Hot Topic: Environmental toxicants and their role in Parkinson's disease

Ray, I don't think you need much of an introduction for our audience. On a personal note, as a fellow, I came to know you as a telemedicine enthusiast when I first began my research journey in that arena, and over the last decade your focus has really shifted towards Parkinson's disease prevention.

Today, we are going to discuss many of the topics discussed in your paper entitled, "Environmental [00:01:00] Toxicants and Parkinson's Disease: Recent Evidence, Risks, and Prevention Opportunities," published in the November 2025 issue of Lancet Neurology, the senior author being the inimitable Carlie Tanner. Welcome, Ray.

Thank you so much for taking the time today.

Dr. Ray Dorsey: Thank you for having me, Mitra. I'm delighted to be with you.

Dr. Mitra Afshari: So, over the years, there's been mounting evidence for several extrinsic or environmental factors linked to the development of Parkinson's disease. And in this paper, Ray, you examine three of the most strongly implicated environmental toxicants: pesticides, dry cleaning and degreasing agents, and air pollution.

My first question to you would be, could you provide one or two examples of each of these toxicants that fall into these three categories that have really shown that connection to Parkinson's disease?

Dr. Ray Dorsey: Yeah. So let me just take a step back. First of all, why do we think that these [00:02:00] diseases are preventable, and what are the causes, principal causes of Parkinson's disease? One central tenet of Western medicine is that diseases have causes. You don't get Parkinson's disease, you don't get cancer because of the sins of your aunt.

You get cancer or Parkinson's disease because something caused you to have the disease. You get pneumonia because you got exposed to a virus or a bacteria, and that gave you infectious disease. So what causes Parkinson's disease? So we had some great data from genetics from PD GENEration, a study led by the Parkinson's Foundation, similar study done in Europe called the Rostock Study.

13% to 15% of people with Parkinson's disease carry a genetic cause or genetic risk factor for it. Said another way, 85% of people with Parkinson's disease carry no known genetic cause or genetic risk factor, and this is true for just about every part of the world that's been examined. We also know that people like to implicate aging.

Longevity and long life is clearly a prerequisite, generally speaking, for Parkinson's disease. If everyone died at age 30 or age 40, there'd be very little Parkinson's [00:03:00] disease in the world. And the incidence of Parkinson's triples every decade beginning in your 30s. It turns out another disease called lung cancer has the exact same incidence curve.

And I think for both Parkinson's and for lung cancer, you get exposed to these chemicals when you're young, whether it's tobacco smoke or, say, pesticides, and then years, decades later, you develop the disease, whether that's lung cancer from smoking or Parkinson's disease, say for example, for pesticides.

And Dr. Tanner did a twin study in 1999, published in JAMA, showing that the concordance rate among identical twins and fraternal twins was virtually identical. Her conclusion in 1999 was that genetics plays a very little role in Parkinson's disease, but for people who have early-onset Parkinson's disease, it may play a modest role.

And she was right in 1999. She was right in the 1980s when she said that environmental chemicals are likely underlying a lot of Parkinson's disease. And all her research for the past 40 years [00:04:00] has basically told us that the principal causes of Parkinson's disease do not lie in our DNA.

They're not inside of us. It's not like Huntington's disease, which I spent the first decade of my academic career working on. Probably never said the word environment. The principal causes are not in our DNA, not in our genes. They are outside in our environment.

So what in our environment is contributing to the rise of Parkinson's disease? And as you rightly point out, we highlighted three sets of chemicals. The list is long, and it's not exclusive.

One are pesticides. Many of these pesticides are designed to damage the nervous system of insects. And it should be not terribly surprising that chemicals that are designed to damage the nervous system of insects might have untoward consequences on the nervous system of humans. The pesticide that's most clearly associated with Parkinson's disease is a pesticide called paraquat.

I think just about everyone knows about paraquat, a weed killer sprayed on fields of corn, cotton, and soybeans throughout the United States. Over 70 countries, including China, have banned it. The United States has yet to act, [00:05:00] even though research done by Dr. Deborah Cory-Slechta, a neurotoxicologist at the University of Rochester, showed that rodents exposed to paraquat move around less, and they have the pathological features of the disease.

