字幕列表 影片播放 列印英文字幕 On December 22, 1984, cow number 133 on a farm in England's Sussex county began displaying head tremors and a loss of coordination. It died a few months later on February 11, 1985, while other cows began showing similar symptoms. But it wasn't until September of that year when a government pathologist determined that cow number 133 died from spongiform encephalopathy, later called bovine spongiform encephalopathy (BSE) or, more commonly, mad cow disease. And it would take several more years until scientists on the Spongiform Encephalopathy Advisory Committee (SEAC) announced a possible link between the disease in cows and a similar disease in humans (announcement made on March 20, 1996), sparking numerous efforts to curb its spread, from banning British beef exports, to culling more than 4 million cows, to banning blood donations. While early predictions estimated the outbreak would kill thousands to tens of thousands of people, there have only been 231 human fatalities worldwide, the majority within the UK. However, in 2013, a study was published where researchers tested over 32,000 appendices from British people for the disease. And they worryingly found that 1 in every 2,000 people in the UK is carrying the abnormal protein that causes the disease but are not showing any symptoms. At least not yet. Because an estimated 31,000 people are still carriers of the disease, preventative measures like blood donation bans are still in place to avoid transmission. In the US, if you spent more than 3 months in the UK from 1980 to 1996, you can't donate blood. But as the pandemic rages on, blood shortages are dire. Hospitals are struggling to have enough on hand. And since the 90s, new blood tests have been developed, and general cautions in blood donations have advanced. So are these bans just overkill at this point, or are they still necessary? When BSE is transmitted to humans it's called variant Creutzfeldt-Jakob disease or vCJD. This is just one of four major types of CJD, which are classified by how it is contracted. In addition to variant CJD, there is sporadic CJD, the cause of which is unknown. However, it is the most common, though still extremely rare, affecting 1 or 2 people per million each year in the UK. Familial or inherited CJD occurs when someone inherits an abnormal protein gene from their parent. And Iatrogenic CJD occurs accidentally in the medical setting. One famous occurrence took place between 1958 and 1985 when thousands of children were injected with human growth hormone collected from deceased donors who were unknowingly infected with CJD. CJD altogether is an extremely rare but fatal condition. It's caused by an abnormal, infectious protein in the brain called a prion. Prions are misfolded proteins with the ability to transmit their misfolded shape onto normal variants of the same protein, inducing them to change their conformation as well, producing a chain reaction that propagates the disease and generates new infectious material. This is unique in the disease world. Before prions were discovered, it was believed that all pathogens, like bacteria or viruses, had to contain nucleic acids to enable them to reproduce - like DNA or RNA. The discovery of prions opened our eyes to a totally new mechanism of disease. And it is a particularly devastating one. Their misfolded shape creates brain damage which quickly worsens over time. Proteins are a very important part of our body's chemistry and are responsible for the structure, function, and regulation of our tissues and organs. They are large molecules made up of hundreds to thousands of organic compounds called amino acids, which are attached in long chains or strings. These strings then fold into a 3D shape. This “protein folding” is key, as each protein forms a specific shape that allows it to perform its specific function. But if a mistake occurs, they can misfold, or fold incorrectly, which is how an abnormal prion occurs. There are many diseases caused by misfolded proteins. These can lead to a loss of function, like in cystic fibrosis or Tay-Sachs disease, where one type of protein is misfolded and therefore can't do its job. They can also stick together and cause clumps or plaques which disrupt cell function. This is what scientists think may be the cause of neurological disorders like Alzheimer's and Parkinson's. The other way prions devastate the brain is by creating holes. The infectious prion responsible for CJD converts normal proteins into an abnormal state. As they build up, they cause brain cells to die, which releases more prions, and so on. In areas where brain cells are killed, holes are created that make the brain sponge-like. This type of brain damage causes symptoms similar to other neurological disorders, like Dementia. In variant CJD, typically psychological symptoms that affect a person's behavior and personality develop first. In a few months, neurological symptoms develop, such as problems with coordination, slurred speech, numbness, dizziness, and vision problems. Over time, symptoms worsen until the patient is bedridden, completely unaware of their surroundings, and can't communicate. The disease always progresses to death. It took some years of research to nail down just how BSE spread from cow to cow and from cow to humans. Eventually, they identified the source as their food, in both cases. At the time, cows were often fed the remains of other cows. So, if they ate infected meat, they too became infected. This led to a spread of BSE between cows, eventually reaching a peak infection