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Alzheimer's disease: the viral link
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I've written previously how microbes have been associated with obesity. Strange as it may seem, a number of other microbes have been associated with all kinds of chronic conditions, including cancer and heart disease, and may also be risk factors for brain disorders such as Alzheimer's Disease--in this case, especially viruses in the herpes family. This family of viruses includes herpes simplex virus-1 (HSV-1), human herpes virus 6 (HHV-6) type B, and cytomegalovirus (CMV), which have all been found in the brains of patients with dementia.
Approximately 85% of us are infected with HSV-1, typically in childhood: it's where those annoying
cold sores on your lip come from. However, obviously 85% of the population doesn't get AD, so just because you get cold sores doesn't mean you're going to end up with a diagnosis of probable dementia. Many other risk factors contribute to your likelihood of getting AD, such as having one or two copies of the ApoE-epsilon 4 allele. AD patients with the ApoE4 allele also tend to have higher levels of HSV-1 in their brains.
Additionally, simply being positive for HSV-1 or another of the viruses that are risk factors is not necessarily a guarantee of getting AD or another form of dementia. These viruses tend to lie dormant in the nervous system, occasionally "flaring up" and causing inflammatory responses in the brain that lead to more and more AD-like pathology. One interesting question is whether chronic, low-level infections occurring since youth contribute more to the incidence of AD, or whether the growing public health concerns surrounding increasing STD prevalence in the elderly contribute to development of dementias.
Additionally, viruses may not be the only infectious agents of concern. Infection with Chlamydia pneumoniae, a bacterium, has also been linked in some studies to an increased rate of Alzheimer's disease. It's not yet known how much of a factor these infections really are in the development of AD and other diseases, or even if they're causative or merely "bystanders," but this is an active field of research that's only gaining more attention. Stay tuned....
Tags: Alzheimer's disease, chlamydia, herpes, viruses
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January 6, 2008 7:08 PM
Michael
Interesting correlations re: AD and childhood and viruses. Certainly worth further exploration. But certainly, we do not want to jump the gun here in a fit of germaphobia, do we? As alas, the noted viruses are only correlations in some cases, and a lot of the virus types you mentioned are very common throughout populations, and even throughout populations that do not have AD.
I think it was, ummmmm, Peter Duesberg, who I first remember warning us all, by saying that "Correlations do not equate to being the cause of a disease".
Example #1: Skidmarks,
Though skidmarks are found at 100 percent of traffic accidents, they are obviously not the cause of traffic accidents.
Example # 2: HIV
HIV, as the AIDS rethinkers and dissidents have aptly shown us, is not the cause of the 30 common and uncommon diseases lumped together and called AIDS for the last 20 years.
January 6, 2008 8:21 PM
Tara C. Smith
Michael,
First, Duesberg was hardly the first to note that correlation doesn't equal causation--it's a critical concept in epidemiology. And in this case, I noted most of these are associations--we're not 100% sure right now what's causal (do the viruses help contribute to dementia, or does dementia allow the viruses to activate in neurons?) However, several lines of evidence suggest that they play a role in its development. In addition to the epidemiology, animal models have shown that animals infected with these or similar viruses develop pathology related to dementia at a higher rate than uninfected littermates. We know the temporality of this because the researchers infected them when they were young animals. There's also biologic plausibility, as the viruses are neurotropic.
These converging lines of evidence don't prove causality, but together they provide an excellent reason to continue looking into this interesting area of research.
January 6, 2008 9:34 PM
Michael
I wholeheartedly agree! Hope you are enjoying LA. Shame it is one of the few rainy weekends we get out here. If you get some time, come on down to San Diego, it's only a 2 hour train, and I'll be glad to buy you dinner and show you around. Orrrr, you could even visit Christine Maggiore while your up in LA! That might cheer you up! Sound like fun? Well, if not, it was only a passing idea!
January 7, 2008 10:31 AM
Greg
Hah! These microbe hunters like Dr. Smith are such transparently bad scientists that it defies human description. It reminds me of that old axiom -- if you go through life as a hammer, everything begins to look like a nail.
Viruses aren't "associated" with obesity (junk food, and lack of exercise are), and, certainly, viruses don't cause Alzheimer's, unless they can magically, select for really old people.
Every person lives in a sea of bacteria and viruses. Blaming them for every ailment under the sun is simply a pitiful attempt by the virus hunters to strive for relevancy and funding opportunities.
January 7, 2008 12:00 PM
cvj
So Greg, are you saying you've done the research on viruses and alzheimers and already know the answer? You seem rather sure of yourself that there's no connection, so I assume you have a body of peer-reviewed literature you can point to that answers the questions the researchers are asking.
-cvj
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