She did that in the late 1990s. Dr. Tanner, I think in 2011 or 2012, showed that farmers who work with paraquat have 150% increased risk of disease. These studies have been replicated by scientists around the world. There's not much doubt that it causes it.

The second class are organochlorine pesticides.

These pesticides, like DDT, the poster child, again, relatively recently introduced, chiefly during World War II where they were sprayed to kill mosquitoes and save millions of people from getting malaria. After World War II, the problem was that they were indiscriminate and widely used, leading to declines in bird populations and adverse health consequences for humans.

Rachel Carson, another woman, wrote about this in 1962. She said in 1962 that because of the widespread use of DDT, new kinds of [00:06:00] illnesses would appear among farmers that would puzzle the doctors in the cities. Sounds like Parkinson's disease.

And these chemicals are fat-loving. They're lipophilic. They damage dopamine-producing neurons in the lab, and you can find them in the fat tissue of humans. You can find them in the breast milk of women. You can find them in the brains of people with Parkinson's disease. Dr. Tanner and Dr. Webster Ross, Dr. Juan Sanchez-Ramos, and others have done this work.

So I think there's little doubt that pesticides, especially paraquat and organochlorine pesticides, are playing a role. I think we all heard a little bit about this during our training, but I think there's a lot there.

Second is dry cleaning chemicals. So what in the world does dry cleaning have to do with Parkinson's disease? Do you know, Mitra, why we dry clean clothes?

Dr. Mitra Afshari: No, I actually don't.

Dr. Ray Dorsey: Yeah. So this is fantastic. So we dry clean clothes so our clothes don't shrink. In the late 1800s, early 1900s, the dry cleaning agent of choice was kerosene. Unfortunately, kerosene has the unfortunate property [00:07:00] of being flammable. So in the 1930s, a chemical called trichloroethylene, I know your listeners can't see my beautiful chemistry model, but trichloroethylene is made up of six atoms.

It's got two carbon atoms, one hydrogen atom, and then three chlorine atoms, hence its name trichloroethylene. It's got a cousin called perchloroethylene or tetrachloroethylene. Instead of three chlorine atoms, it has four. And in 1930s, trichloroethylene was used in dry cleaning because it's not flammable.

Fantastic. Then it was largely used until 1950s until perchloroethylene or tetrachloroethylene took over in the dry cleaning industry. Today, if you're dry cleaning your clothes in the United States, most dry cleaners are using perchloroethylene, called perc in the industry. Listeners are going to switch their dry cleaning habits after this call because Dr. Tanner again and her colleague Dr. Sam Goldman showed in Annals of Neurology that exposure to these chemicals is associated with a 500% increased risk of developing the disease. In the lab at University of Kentucky, Don [00:08:00] Gash, Dr. Briana de Miranda, I think Dr. Tim Greenamyre, and others have shown that TCE replicates the effects of Parkinson's disease. Animals develop a tremor, and it damages dopaminergic neurons. I think it's even been shown to create Lewy bodies. TCE increases LRRK2 kinase activity, mimicking the effects of LRRK2 mutations.

So we have data from the lab, from epidemiological studies, including Camp Lejeune. Marines who served at this Marine base in North Carolina contaminated with this chemical had a 70% increased risk of developing Parkinson's disease 34 years after their exposure. Dr. Tanner, Dr. Sam Goldman as well. So, evidence from the lab, from epidemiological studies, and a mechanistic thing mimicking the most common genetic cause of Parkinson's disease.

I'm not sure what more you would want to have.

And then the third and last one is air pollution. When Dr. Parkinson is describing a condition in 1817 that he said had not been classed by the medical literature. He went [00:09:00] to great lengths to show that tremor had long since been described and said scientists Dr. Smith and Dr. Jones described tremor, but this tremor, this stooped posture, this tendency to walk forward and to fall forward, this to him was a new disease. What was going on in 1800 London? No pesticides, no synthetic pesticides. There's naturally occurring pesticides, but not synthetic pesticides.

