Small Study of Macaques and BSE Suggests Low Transmission Risk

British medical journal, The Lancet, published the results of a small-scale French study into the transmissibility of bovine spongiform encephalopathy (BSE). The results confirm what the evidence and computer models have already implied — that the risk of transmission of BSE from animals to humans in the form of vCJD is very low. The small size of the study, however, do limit the ability to extrapolate from the study.

Researchers took two adult macaque monkeys and exposed them to five grams of brain tissue from a BSE-infected cow. After five years, one of the macaques developed symptoms of a vCJD-like disease while the other macaque remains health and symptom-free.

The French researchers suggest that in order to have a sizable risk of infection, and individual would have to eat about 3.3 pounds of meat from an infected cow. Since current slaughterhouse regulations in the UK and elsewhere are able to detect BSE-infected meat when it hits a threshhold slight less than that from an infected cow, the French research suggests that such existing regulations are well tuned to prevent further such infections.

The researchers also suggest that the incubation period for BSE in humans could be, on average, greater than 50 years, which would explain why so few people have died from vCJD despite presumably widespread exposure to BSE-infected beef in the UK. Other studies have suggested that the vCJD incubation period may, on average, be significantly longer than current human lifespans.

The vCJD epidemic appears to have peaked in Great Britain. Where 18 people died from vCJD in 2003, only 9 people succumbed to the disease in 2004 and there are only five additional suspected cases of the disease in Great Britain.

Sources:

Study optimism on mad-cow disease. News.Com.Au, January 27, 2005.

Risk of oral infection with bovine spongiform encephalopathy agent in primates. Corinne Ida Lasmézas, et al., The Lancet, January 27, 2005.

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