reported here. We probably feel safer than we should at the moment, however, since the TSEs can have a very long incubation period. In the case of kuru, it was sometimes years or even decades after exposure that symptoms ﬁnally appeared.
- Klitzman, R. The Trembling Mountain: A Personal Account of Kuru, Cannibals, and Mad Cow Disease. Boulder, CO: Perseus, 1998;
- Yam, P. The Pathological Protein: Mad Cow, Chronic Wasting, and Other Deadly Prion Diseases. New York: Copernicus Books, 2003.