No dry cleaning chemicals in 1817 London. What's going on? What's going on is the Industrial Revolution has begun. London is its capital. The air quality over London is terrible. Many listeners, especially in the States, have experienced the consequences of the Canadian wildfires. In Chicago, where you were, I think July 6th or so had the worst air quality probably ever recorded in the history of Chicago.

Dr. Mitra Afshari: Right.

Dr. Ray Dorsey: That level of air quality still did not match 1800 London. And on numerous studies Dr. Debbie Cory-Slechta, others, have shown with somewhat consistent results that air pollution is linked to Parkinson's disease. Air pollution is clearly linked [00:10:00] to a wide range of other neurodegenerative diseases, and studies suggest that the higher the level of the air pollution, the greater the risk.

And then 1800 London is really high. And so I think that's the third major risk factor. So certain pesticides, especially paraquat and organochlorines, dry cleaning chemicals, trichloroethylene and perchloroethylene, and then air pollution I think are the three biggest risk factors.

And I think that the central tenet is that Parkinson's disease is predominantly determined not by our genes but by our environment. Genes might determine who among us who are exposed to these chemicals are more likely to develop the disease, but the principal cause that's acting upon us are these environmental chemicals, and therefore Parkinson's is preventable.

Dr. Mitra Afshari: Thank you so much for that review, Ray. That was fantastic. You mentioned the Camp Lejeune study, and can you describe various findings in that study and how that study specifically really provided some critical pieces of information in our overall understanding of how PD develops and the various avenues by which [00:11:00] we can get exposed to these toxicants?

Dr. Ray Dorsey: Yeah. Kudos to Dr. Sam Goldman, Dr. Caroline Tanner, and their colleagues I think 2023 JAMA Neurology. Camp Lejeune is a big Marine base. Think of it like a huge university. Think of like Ohio State University or University of Illinois in Champaign. And it's a principal site by where Marines are trained in the United States, Marines or members of the military.

And from 1953 to 1987, the drinking water at the Marine base was contaminated with these dry cleaning chemicals. Marine officers need to have their uniforms dry cleaned. There was a dry cleaner right on the base or right off the base where the Marines went, and those dry cleaning chemicals were inappropriately disposed of, and they contaminated the drinking water there, along with other sources.

It was considered the most toxic exposure to trichloroethylene documented in human history, according to the National Academy of Medicine, something to that extent. Trichloroethylene is known to cause cancer. It's linked to miscarriages and a wide range of other diseases. So many children died at Camp Lejeune that they have [00:12:00] a cemetery right off the base called Baby Heaven, where these babies are buried.

Some were actually born without brains. Dr. Tanner and Dr. Goldman were focused on Parkinson's disease, and they looked at Marines who served there in the 1970s when the levels were at around their highest. And they looked at Marines who served there. And one, by definition, they were healthy, right?

To be a Marine, you have to be healthy. Two, they were young. The average age of this cohort was 20. Some were teenagers when they were exposed. Three, they're only there for a short period of time. In the United States, you move from base to base. The average duration of exposure was 25 months. I think the shortest might have been 6 months, might have been been less.

And then they followed them to see who developed Parkinson's disease. The average age of the cohort when they examined it was 60, so these are still young individuals. But the Marines who served at this Marine base had a 70% higher risk of developing Parkinson's disease than the Marines who served at a less contaminated base called Camp Pendleton in California.

And they [00:13:00] showed the average length of time between exposure and onset of the disease was 33 to 34 years. So we have a couple things to take away . One, the seeds of these diseases are planted early, so in this case, at average age of 20. Two, there's a long lag time. In this case, 33 years, a high range of variability range from 5 to 45 years. And three, that these chemicals are associated with an increased risk of developing the disease.

It fits in very well with what we know about the disease, that there's a long lag time over which time the pathology develops. And that early childhood exposure might, or early adulthood exposure in this case, might sow the seeds for developing Parkinson's later.

It's worth noting that this cohort's young, so more cases of Parkinson's disease will likely manifest in the future as this cohort ages.

