This Devastating Disease Turns Your Brain Into a Sponge

<p>If you’ve watched HBO’s hit show The Last of Us, you’ll know just how terrifying an aggressive pathogen can be. While that fictional world covers fungal parasites rotting people’s minds and turning them into violent creatures, prion diseases and their devastating effects aren’t a million miles away. </p> <p><strong>What are prion diseases? </strong>Bacteria, viruses, and fungi are the first things that come to mind when we think of infections, but prion diseases work differently. They are caused by proteins called prions that become misfolded and have the potential to induce normal variants of the same proteins to misfold as well. This can lead to cascading devastation that ends in brain damage and death.</p> <p><strong>How do prion infections work? </strong>What distinguishes prions from other pathogens is that they don’t carry genetic material like DNA or RNA. Normal prion proteins (that aren’t misfolded) are found in healthy people and form part of several functions throughout the body, especially the nervous system. </p> <p>When these prions become misfolded, they are resistant to degradation and tend to accumulate in the brain, where they cause mayhem by disrupting cellular functions and triggering neurodegeneration. Under the microscope, an infected brain often shows holes that make it look like a sponge.</p> <figure><img alt="Pathology in CWD-Infected Animals | Source: Joel C. Watts, Aru Balachandran, David Westaway/Wikimedia" class="img-responsive" src="https://cdn.storymd.com/optimized/Wdx4Ogted2/thumbnail.jpg" /> <figcaption>Pathology in Prion-Diseased Animals Showing Spongiform Changes. <em>Source: Joel C. Watts, Aru Balachandran, David Westaway/Wikimedia</em></figcaption> </figure> <p><strong>Should I run into a bunker and hide? </strong>No. Our saving grace is that these diseases primarily affect deer, elk, moose, and other hoofed creatures, and widespread transmission among humans is not yet a problem. The most famous prion disease is chronic wasting disease (CWD), which is an increasingly common sight among deer populations. </p> <p>Prion diseases spread among animal populations through fluids like feces, blood, saliva, or urine, or direct contact with contaminated soil, food, or water. </p> <p><strong>How does CWD affect animals? </strong>CWD is a cruel and fatal disease for which there are no treatments or vaccines. It slowly turns these poor creatures into wretches before finishing them off. The incubation period can be over a year before symptoms like these show up:</p> <ul> <li>Severe weight loss (wasting)</li> <li>Poor coordination</li> <li>Stumbling</li> <li>Lethargy</li> <li>Drooling</li> <li>Excessive thirst or urination</li> <li>Drooping ears</li> <li>Being unafraid of people</li> </ul> <figure><img alt="Deer with chronic wasting disease | Source: Terry Kreeger, Wyoming Game and Fish and Chronic Wasting Disease Alliance./Wikimedia" class="img-responsive" src="https://cdn.storymd.com/optimized/Oo5aj03UDo/thumbnail.jpg" /> <figcaption>Deer With Chronic Wasting Disease. <em>Source: Terry Kreeger, Wyoming Game and Fish and Chronic Wasting Disease Alliance/Wikimedia</em></figcaption> </figure> <p><strong>Have people gotten CWD? </strong>To date, no cases of CWD have been reported in humans, but animal studies have pointed to the idea that CWD poses a risk to certain primates like monkeys that eat meat from CWD-infected animals or come into contact with fluids from infected deer or elk.<br/> <br/> This has raised concern over the possibility of CWD transferring to humans, and the WHO has pushed to keep all sources of meat potentially contaminated with prion diseases out of the food supply. In a 2022 paper, Canadian researchers found that CWD may be more transmissible to people than we previously thought.</p> <p><strong>Other types of prion diseases.</strong></p> <ul> <li><strong>Mad cow disease and vCJD. </strong>Bovine spongiform encephalopathy (BSE) (AKA “mad cow disease”) is a famous prion disease that has required the culling of entire herds to eliminate outbreaks, causing huge economic impacts on countries internationally. The disease is a relative of scrapie in sheep and goats as well as CWD.