Monday, 3 September 2012

Why cannibalism is bad

Um...because it's gross??

Well, yes. Unless you happen to be a zombie or a tadpole, cannibalism probably isn't something you'd ever consider doing. (Yes, tadpoles are cannibalistic. I've seen it. It's a little creepy.) But some people are cannibals. They don't kill people in order to eat them. There's no murder going on here. They eat parts of their already dead relatives, in order to absorb their spirit and power, and return their life force to the community. It's a form of mourning. But this custom has one very big, very deadly downside. Cannibalism is an excellent way to give yourself a brain disease.

A tadpole (well, technically a froglet) of the South African clawed toad. Cute, right? Sure, until you realize that their favorite snack is each other! From caudata.org.

Let's go back about 50 years. There was a tribe of people living in Papua New Guinea. They called themselves the Fore. And they had a problem. People were coming down with a terrible wasting sickness. They had difficulty moving, headaches, tremors, and difficulty speaking. They eventually lost the ability to coordinate their movements, and became unable to speak or respond to their surroundings. Everyone who had the disease died. The people called it kuru, which meant "shiver", after the uncoordinated, jerky muscle movements.

A doctor named Michael Alpers and an anthropologist named Shirley Lindenbaum visited the Fore, and they recognized the disease. It looked like a form of a very rare neurodegenerative disease called Creutzfeldt-Jakob Disease (CJD). ("Neurodegenerative" diseases are diseases where neurons die.) CJD is sometimes inherited, and sometimes people develop it randomly for unknown reasons. There's a third way it can be spread: by eating infected brains.

That's how it was spreading in the Fore. Most likely someone, sometime in the past, randomly developed the disease. When that person died, their relatives ate the brain, which to them was a sign of respect. Over the years, those relatives died. Their brains were eaten, and the disease spread. Since the time from infection to the first appearance of symptoms (known as the incubation period) is between 5 and 20 years, but can get as high as 50 years, not everyone who ate the brains died from kuru. No one connected cannibalism with the disease.

CJD and kuru are part of a family of diseases called the transmissible spongiform encephalopathies (pronounced en-sef-uh-lop-uh-thee). That's a mouthful, so I'm going to shorten it to TSEs. But that name essentially means, "diseases which make the brain look like a sponge". TSEs kill neurons, causing holes in the brain and creating the spongy appearance. They are caused by prions, which are infectious proteins. There is no cure.

You're probably already familiar with at least one prion disease. In the 1990s, a bunch of people in Britian got sick after eating beef. They had a terrible neurodegenerative disease, with symptoms a lot like kuru and CJD. After they died, their brains looked like sponges. Have you guessed the disease yet? The clue is the word "beef." This disease is called bovine spongiform encephalopathy. Also known as....MAD COW DISEASE.

Healthy brain tissue from a cow. From the FDA.

Brain tissue from a cow with mad cow disease. Note all the holes that make it look spongy. From the FDA.

In humans, TSEs usually exist as single, isolated, cases, not as epidemics. The mad cow disease epidemic happened because cow food came with added bits of cow, including cow brains. That's right...people were feeding cows to cows. It was cow cannibalism. So the prions from one or two sick cows quickly spread to lots of cows. Those cows were made into hamburgers, but the burgers were contaminated with the brains and spines of the cows. People who ate the contaminated burgers became infected with the prions, and got sick with mad cow disease.

Once we figured out what was going on, cow cannibalism became illegal. People are no longer allowed to feed cows to cows. There are also strict rules in place to prevent any brain tissue from getting into burgers. Thanks to these rules, there hasn't been another outbreak. But the British outbreak isn't over. Since the incubation period is so long - up to 50 years - it's likely that more people will develop symptoms over the next few decades.

Mad cow disease is EXTREMELY RARE!! Every time a cow is discovered with the disease, there's a world-wide media panic attack. Calm down everyone! It's not that bad! Yes, what happened in Great Britain was terrible, but we learned from it. There's lots of measures in place to prevent prions from getting in to food. The chances of new human cases are extremely small. So you can keep eating beef if you want. Just don't eat the brains.

Oh, and just in case you're wondering, the Fore people still live in Papua New Guinea, and they no longer eat each other's brains.

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