Dr. Mitra Afshari: So when you're exposed is really important. You answered that question, but how you're exposed is also important, right? This is really fascinating literature in the TCE world, right? Do you think it's [00:14:00] ingestion or inhalation or both that are the culprit, or do you think one could be more potent than the other?

Dr. Ray Dorsey: Just one thing on the age. That cohort examined Marines, but of course, the Marine base had children there. So the former NBA basketball player, Brian Grant, was a 3-year-old boy when his father, a Marine, was stationed there, and his father dies of cancer linked to trichloroethylene.

He himself, 33 years later, developed Parkinson's disease. Our next book, which Michael Okun and I are working on, we're gonna talk about the children of Camp Lejeune. We've met people who were conceived at Camp Lejeune and then later developed Parkinson's disease.

Route of exposure. So trichloroethylene is in the water, it was in the drinking water, and the Marine Corps actually knew about this contamination for the latter years and did nothing about it. It wouldn't even notify people after the fact until Congress required them to do so. Most people tend to focus on it being ingested, and that could be a means by which you develop the disease.

Dr. Brock in 2003 says that Parkinson's disease begins from [00:15:00] neuro invasion of a pathogen that crosses the mucosal barrier. Trichloroethylene is fat-loving, could readily cross the mucosal barrier and, he doesn't quite say this, but leading to misfolding of protein and the pathology of Parkinson's disease that could spread like a falling row of dominoes up the vagus nerve in the dorsal motor nucleus of the vagus up to the pons and then to the midbrain.

As the pathology spreads, new symptoms develop: constipation, sleep disturbances, REM sleep behavior disorder, and then the motor features of the disease. And that's entirely possible. It turns out trichloroethylene is really volatile. That's why it's great as a dry cleaning agent, because you heat it up and it evaporates.

And trichloroethylene was in the water, so it wasn't just drinking. You were cooking with it, so you can breathe it when you're making spaghetti. Or your kids or you when you take a shower can be breathing it in. And Dr. Briana De Miranda, again, has shown that the potency of trichloroethylene tends to be greatest when it's inhaled.

So we don't know from Camp Lejeune, [00:16:00] for example, whether it's ingestion or inhalation. Others could argue about skin absorption as well. I think for the purposes of Parkinson's disease, I think it's ingestion or inhalation that's most concerning. I personally worry most about inhalation.

I'll give you an example why. A small Dutch study looked at different occupations and risk of Parkinson's disease, you know, accountants, teachers, mechanics, and the like, and the occupation that had the highest increased risk was female dry cleaning workers: 1,500% increased risk.

1,500%. What gives you 1,500%? And there, obviously the route of exposure would likely be principally inhalation. So I would get most worried about inhalation, not to preclude ingestion as a means, and clearly that was a route of exposure for these Marines. And I think you could look, if you could really do detailed, that if it's ingestion, I think you get early constipation, you get early sleep disturbances, you get more symmetric parkinsonism because the gut's innervated by both vagus nerves and by both sides of the sympathetic chain.

And then you [00:17:00] could also then look and see if others, for example, had loss of smell ... and that might have a cognitive function to it. But, amygdala pathology and the like. If we had brains from these individuals, it could help us determine where the disease might be beginning and which routes are more important.

Dr. Mitra Afshari: You're alluding to this, Ray. There's a lot of unanswered questions. Could you give us a synopsis of what those gaps in the research with respect to environmental toxicants are in PD? You have a whole wonderful section in your paper about this.

Dr. Ray Dorsey: One is why are there gaps? And I think we need to take some responsibility for this. We've known for 100 years that only 15% of people with Parkinson's have hereditary disease. I have the bible of neurology, you can't see it but it's called "Diseases of the Nervous System," written by Dr. William Gowers. And Dr. Gowers wrote this huge, outstanding book in 1888. And I'll read you a little bit of it. Let's see if I can get this. This is on paralysis agitans, which is what he called PD. He [00:18:00] said, "Heredity can seldom be traced in the disease, perhaps in not more than 15%."

So we've known for 100 plus years that only about 15% of people with Parkinson's have a family history of the disease. We've known from the PD GENEration study and the Rostock study that less than 15% of people carry a genetic risk factor. But if you look at the publications of Parkinson's disease, they're 6 to 1 on the genetics versus the environment of Parkinson's disease.