<br/> <br/> Mad cow disease taught us that prion diseases can hop the transmission barrier from animals to humans. During the BSE crisis, it was discovered that the infection could be transmitted to humans through contaminated meat, causing a new form of human prion disease called variant Creutzfeldt-Jakob disease (vCJD). <figure><img alt="Cow with BSE | Source: Dr. Art Davis/Wikimedia" class="img-responsive" src="https://cdn.storymd.com/optimized/1dm9wbfLdp/thumbnail.jpg" /> <figcaption>Cow with BSE. <em>Source: Dr. Art Davis/Wikimedia</em></figcaption> </figure> </li> </ul> <ul> <li><strong>Creutzfeldt-Jakob disease and its variant. </strong>vCJD is an offshoot of the regular version of Creutzfeldt-Jakob disease (CJD). vCJD has different clinical and pathologic characteristics and a distinct genetic profile. Both are invariably fatal brain diseases with long incubation periods.<br/> <br/> CJD is an extremely rare disorder with an estimated yearly incidence of one in a million. Unlike vCJD, it is not related to mad cow disease. Most CJD cases are sporadic and strike around the age of 60. <figure><img alt="MRI of a 46 year old with iatrogenic CJD Creutzfeldt–Jakob disease | Source: Peter Rudge,c Zane Jaunmuktane,Peter Adlard, Nina Bjurstrom, Diana Caine, Jessica Lowe, Penny Norsworthy, Holger Hummerich, Ron Druyeh, Jonathan D. F. Wadsworth, Sebastian Brandner, Harpreet Hyare, Simon Mead, and John Collinge/Wikimedia" class="img-responsive" src="https://cdn.storymd.com/optimized/LA1a7PHQA5/thumbnail.jpg" /> <figcaption>MRI of a 46 year old with iatrogenic CJD Creutzfeldt–Jakob disease. <em>Source: Peter Rudge, Zane Jaunmuktane, Peter Adlard, Nina Bjurstrom, Diana Caine, Jessica Lowe, Penny Norsworthy, Holger Hummerich, Ron Druyeh, Jonathan D. F. Wadsworth, Sebastian Brandner, Harpreet Hyare, Simon Mead, and John Collinge/Wikimedia</em></figcaption> </figure> </li> <li><strong>Gerstmann-Sträussler-Scheinker disease (GSS)</strong>. This disease happens at earlier ages (35 to 55) but is extremely rare. It is almost universally inherited and therefore found in only a select few families worldwide.<br/>  </li> <li><strong>Kuru</strong>. A very rare disease found in people from New Guinea. It's caused by consuming human brain tissue contaminated with infectious prions. This happened due to local funeral rituals that involved a form of cannibalism which ended in 1960 because of increased awareness about the disease and how it is transmitted.<br/>  </li> <li><strong>Fatal insomnia.</strong> A rare and mostly hereditary disorder that causes sleeping issues. </li> </ul> <p><strong>Symptoms of prion diseases in humans.</strong></p> <ul> <li>Rapidly developing dementia</li> <li>Walking issues including changes in gait</li> <li>Hallucinations</li> <li>Stiffness</li> <li>Confusion</li> <li>Tiredness</li> <li>Difficulty speaking</li> </ul> <p><strong>Risk of transmission to humans. </strong>Following the BSE crisis, strict measures were put into practice to prevent its spread. Concerns remain about further transmission taking place or new prion strains emerging.<br/> <br/> Besides contaminated meat, another reported mode of transmission is through medical procedures involving contaminated instruments. CJD has reportedly transferred during corneal transplants, and also via pituitary-derived human growth hormones and gonadotrophin hormones sourced from cadavers.</p> <p><strong>Prevention and research. </strong>Preventative measures aiming to curb prion transmission include strict regulations on animal feed production, surveillance programs for animals and humans, and rigorous sterilization protocols for medical equipment.</p> <p>Research efforts are underway to figure out the molecular pathways involved in prion propagation, identify biomarkers for early disease detection, and develop therapies that could stop or delay disease progression. Drug development, immunotherapy, and gene editing techniques are all being examined as part of the research.</p> <h2>More on Prion Diseases</h2><ul><li><a href="https://soulivity.storymd.com/journal/xjn6gkvhrw-prion-diseases" target="_blank">Prion Diseases: Types, Causes, Treatment</a></li><li><a href="https://soulivity.storymd.com/journal/4m8g24d0pw-bovine-spongiform-encephalopathy" target="_blank">Bovine Spongiform Encephalopathy (Mad Cow Disease): Causes, Transmission</a></li><li><a href="https://soulivity.storymd.com/journal/oja4e4li4j-chronic-wasting-disease" target="_blank">Chronic Wasting Disease (CWD): Causes, Transmission, Symptoms</a></li></ul>