Monday, April 28, 2003

BSE, Scrapie, Creutzfeldt-Jakob, Kuru:

Seeing my skull so prominently each day made me somewhat sensistive to a Science article (v. 300, Iss. 5619, pp. 640-643; 10.1126/science.1083320) about cannibalism and the presence of prions in brain matter.

The recent mad cow scare in Europe, and the ongoing struggle with similar diseases in sheep ("scrapie") has been linked to the use of animal matter in making feed for the same animals. In essence, an undetected infected animal is slaughtered and used to make feed for other animals, and the infection is passed on because prions can survive food processing cycles. This process is actually quite common - the part of animals that are not used for human consumption end up in the food chain for our pets and also back to feed the animals themselves. Sheep and cows often end up eating highly processed sheep and cows in their feed. They are unwitting cannibals. The mad cow scare came about precisely because brains from infected cows were used in the processing of food for human consumption -- and unlike bacteria, which can be killed or at least controlled by careful preparation and cooking, prions are not affected. A well-done hamburger could carry active prions.

Cannibalism among humans is now rare. However, it has not always been so, and prions were passed on and infection rates among groups practicing cannibalism reflected this. In New Guinea, where cannibalism was practiced until the 1950's, there are still many cases of kuru, a prion similar to CJD, among a group called the Fore. The Science article points out the interesting fact that there is a genetic trait that can confer protection against infection, and that this trait is prominent in the Fore, as we might expect. The surprising point was that when this trait is looked at among other groups worldwide, the most likely explanation for the observed distribution is that human cannibalism was once a widespread practice.

I am not clear on the transmission mechanism of prions in other animals, like deer, moose, antelope etc. that are known to suffer from them. These animals are not known to consume their dead, so there must be another form of transmission for the prions in these cases, which may also be valid for the cases with cows, sheep and humans.

For dinner tonight: Blackened hamburger. Carbonized. Irradiated.