If we heeded the words of Dr. Caroline Tanner for the last 40 years, we would not be where we are today, where Parkinson's is one of the world's fastest growing brain diseases. There's a huge amount that we don't know. The PD GENEration study recommended genetic testing for people with Parkinson's disease.

But we never, almost never, measure chemicals in people's bodies with Parkinson's disease. Why aren't we measuring pesticides in people when we see people with Parkinson's disease? Why aren't we measuring polyaromatic hydrocarbons, a product of air pollution, in their urine when you see someone with Parkinson's disease in [00:19:00] Chicago, maybe with an exacerbation of their Parkinson's disease?

There are studies suggest that even people who already have the disease exposed to high levels of air pollution are more likely to be hospitalized for their condition. Why aren't we measuring trichloroethylene in the urine of dry cleaning workers. Trichloroethylene is also widely used as a degreaser. Why aren't we measuring that in their urine? Why aren't we doing whole-body studies of people with Parkinson disease? We know that these chemicals, for example trichloroethylene, also cause cancer. Could we find out that there are occult malignancies hiding out in the bodies of people with Parkinson's disease?

Why in postmortem studies aren't we measuring these chemicals? There are lots and lots of questions that we could be answering, but we just really haven't invested either the time and certainly not the resources to do so. We were mentioning earlier on about the difficulty getting NIH grants.

I wrote a grant to follow a cohort of people who were likely exposed to trichloroethylene because they worked in an office building next to a dry cleaner. Trichloroethylene, like radon, can evaporate from [00:20:00] the soil and enter your home, school, or workplace. And you would never know about it, and you could be developing Parkinson's disease years later after your exposure to indoor pollution of it.

And the reviewer said, "If trichloroethylene is as important as Dr. Dorsey says it is, why don't we know anything about it?"

Dr. Mitra Afshari: That ... sorry, that was... I, I can't follow that with a great question. But you really hit the nail on the head. I want to come back to research funding, like you mentioned, but one thing that really spoke to me in the paper also was the influence of sex on PD prevalence is such a big topic, and there's so many big question marks there.

What are more of your thoughts on that, specifically? Do you have a dominating hypothesis there in your mind, or do you think it's multifactorial just like many things are?

Dr. Ray Dorsey: Yeah, I think we got to get off this multifactorial thing. The job of neurologists, the job of doctors is to figure out what the causes of diseases are, full stop. Our job is to figure out the [00:21:00] cause of disease. If someone gets a stroke, we don't say " it's multifactorial," and then "gene-environment interactions" and move on.

No. We say, "Is it atrial fibrillation? Is it carotid artery disease? Is it small vessel ischemic disease? Is it valvular disease?" And we say what it is, we give an answer. We could be wrong, and it could be other factors in addition to it, but we come up with what the cause is. And when you find the cause, you can then prevent the disease.

And we've done that for stroke. And because we've done that for stroke, the incidence, the number of new cases of stroke in the United States today is 30% lower than it was in 1990. So I went to medical school, graduated in 1999. Since I basically have been in medical school, the incidence of stroke has decreased by 30% in the United States.

Kudos to our colleagues in stroke. But if we did that for Parkinson's, it would be the other. And I think that's a blight on us. So if you hear passion, something comes from Ray Dorsey, is I don't like failing. I don't like the fact that the Parkinson's community has failed to recognize that Parkinson's is one of the world's fastest growing diseases, and that the principal reason for the rise of Parkinson's disease is [00:22:00] not genetics, it's not aging, it's chemicals in our environment.

You put a mouse in the laboratory and you let it age, it will never spontaneously develop Parkinson's. It doesn't. The only way it develops Parkinson's is if you manipulate its genes or expose it to toxic chemicals or sometimes both. But if you take away the chemicals, the mouse is not going to develop Parkinson's. You take away chemicals, the vast majority of people with Parkinson's would not develop it.

