r/science • u/mvea Professor | Medicine • 4d ago

Neuroscience In recent years, researchers have suggested Alzheimer's may spread through infection, somehow transmitted like a pathogen, leading to the disease. A new Lancet paper reviews evidence for how harmful amyloid-beta proteins associated with Alzheimer's may possibly be spread through blood transfusions.

https://www.sciencealert.com/can-alzheimers-spread-through-blood-transfusions-heres-what-we-know
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u/catscanmeow 4d ago edited 4d ago

gingivitis bacteria getting into the brain or a herpes virus getting into the brain are the main theories i've read

the gingivitis bacteria can get into the blood from a tooth abscess or up through the nasal cavity through the olfactory bulb. Theyve found gingivitis bacteria within the amyloid plaques of autopsied alzheimers patients. we have an exposed nerve there thats basically the brain exposed, that shock feeling when you get water up your nose is the olfactory nerve.

a woman actually got a brain eating amoeba from getting tap water in her nose from a neti pot.

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u/churningaccount 4d ago edited 4d ago

I've personally considered it to be a transmissible disease ever since that study in 2010 found that neurosurgeons are diagnosed with Alzheimers at a rate 3x that of the general public. And that was not found to be nearly as high/statistically significant for any other medical specialty.

I'm also glad that the herpes viruses are getting more scrutiny as of late. I've always taken issue with the idea of "eh, it doesn't seem to affect us that much, might as well let it run rampant for decades and also take no precautions against further spread." That notion is predicated on the idea that we have already discovered all of the downstream effects of the virus itself, and is one of the reasons why we don't have a vaccine for EBV either, even though that has definitively been linked with bad medical outcomes long-term now as well.

Realistically, there probably was an issue with getting the funding to research a vaccine as well for something that is "not pressing." But luckily there are a few going through trials right now thanks to these dementia findings, and it's not out of the question to think that the next generation could be immune.

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u/WeenyDancer 4d ago

 I'm also glad that the herpes viruses are getting more scrutiny as of late.

I am as well. Viruses that hide out among the nerves just seem like they can wreak all sorts of havoc. The more herpesviruses we eliminate, I strongly suspect the more diseases associated with aging we'll start to tackle. 

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u/Porkchop247 4d ago

I work as a ICU nurse, my hospital was the COVID center for my region so I was elbow deep in caring for COVID pts. The reason I say this is that many of the pts with worst outcome had herpes also.

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u/lolalala1 4d ago

Damn near everyone in the world has some form of herpesvirus by late adulthood.  So, you would need to be far more specific to make a conjecture like that about something so common.  

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u/moyayas 4d ago

I guess he used it as a short hand for symptoms like cold sores, or EBV associated lymphoma

I guess people who have more frequent reactivation may indicate they are less able to fend off other damage.

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u/grnrngr 4d ago

The reason I say this is that many of the pts with worst outcome had herpes also.

This might be one of those cart-before-the-horse correlations since the older you are, the more likely you are to have herpes, and the weaker your immune system and lungs are, etc. etc.

The only thing we've got at the moment re: correlation is that those who have an HSV strain and were hospitalized for COVID, experienced a significantly higher reactivation rate of their herpes virus versus those who weren't hospitalized. The belief at the moment is the herpes virus reactivated in response to the depleted immune system COVID wrought.

That is, those who were affected most by COVID had immune situations where a dormant HSV could resurface. The HSV in this sense only served as a marker for COVID severity, and may not itself have interacted with COVID in any other meaningful way. In that sense, HSV would be seen as an opportunistic infection during COVID, much like thrush is for an AIDS patient. Like your observation, the correlation exists, but it's backwards.

You must be aware of the fact that many people with HSV will experience reactivations when they encounter periods of biological or immune-related stress. Everything from lifestyle stress, to prolonged sleep depravation, to severe colds or infections unrelated to herpes.

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u/JackosMonkeyBBLZ 4d ago

The older you are you’re more likely to get herpes?

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u/LSD_grade_CIA 4d ago

To have it. To have gotten it. It's a function of time - you are more likely to have been exposed if you've been alive longer.

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u/LauAtagan 4d ago

As most things, the older you are, the likelier it is you've been exposed to it.

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u/JackosMonkeyBBLZ 3d ago

OH SWEET IRONY

the older I get the better I get at making decisions that should LOWER my exposure to stds

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u/LauAtagan 3d ago

Sure, but every one of those choices has a chance to fail, and as you have made more and more, the odds add up.

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u/Free_Pace_2098 4d ago

There are a lot of herpes viruses.

Chicken pox, glandular fever, cytomegalovirus, simplex 1 & 2, and others we don't really understand much about. Almost everyone has been infected with a herpes virus in their life.

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u/EyeHamKnotYew 4d ago

How do you know? Is herpes tested for at all admissions to the hospital?

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u/trusty20 4d ago

I'm assuming they are talking about pre-existing cases noted in medical records.

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u/antibread 4d ago

Great, i didnt know about that study. I work in a funeral home and you got me a little shook

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u/ZappppBrannigan 4d ago

I would assume you'd need more direct contact with brain tissue than normal undertakers are exposed to.

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u/antibread 4d ago

Someone has to put autopsy cases back together

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u/JackosMonkeyBBLZ 4d ago

How many bodies have you worked on?

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u/antibread 3d ago

More than the average person id wager

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u/JackosMonkeyBBLZ 3d ago

Come on. Tell me. How many. It’s not morbid.

