Prions and Future Epidemics

Considering that I've eaten my fair share of British beef (I lived in England for a few years, and had a soft spot for the hamburgers at my local gastropub), this study was not welcome news. Here is the NY Times nut graf:

The long lives that some former cannibals enjoy before succumbing to a brain-wasting disease suggest that many more humans will eventually die of mad cow disease, scientists said Thursday.

The scientists arrived at their unsettling conclusion by studying the Fore tribe, who used to honor their dead by butchering them, eating their flesh, and smearing themselves with their brain tissue. But cannibalism is a bad idea for many reasons, and the Fore were almost wiped out by kuru, a prion disease transmitted by infected nervous systems (much like mad-cow disease.) What these scientists found was that kuru could incubate for as long as 56 years before killing its victim. The bad prions just quietly lurked in their head, waiting to convert their healthy tissue over to the dark side.

As always with prions, this study is controversial. The only thing we know for sure about prions is that we don't know very much. After all, some scientists now think that prion-like proteins are essential for long term memory...

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How long can an idea stay tantalizing? Back in 2003, I blogged about an experiment that suggested, incredibly enough, that our long-term memories are encoded by prions the misfolded proteins that are generally accepted to be the cause of mad cow disease. The evidence came from studies of a protein…
National Library of Medicine / Hot Medical News This silent film clip shows several victims of a disease called kuru. They are - or rather were - members of the South Fore, a tribe of approximately 8,000 people who inhabit the Okapa subdistrict of the Eastern Highlands Province of Papua New…
Cannibalism is a controversial topic. It is routine for particular societies to accuse "barbarians", enemies, or evil mythological figures, of cannibalism. When it comes to the archaeological record some skeptics have claimed that like "sacred objects" too often human remains found in peculiar…
People make terrible jokes about "mad cow" disease. ("Why is PMS called PMS? Because mad cow was already taken.") Pundits use it as an example of an over-hyped disease (and to be fair, estimates of total cases due to the consumption of contaminated beef in the UK have varied widely, ranging…

The Lancet article makes a good deal of sense. Several implications strike me. First, was the source case a spontaneous presentation of CJD, subsequently amplified by ritual cannibalism? That is a plausible cause, and fits with the hypothesis that BSE was also of spontaneous origin, amplified by the endocanibalism of cattle fed meat and bone meal.
Future implications? Assuming that the 161 past and current cases (156 died, 5 still alive: represent say, 80% of the total casualties of the most susceptible genotype (homozygous for methionine), then we can expect about 200 cases. The MM genotype is about 38% of the British population, so assuming risk factors and susceptibility are consistent, then about 300 cases could be expected in the heterozygous or valine homozygous group.
Assumptions here? Well, obviously, that the MM and MV/VV groups show similar eventual rates of infection. Also, that most of the fatalities in the MM group have already happened. Given that the presentation rates peaked in 2000 and have trended steadily down since then, this seems reasonable, and 80% is intended as a conservative figure.
However, estimates from testing appendixes are suggesting about 1 case in 4000, which is substantially higher (250 cases per million, so about 12,500 possible cases). Hopefully, like prostate cancer, it will have a long enough incubation time that most people will die of something else in the meantime. So, if you want the more worrisone paper, it's
Variant Creutzfeldt-Jakob disease: prion protein genotype analysis of positive appendix tissue samples from a retrospective prevalence study. JW Ironside et al., British Medical Journal, 2006, May 20;332(7551):1186-8.
And my family spent a year in Britain in 84/85, so I'm also interested.