Now, sex. Most studies of Parkinson's disease suggest that men are at greater risk of the disease than women. This has been repeated time and time again, and most studies suggest that the magnitude of difference is around 40%, 1.4 men for every 1 woman with the disease.

That said, that is not a uniform finding. There are studies in, I think it's Japan and Taiwan, where the incidence of Parkinson's disease is equal, or in one of those countries, I believe, it's even more women than men. I said to myself, how does this happen to be?"

Then I said, "Let me look at farmers in Japan and Taiwan." In the United States, [00:23:00] 75% of farmers are men. In Japan and Taiwan in the 1970s or '80s or so, someone will correct me if I'm wrong, it was equal if not more women than men. And if the principal route of exposure to the chemical in those countries would've been pesticides, DDT was widely sprayed in Japan on the rice paddies, and other organochlorines after World War II, then it would stand to reason that women would be as likely to develop the disease as not.

In the United States, where again, because clearly men are at higher risk, 97% of pesticide applicators are men. Most mechanics working with degreasing agents like trichloroethylene are men. Most groundskeepers, pesticide applicators are men. So I think the differences between male and female in the United States and in many parts of the world is principally sociology, not biology.

And that gives us another clue as to why the disease is occurring. If it were genetics, then it wouldn't have anything to do with sex. Now, [00:24:00] there are clearly biological factors. I'm not a laboratory scientist, but my colleagues, including one this morning, was telling me that it turns out that female mice or rats, I can't remember which, appear to be more resistant to these toxic effects . And so it could be that, too. I'm not discounting that. There are people who know far more about that than I do. But I'm moved that it's sociology, not biology, that are principal determinants in humans about who's developing the disease.

Dr. Mitra Afshari: I'm definitely with you on that end, Ray. I agree wholeheartedly. And I'm actually writing a paper about this as well. I think, we all want a cure to Parkinson's, but you've really made a great argument over the last few years that we need to shift our focus to prevention and really address the low-hanging fruit, if you will.

We lived through the COVID pandemic, and we found out that personal protective equipment, even when you can't get rid of an exposure, does indeed work. So where do we go from here?

Dr. Ray Dorsey: They're not mutually exclusive. Cure and prevention are not mutually exclusive. In fact, if you want to cure disease, the [00:25:00] prerequisite to curing a disease is to know what its cause is. I'm hard-pressed to think of a single disease that we can cure in medicine with medications where we don't know its cause.

I'll give you an example. Doctors have gotten lots of things wrong in the past, and I've gotten things wrong. I was taught in medical school that you could almost never get someone addicted to opioids who was in pain, right? We've clearly gotten things wrong in the past.

1960s, peptic ulcer disease, bleeding ulcers, a top 10 leading cause of death in the United States. People said that the principal cause of bleeding ulcers was stress. People needed to change their jobs. It was impossible to have bacteria growing in the acidic environment of the stomach. All generally nonsense.

And it turned out that the principal cause of peptic ulcer disease was H. pylori, a bacteria . The scientists who discovered this were widely ridiculed and dismissed for that. One of the scientists even went to the point of giving himself peptic ulcer disease by drinking the gastric juices of someone with peptic ulcer disease to show that it was a transmissible disease, an infectious disease.

And today, almost no one [00:26:00] dies of bleeding ulcers. Probably even when you were in training, you saw bleeding ulcers, a bloody mess in the emergency room. Now it's like bleeding ulcers just almost never happen. 'Cause we know the cause of disease, and the cure was an antibiotic and some acid-suppressing chemicals, and you cure the disease.

We did that with stroke. If we find out what causes stroke, whether it's AFib or valvular heart disease or PFOs or whatever it is, we can take action to prevent people from ever getting the disease. So if we want to cure the disease, I suggest that we first go and figure out what the causes of the disease are.

We have drugs in development for GBA PD and LRRK2 PD, but that affects less than 15% of people with the disease. What about the 85% who don't have LRRK2 mutations or don't have GBA mutations? Research by Dr. Ethan Brown and Dr. Caroline Tanner, again, showed that people who are exposed to pesticides and carry GBA1 mutation are more likely to develop Parkinson's disease.