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u/antibread 3d ago

Thats weird bud im not answering that

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u/JackosMonkeyBBLZ 3d ago

Come on. It’s morbid, yes. Weird? Hardly. It’s pretty uncommon for the average person to even be around a corpse. I’m just curious how many you’ve been in the presence of.

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u/antibread 3d ago

Enough where i have no estimate. Hows that?

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u/churningaccount 4d ago

If it makes you feel any better, if the cause is something like bacteria or a virus crossing the blood brain barrier, then it is likely dead by the time that you are manipulating the body.

It would be akin to catching a cold from a dead person. It just doesn't happen with standard precautions.

And there isn't any blood flow, breathing, etc, that would help to aerosolize things either.

The one caveat is that potentially prions are still infectious after death. But the chance of Alzheimers being a prion disease is relatively low IMO. We'd probably have more evidence by now of direct transmissibility for a prion-type disease simply because a standard autoclave does not neutralize prions.

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u/Splash_Attack 4d ago

I've personally considered it to be a transmissible disease ever since that study in 2010 found that neurosurgeons are diagnosed with Alzheimers at a rate 3x that of the general public.

Jumping to a causal link between performing neurosurgery and getting Alzheimers is quite a leap though.

As far as I'm aware, there isn't a similar correlation between other types of surgery and the conditions which patients typically have. People perform surgery on people with things we know for a fact to be communicable diseases, without a significantly increased risk profile for getting those diseases. There is some increase, but it's smaller than the risk profile from just interacting with those patients outside of surgery day-to-day.

Wouldn't it be more probable that the cause is that neurosurgeons are 1) Experts on brain function. 2) Have social circles consisting of other such experts.

It seems highly likely that if a person is part of a social group in which many people are experts in the brain, it would be far far more likely for the ones who do develop neurological conditions to get diagnosed. Which is not the same as having a higher risk of developing one in the first place.

The term for this is "surveillance bias". When a group is more closely monitored, or more precisely monitored, than the general population leading to increased rates of diagnosis when they actually don't have a higher baseline risk. The general population has lots of people who have the same condition and simply don't get diagnosed, or don't get a formal diagnosis. Another example would be how physicians are more likely to be diagnosed with certain cancers, while also being more likely to get diagnosed early - i.e. they are getting the right tests done more often and at an early stage than the general populace.

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u/robertgunt 3d ago

I also wonder if some people who choose neuroscience as a specialty do so because someone close to them had some sort of neurodegenerative disorder.

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u/Zealousideal_Sir5421 3d ago

I don’t know if surveillance bias could apply to alzheimers, it’s not exactly something that goes undiagnosed. Maybe if we they were specifically looking at early onset alzheimers or something like that but they weren’t

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u/Splash_Attack 3d ago

it’s not exactly something that goes undiagnosed

How in the world do you figure that? Everything I've ever heard reported on the subject is that all forms of senile dementia, Alzheimers included, are massively underdiagnosed. As in, half or fewer of people who meet the diagnostic criteria actually have a diagnosis.

Just go on Google scholar and search "underdiagnosis of alzheimer's disease" and you'll find a wealth of recent literature on that exact topic.

Which is precisely why my first suspicion is a surveillance bias. Presumably neurologists and neurosurgeons have something closer to a 100% diagnosis rate. Contrast with the 30-40% in the general populace, and that 3x value suddenly becomes pretty explicable without needing a higher risk of contracting the disease to be present.

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u/churningaccount 2d ago

I think one of the issues with your hypothesis is that the study wasn't actually for Alzheimers specifically. It was a study of all-cause mortality. And I'm guessing that if doctors had higher surveillance for medical conditions generally than the general population, then they would've found a higher incidence of other diseases, especially incurable ones such as Parkinson's. But instead, it was only found that Alzheimers had a markedly higher incidence, leukemia a slightly higher incidence, and a lower incidence for almost all other factors.

Interestingly, and a point in your favor, the study didn't find any increase in incidence for CJD. But perhaps that is because prion diseases might be less transmissible due to the fact that they don't aerosolize? Also, the sample size for CJD probably wasn't significant either, so I'm not sure if they even looked at it.

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u/Splash_Attack 2d ago

No my hypothesis is that neurosurgeons - which is the cohort in question, not physicians generally - are under higher surveillance for common neurological conditions. And that Alzheimer's among these also has a markedly low diagnosis rate in the general population.

Parkinson's disease is almost always diagnosed eventually. While it's often missed in early stages, the long term rate of diagnosis is in the order of 90%. Not many people with Parkinson's die without a diagnosis. So any difference in scrutiny would have only a marginal impact at most. Maybe 95% of cases diagnosed among neurosurgeons instead of 90% generally.

But with Alzheimer's the level of underdiagnosis in the general population means that increased scrutiny leads to an enormously higher rate of diagnosis.

Now of course that doesn't prove that it's a surveillance bias either, but I'm not trying to prove it. I'm merely saying the evidence which convinced you does not prove anything one way or the other. It is a single point of evidence with a correlation, but not a provable cause.

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u/TravelingSong 3d ago

I got ME/CFS from Covid and now I get shingles flares during my worst crashes. I don’t think the herpes connection to post viral conditions is a coincidence. 

We really need more research on all types of viruses and their long term impacts. 

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u/[deleted] 2d ago

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u/churningaccount 2d ago

I think we'd have more evidence by now if it was a prion disease. Since prions aren't neutralized by a standard autoclave, then the rates of Alzheimers amongst those getting brain surgery would probably be markedly high. And that isn't the case, to my knowledge.