Mysterious Prion Diseases, from Mad Cow to Fatal Insomnia
Another addition to your nursing lexicon
Prions are strange little things. Elusive not just in appearance but also in function, they seem to be responsible for a collection of neurological diseases, transmissible spongiform encephalopathies (TSEs), all of them ugly and all of them fatal. None of the diseases afflict a large number of people. But when you examine them, you can’t help but develop a lurking suspicion that perhaps prions are responsible for much more havoc than we appreciate. My own informal survey of other nurses indicates prion diseases aren’t even on their radar, and yet, current infection control manuals, CDC, FDA, and USDA updates refer to prions.
To confuse the issue, there is a curious lack of consensus among those who study them. Do prions (pree-ons in America, pry-ons, elsewhere) really exist, and if they do, can scientists say they cause a specific disease? Does the small risk of contracting one of these illnesses justify this or that protocol? All are interesting questions, but there are no easy answers.
A Misshapen Protein that Wreaks Havoc
Most scientists believe that prions, best described as rogue proteins, do cause some maladies. The tricky part is how. The word “prion,” a loose acronym for proteinaceous infectious particle, was coined by Nobel Laureate Stanley Prusiner, MD, during his early years of work on these microscopic particles. The term refers to a harmless protein found in body cells and also to the almost identical yet misshapen proteins that can cause disease, those that are bent or miss-folded.
The unusual properties of prions are where the difficulty arises. Apparently, they reproduce without nucleic acid, a circumstance unknown in any other organism. Instead, prions seem to mysteriously convert a normal host protein to an abnormal form. No one has identified the exact mechanism at work, and therein lies part of the problem.
Another difficulty is the prion’s supposed ability to transmit disease through infectious transmission, heredity and sporadic episodes of spontaneous mutation. That threefold route of transmission is not true of viruses, bacteria, or parasites, and it’s another reason some researchers harbor doubts that prions are agents of disease. These dissenting scientists have concluded variously that prions are really “slow viruses” or that RNA or DNA material (nucleic) is really present. They argue the usual hereditary material merely is not discernible with current methods of detection.
One huge additional area of concern is that ordinary sterilization methods like standard autoclaving, radiation, or ethylene oxide do not eradicate these snarky little items. This characteristic has enormous implications for reusable medical equipment employed in invasive procedures: dental probes, endoscopy equipment, surgical instruments, among others. Research continues. How hot should the autoclave be? For how long should it run? Should anything used invasively on a suspected TSE victim be reused? Who are the victims?
Meanwhile, how does this confused state of affairs affect us as nurses? Well, would you rather err on the side of caution or would you rather assume what you don’t know won’t hurt you? The latter attitude might work when you ignore the calorie count in your favorite frappucino. It might not be so wise when you eat steak, or when you take dietary supplements with animal components. Why? Because bovine spongiform encephalopathy (mad cow) is strongly implicated in the rise in variant Creutzfeld-Jakob disease (CJD) in Europe and Great Britain.
Fatal familial insomnia afflicts about 40 families worldwide. It is a hereditary curse that appears in middle age, causing the victim to suffer an inability to sleep, eventual ataxia, dementia and invariably death in about 18 months. Many cases trace to an Italian nobleman who succumbed to the disease over 200 years ago. Fortunately, current family members have thrown off the secrecy surrounding their hereditary disorder, and indeed, they have set up a foundation to fund research into this disease. Check out their website at www.afiff.org for a fascinating description from the doctor treating some of these patients.
Gerstmann-Sträussler-Scheinker Disease is found in only a few families, and is almost always hereditary. Not to be confused with Gerstmann’s Syndrome, which is usually a developmental or post-stroke phenomenon, GSS is a slowly progressive disease that can last from two to 10 years. It invariably, like all TSEs, causes death but not before its victims suffer major neurological impairments.
Thankfully, kuru, once endemic in New Guinea, is on the wane, close to being eradicated. It is primarily of historic interest, having occurred only in tribal members who practiced cannibalism. But kuru can serve as a cautionary lesson. Because of its characteristically long incubation period, it was very hard to track epidemiologically. All TSEs have a long incubation period, and apparently none causes an inflammatory or immunological event to herald its onset.
That brings us back to Creutzfeldt-Jakob, the most common of the spongiform encephalopathies, but still, a rare disease, once thought to be hereditary or occasionally spontaneous (sporadic). When mad cow disease first broke out in Great Britain, no one saw it as the same sort of affliction—scrapie—that has plagued sheep for centuries. No one knew it could cross species, that it was zoonotic. Only after hundreds of thousands of people ate contaminated cattle did scientists make the link. And by the time the connection to Creutzfeldt-Jakob became clear, sick beef had spread through much of Europe.
Now, because of the long incubation period, no one really knows whether a huge epidemic was avoided because most Brits are immune or because the “new” variant of CJD is really not a form of mad cow.
Another alternative is that there’s a hidden time bomb in the population few want to see. No diagnostic tests exist; a confirmed case comes only at autopsy. Fortunately, the United States has so far escaped this uncertainty. Agriculture Secretary Mike Johanns tells us we have “a very, very low level of BSE in the United States.” There has not been a single case of variant CJD—except in a woman who spent time in Britain. Still, even here, there are the occasional victims of the apparently sporadic Creutzfeldt-Jakob that occur in all populations. And from them have come the iatrogenic cases that led to the restriction on human growth hormone. Remember when that was big? Corneal and dura matter transplants have also been implicated, and new restrictions have been imposed. Does the Red Cross ask about travel to weed out parasitic and viral diseases? Yes, but they also ask about travel to Europe and England to eliminate possible TSE transmission. In fact, the American Red Cross rejects donors that have resided a cumulative six months in either location, between the years of 1980 and 1996.
There is as yet no conclusive evidence that TSEs are blood-borne, but there is suspicion that they might be. When an agent is found in lymph, body fluids, and plasma products, who wants to take a chance? What is disconcerting is that the six month time-frame was imposed to lessen the impact on the blood supply rather than as a reflection of the risk of transmission. In fact, the CDC and the FDA continue to revise guidelines based on the available evidence. One recent piece of good news about blood is the announcement of a new filter to remove mutant proteins prior to transfusion, (Dec. 23/30, 2006 Lancet.)
Pay attention, not to what just appears in FDA and CDC directives. These take awhile to trickle down to the local level. They are also the results of group consensus, the lowest common denominator, and neither agency is noted for aggressive surveillance. Read across disciplines and make up your own mind. Watch what goes into your mouth and where it originates. For more information, you might look into the DVD put out by the Creutzfeldt-Jakob Foundation, “Confronting CJD and Other Prion Diseases,” an hour long presentation of lectures by some of the world’s leading prion disease experts. It would make a wonderful addition to your hospital or nursing school library.
Elizabeth Hanink, RN, BSN, PHN is a freelance writer in Los Angeles, CA. She has 30 years of nursing experience.
This article is from workingnurse.com.