GBA might explain why some people exposed to pesticides are more likely to develop the disease. GBA mutation, in and of itself, may have nothing [00:27:00] in terms of causing the disease. As far as I know, GBA mice don't develop Parkinson's disease. But mice exposed to paraquat do.

So the prerequisite to curing a disease is to find out its cause, and I think there's a little bit of hubris if we think we're going to cure disease where we don't take the first steps of trying to figure out what causes it. We figured out the cause of Huntington's disease.

We're developing gene-directed therapies against it. If you figure out the cause of it, you can cure it. I mean, MS, it seems to be pretty clear that it's Epstein-Barr virus. Dr. Alberto Ascherio of Parkinson's community showed that people who are exposed to Epstein-Barr virus are 30 times more likely to develop MS than people who aren't, and it might explain why some people with different HLA alleles are at greater risk for developing disease.

Those HAL allele differences may have nothing to do with causing MS in the absence of the Epstein-Barr virus, but they're just that variability in humans which makes us resilient from getting wiped out from any exposure to any one virus or any one pesticide or any one [00:28:00] bacteria, that those things are being exploited by new chemicals appearing in our environment, leading to new diseases like Parkinson's disease developing over the last two centuries.

Dr. Mitra Afshari: Thank you for clarifying, Ray. I could listen to you talk about this forever. This is really a wonderful kind of lesson in history. So this was really a wonderful discussion, a long-awaited discussion with you. There's no hotter topic than this, and it was really wonderful hearing all of your thoughts across the various topics with respect to environmental toxicants.

Dr. Ray Dorsey: Again, it's not environment. It's like, what are the causes of the disease? For stroke, we know what the causes of the disease are. The incidence is down 30%. For multiple sclerosis, we now know what the cause of the disease is. It's likely a virus for the vast majority of people with the disease.

We will now take action. Lots of therapies being developed to prevent. It could be vaccine therapies to prevent people from getting MS. We could say goodbye to diseases. Diseases are not permanent fixtures of society. Diseases come, and [00:29:00] diseases go. We've said goodbye to smallpox. We've largely said goodbye to polio.

We're saying goodbye to HIV. HIV is at its lowest level since the 1990s, and we've done that not because we cure HIV. I think only 5 people in the world have ever been cured of HIV. We do that by preventing the disease. We prevent it through a condom. We prevent it through highly effective treatments that prevent its transmission.

We can do the same thing for Parkinson's disease. The challenge for you, the challenge for me, the challenge for all of our listeners is that we should be the generation that brings about the fall of Parkinson's disease. If our colleagues can do that for stroke, if our colleagues are doing that for multiple sclerosis, why can't we do the same thing?

Two centuries of Parkinson's disease is enough. Let us now be the generation that says goodbye to the disease. We see early signs that the incidence of Parkinson's disease in countries that have banned paraquat, that have gotten rid of organochlorine pesticides, that have gotten rid of  trichloroethylene, that have improved their air quality,

three studies in Germany say that the incidence of Parkinson's [00:30:00] disease adjusted for age is falling. The fall of Parkinson's disease has begun. The fall of Parkinson's disease has begun in countries that have cleaned up their environment by addressing the root causes of the disease. Now, they weren't trying to address the root cause of Parkinson's, but they knew that these chemicals weren't good for human health.

And if we take action to do that, we can follow the Germans and create a world in the United States, a world in the rest of the Americas and Africa and Asia and Australia that no longer has this disease that, in the words of Michael J. Fox, sucks. Parkinson's disease sucks. It's our challenge, our job as Parkinson's specialists to bring about the fall of Parkinson's disease.

If we find out what the causes of the disease are, we can develop policies and actions and interventions to get rid of this disease and to be the generation that says goodbye to it. What greater achievement for a group of neurologists, a group of Parkinson's specialists, than it would be to say we got rid of a disease in our time and in our generation?

Dr. Mitra Afshari: And we'll end the podcast with that. That was wonderful, a call to [00:31:00] action, and I hope in both of our lifetimes we'll be able to see that. Thank you, Dr. Ray Dorsey, and goodbye for now.

Dr. Ray Dorsey: Thank you.