Alzheimer's may be transmissible from one person to another
The mad cow disease (Creutzfeldt-Jakob Disease as it's known in humans) terrified people worldwide and put many off of eating beef, worried they would catch the disease that turned the brains of both cattle and humans "into soup." While the threat turned out to be more hype than reality — it was harder to catch the illness than just eating a hamburger and there are only about 300 cases each year in the U.S. — it did introduce the world to a new category of disease: infectious prion diseases.
And now, after a recent surprise discovery in a mad cow/CJD lab, infectious disease researchers are wondering if illnesses like Alzheimer's and Parkinson's can spread through contaminated tissues just like the illness that made cows a cartoon horror show. If it is possible to transmit them from person to person, it could have huge implications for our public health system.
How exactly people get Alzheimer's disease is unknown. We do know that the neurodegenerative disorder mainly affects old people but develops years, even decades, before people show symptoms and that some of the illness is linked to lifestyle factors. In brain biopsies, Alzheimer's is characterized by particular "plaques" and "tangles" caused by certain amyloids — misfolded proteins that cause over 30 human diseases including Alzheimer's and Parkinson's.
So here's where the link to CJD comes in: Prions, the malfunction that causes CJD, are a type of amyloid, similar to the ones that cause other neurodegenerative diseases. And we've long known that prions can be transmitted from one creature to another, by eating or otherwise taking in tissue from a sick animal or person, a la mad cow. So if those particular amyloids can be shared does that mean all amyloids, including those that cause Alzheimer's and Parkinson's diseases, are also contagious?
The answer appears to be yes, says John Collinge, a neurologist who specializes in prion diseases. Late last year he found Alzheimer's plaques in the brains of patients who had accidentally gotten CJD from human growth hormone injections contaminated with, apparently, both diseases.
But before you panic about visiting Grandma, this doesn't mean you can get Alzheimer's from being sneezed on by a stranger or even from caring daily for a patient. The spread (if it does spread the way they think it might) would only happen the same way CJD does: by somehow getting infected tissue inside you. Since thankfully we don't eat people, the most common method of contamination would likely be through medical treatments and surgeries.
The problem is that amyloids "stick like glue" to metal surgical instruments, and normal sterilization does not remove them, so it's possible that amyloid seeds could be transferred from a sick patient to a healthy one during surgery, according to a report published in Nature. Not only might this set up healthy patients to contract the neurodegenerative diseases later, but amyloids also increase the risk of stroke.
If Collinge and others are correct, this could spark a public health crisis. The primary and most immediate need is a way to clean surgical instruments that would wipe them clean of all amyloids, along with traditional germs like bacteria. And while some methods do exist there aren't any at present that are cheap and could be quickly or easily implemented in all hospitals. The second issue is the need to scan all donated human tissues — including organs, blood and any products made from human tissues like human growth hormone — for rogue amyloid seeds.
While researchers continue to hash out the details on whether or not Alzheimer's is transmissible — and it is by no means a settled conclusion — the best defense appears living as healthy a lifestyle as possible and taking steps that we know can reduce your risk of Alzheimer's, like eating a Mediterranean diet and getting regular exercise.