rate in 1993 of 0.3% of the UK national herd. The answer: ban the feeding of meat-and-bone mix to farm animals. Likewise, humans who ate beef containing infected nerve tissue contracted vCJD. While, initially, it was thought that humans weren't affected by the disease, once it was made clear that they were, bans were quickly placed on British beef exports, cattle over a certain age were banned from the food chain, and at-risk cows were culled. But eating infected beef isn't the only way humans can get vCJD. And this is where the blood bans come in. There were four cases in the UK where a patient contracted vCJD after receiving a blood transfusion. Quickly, blood donation bans were put in place in countries like the U.S., Canada, Australia, where people who have spent several months in the UK in the 80s and 90s are not allowed to donate blood. This seems like a broad stroke to ban millions of possible donors from just 4 instances of blood transmission. But, for a long time, it's been necessary, because it's difficult to know for sure if someone has vCJD. There is no blood test that can simply tell you if you have it. Typically, a diagnosis is made by considering the patient's symptoms and through neurological tests like MRI, which could show abnormalities typical of vCJD. But even then, its not conclusive. The only way to confirm a diagnosis is by analyzing the patient's brain tissue, which can only be done after they have died. So scientists are aiming their sights here: if there was a way to test for vCJD in living patients, then the ban could, in theory, be permanently lifted. Because prion proteins are primarily found in the brain, they are hard to detect in blood. So, researchers have developed a method to amplify the prions in blood samples called “protein misfolding cyclic amplification” or PMCA. It works by taking advantage of the infectious prions' natural tendency to convert normal proteins into an abnormal state. They did this by combining healthy proteins with a small amount of infectious prions and agitating the mixture with sound waves. The sound waves broke up the chunks of infectious prions, helping them to meet and infect normal proteins. Studies have shown that this method can accurately detect vCJD in human blood samples and even distinguish it from other types of neurological disorders, including sporadic CJD. In a 2016 study, it was found to correctly identify those with or without the disease 100% of the time. It can even detect it in patients who aren't showing any symptoms. In another study published in 2016, their test detected vCJD prions in two patients 1.3 and 2.6 years before they began showing any signs of the disease. While these results are extremely promising, it is still early days. A clinically available blood test has yet to be released. Nevertheless, some scientists think its time to rethink the bans on blood donations, especially with the implementation of safety measures like leukoreduction, a process which removes white blood cells from blood, since white blood cells sometimes carry pathogens. Methods like this have already helped to change the donation regulations in many countries around those who are at high risk of sexually transmitted diseases like HIV and AIDS. Increasing the number of potential donors is even more of a priority with the current blood shortages caused by the Covid-19 pandemic. Since the pandemic began, there have been alarming shortages of blood supplies. For one American blood center, 31% of their locations have a one-day supply or less. Luckily, changes have begun. In 2019, the Irish Blood Transfusion Service lifted their ban, enabling some 10,000 individuals to now donate blood. And in 2020, the FDA lifted their ban on US military veterans who served in Europe, now allowing 4.4 million more people to donate. With more testing and trials, soon this catch-all ban should be lifted in the US, saving hundreds of thousands of lives with much needed blood. How we treat our farm animals invariably affects our own lives. Mad cow disease, swine flu, avian flu - many diseases of the modern age spread to us from livestock, and many diseases like this happen due to the poor and overcrowded conditions in which we keep these animals. Keeping the animals healthy, will in turn, keep us healthy - along with it being simply the right thing to do. Ending the practice of feeding COWS to OTHER COWS was a solid step in the right direction. But there are still a lot of other bad practices, like pumping them full of antibiotics, that need to come to an end. Helping in this endeavor are new technologies being rolled out around the world, like this silly robot named Astronaut, which is a fully automated milking system. It lets the cows decide when they want to get milked, with no human input required, along with cleaning the utter before the milking process. Being milked more often means the cows get sick less often, they get fewer infections, and thus need fewer antibiotics. To learn more about this elegant solution you should watch Milking Robots For Healthier Cows on CuriosityStream, a part of the European Inventor Awards series. All episodes in the series are overviews of cutting edge technology that is working to solve our most complicated problems. CuriosityStream is a streaming platform with thousands of high quality documentaries like this one. And now, CuriosityStream has partnered with us to offer an incredible deal. By signing up to CuriosityStream you now also get a subscription to Nebula. 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