Prion disease risk wider than thought?

Infectious prions–the things that cause BSE–can not only jump species barriers, but can also create new, potentially harmful prions in the infected host.

That is the finding of recent research at the University of Texas Medical Branch in Galveston.

Nature reports that
>Generally, prions are limited to a specific host and a few related species. But prions sometimes cross the species barrier to infect new hosts. Notably, prions from cows have hopped to humans, causing disease in 208 people, mostly in the UK. Now, scientists wonder if the prion-induced chronic wasting disease (CWD), which afflicts elk and deer in the US, could jump to humans. Since prion diseases have long dormant periods, the fact that there are no human cases of CWD doesn’t necessarily indicate that people won’t develop symptoms in the future.

The study showed that new prions caused disease at different rates, in different parts of the brain, and showed different resistance to protein-digesting enzymes as compared with the original strains. In other words, it rather looks as if prions have the ability to mutate every time they take up residence in a new species. That would seem to make them potentially both very infectious and very difficult to treat.

In a related story (paid content), Nature also reports that prions appear able to swan through standard sewage treatment methods. In other words, once prions get into the water system nothing presently used on an everyday basis can stop them. Commentator Robert Eibl notes, rather chillingly, that

>This doesn’t surprise me at all, since I remember a talk by one of the older researchers in the field from more than 10 years ago, that he had put one prion containing tissue (as far as I remember, a whole mouse or hamster or similar) into the soil of his garden – and, about a year later, took some earth from this area, autoclaved it at normal temperatures (which should leave remaining prions infectious) – and could transfer the disease from garden soil by infecting animal brains. This result appeared even scary to him, but in some way he expected it, too. Considering the extremely high resistance to temperature and other things, it appears to be reasonable to beleive that prions will remain infectious over decades even with millions of living bacteria surrounding them in gardens and other soil. Therefore, anywhere where prion diseases appear, special care should be taken: laboratories with animal models and infectious prions but also pathology and neuropathology rooms with Creutzfeld-Jacobs’ disease, and of course all the fields where ever Mad-cow disease occurred. [my emphasis]

When you read something like that, it strikes you for a second that it’s something of a miracle that humanity has even made it this far.