Some fascinating news this week on the topic of Alzheimer’s! The cause has long been thought to be amyloid plaques which build up in the brains of sufferers, but that theory has been dealt a blow in two ways: first, healthy people can have amyloid plaques in their brains as well, and secondly, things which prevent the buildup of the plaques don’t significantly slow the progression of disease.
That’s really a pretty huge blow. When it comes to microbial illness, the gold standard to consider is usually Koch’s postulates. They don’t always hold true in some rare cases, but they’re a really good rule of thumb when it comes to understanding the cause of an illness. To prove beyond reasonable doubt that a microbial agent is the cause of an illness, Koch suggested that:
- The agent must be present in every case of the disease.
- The agent must be isolated from the host with the disease and grown in pure culture.
- The specific disease must be reproduced when injected into a healthy, susceptible host.
- The agent must be recoverable again from that new host.
This doesn’t apply to all kinds of illness, and prion diseases like scrapie and bovine spongiform encephalopathy don’t follow these rules for example, but you can see how important the postulates are in picking apart correlation and causation. For instance, we all carry certain non-harmful bacteria in our bodies, and they will most likely be present in every case of E.coli food poisoning. However, they would then fail at the point of reproducing the same illness in a different host. In the same way, we can see that amyloid plaques aren’t the be-all and end-all.
But there might just be something that is. Studies are finding that amyloid plaques are actually a response to microbial invasion of the brain. The culprit — so the new theory goes? The microbe responsible for gum disease: Porphyromonas gingivalis. In mice, infection with P. gingivalis led to Alzheimer’s symptoms, while treating the infection then improved them. The same has held true in some human volunteers. So it’s looking like a good bet for a causative agent — though possibly not the only one.
I don’t know about you, but I think I’m going to get on top of that little gum disease problem I’ve got going on.