Scott Knapper, a biochemist and vaccinologist at the University of Saskatchewan, can easily imagine humanity’s ultimate end-of-life disease. The plague spreads rapidly, but the progression of the disease is slow and subtle. With no immunity, treatment or vaccine to stop its progression, the disease will eventually find its way into nearly all of us and is spread through all types of body fluids. Eventually, everyone infected will die. Even our food and drinks are not safe. That’s because infectious agents are tough enough to withstand common disinfectants and the heat of cooking. It will become so prevalent that it infests our livestock and crops. “Imagine that ingesting a plant could cause a fatal, untreatable neurodegenerative disease,” Knapper told me. “Any food grown within North America is potentially lethal to humans.”
This nightmarish disease does not yet exist. But for inspiration, Knapper looks to a real disease in his lab, a deadly disease that is devastating North American deer, elk and other cervids. We only need to look at chronic wasting disease (CWD), a highly contagious neurodegenerative disease.
Half a century has passed since then. discovered In a captive deer colony in Colorado, C.W.D. More than 30 US states and 4 Canadian provinces, as well as South Korea and some European countries. The disease has been detected in some captive herds. over 90% personal. In the wild, “there are areas where more than 50 per cent of bucks are infected right now,” said Debbie McKenzie, a biologist at the University of Alberta. CWD then kills indiscriminately and gnaws the deer’s brain until it leaves a hole in the tissue. “This disease is out of control,” Dalia Abdelaziz, a biochemist at the University of Calgary, told me.
What makes CWD so scary is the infectious, misfolded proteins that are responsible for it called prions. Prion diseases, including mad cow disease, have long been known as a terrifying but little understood threat. And CWD is in many ways the “hardest” of them to fight, more transmissible and more prevalent than any other known one, says Marcelo Jorge, a wildlife biologist at the University of Georgia. told me. Scientists believe it is impossible to eradicate CWD. It will be difficult to even limit the damage, especially if it spills over to other species, which may include us. CWD is already a perfect example of how dangerous prion diseases can be. And its destructive power has not yet reached its ceiling.
Among the world’s known infectious agents, prions are an anomaly, more akin to zombies than living organisms. Unlike standard microorganisms (viruses, bacteria, parasites, fungi), prions are just improperly folded proteins and have no genetic material and cannot build themselves from scratch or build themselves into two. It cannot be cut into pieces. To reproduce, they simply find properly formed proteins that share a basic composition and transform them into unusual shapes by mostly mysterious means. And prions are difficult to protect against because they are slightly misshapen versions of molecules that our bodies naturally make. Even though diseases progress rapidly, the immune system codes them as benign and ignores them. “This is a whole new paradigm for infectious diseases,” Knapper told me. “It’s part of your own body, and it’s working against you.”
Still, we have managed to stop many prion diseases. coolOnce common in the highlands of Papua New Guinea, it was introduced through local burial cannibal rituals. After people stopped doing this, the disease disappeared. Mad cow disease (officially known as bovine spongiform encephalopathy) is include By culling infected animals and eliminating suspected sources of infection, Cattle feed made from infected tissue. Even scrapie, a highly contagious prion disease that occurs in sheep and goats, is restricted to livestock, making it possible to reduce the number of infected populations. breeding They aim for genetic resistance.
On the other hand, CWD is home to wildlife, many of which are migratory birds. And while most other prion diseases primarily affect the central nervous system, CWD “invades almost every part of the body,” Jorge said. The deer then transmit the molecules, often through direct contact. They excrete prions in their saliva, urine, feces, reproductive fluids, and even the velvet of their horns long before symptoms begin to appear. Candice Mathiason, a pathobiologist at Colorado State University, and her colleagues discovered that: Just 100 nanograms of saliva It can sow infection.her study suggest Deer can also pass prions in the womb From doe to growing fawn.
Deer too ingest Prions from the environment can have molecules that linger in soil, trees, and game food for years or even decades. A team led by UTHealth Houston biochemist Sandra Pritzkow found that: Plants can also take up prions from the soil. And unlike many microorganisms, which are easily invaded by ultraviolet light, alcohol, heat, and low humidity, prions are so structurally sound that they can withstand nearly all standard environmental attacks. In the lab, scientists blast equipment under extreme pressure and temperatures of about 275 degrees Fahrenheit for 60 to 90 minutes to remove prions, or use bleach in concentrations high enough to rapidly corrode meat. The work area must be soaked with sodium hydroxide or sodium hydroxide.
Infected deer are also frustratingly difficult to spot. This disease is usually Year The prion is fully expressed while it invades the brain and steadily destroys neural tissue. This molecule can kill you without you even knowing it. “This is not a disease that will kill the whole herd of deer around this watering hole,” Jorge told me. The deer move away from the herd. They forage at odd times. They become brave when we are around them. They drool and urinate more, stagger, and begin to lose weight. Eventually, they will be targeted by predators, frozen in cold weather, or simply starved. However, in any case, the disease is fatal. CWD has reduced deer numbers in many areas of North America. “There are certainly concerns that the local population will disappear,” MacKenzie told me. Researchers fear the disease could soon spread to caribou in Canada, endangering Indigenous communities that depend on caribou for food. Hunters and farmers are also losing vital income. Although it is unlikely that deer will become extinct, the disease is taking away habitat for major herbivores and food for their predators.
Laboratory experiments have proven that CWD. Competent Infection of rodents, sheep, goats, cattle, raccoons, ferrets, and primates. But so far, jumping into non-deer species does not seem to be occurring in the wild. People eat an estimated 10,000 CWD-infected deer each year, no human cases have been recorded. Still, laboratory experiments show that at least human proteins When expressed in micemolecular biologist Sabine Gilch of the University of Calgary, said they may also be susceptible to CWD.
And the more prions transmit and infect more hosts, the more opportunities they may have to infect organisms in new ways. Prions don’t seem to evolve as quickly as many viruses and bacteria, Gilch said. But “they’re not as static as we would like.” She, McKenzie and other researchers say a crowd of of CWD strain Each has its own tendency to spread between species. With so many unchecked infections and so many hosts, “this is like a ticking time bomb,” Dartmouth College biochemist Surachai Suttaporn told me.
The world is unlikely to be completely free of CWD. Even options to slow progress are currently limited. Infection research efforts depend on funding, researchers’ time, and local generosity. hunter For samples.Environmental cleanup continues Mainly experimental And it’s difficult to do on a large scale. No cure yet exists, but it is nearly impossible to administer them all at once. And while culling campaigns can be very effective, especially in areas where the disease is endemic, they often provoke a public backlash.
Deer that carry certain genetic mutations appear to be less susceptible to prions and progress to full-blown disease and death more slowly.But the reason is nothing for now It seems possible to completely block infection or completely suppress shedding, but extending lifespan may only prolong infection. “Once an animal is infected, the chances of it dying quickly are almost zero,” Abdelaziz said. Even if a stronger prion resistance is discovered one day, “it’s probably only a matter of time before prions start adapting,” Gilch says.
In theory, vaccines could help, and several research groups, including Knapper and Abdelaziz, have made breakthroughs in recent years in overcoming the immune system’s inertia in attacking proteins similar to those in the body. made significant progress. Some strategies attempt to target only problematic invasive prions.others are chasing Both prions and properly folded native proteinsVaccines can therefore play the dual role of ambushing infectious invaders and starving them of reproductive food. (so far, experimental animals When bred to lack the native prion protein, it appears to function just fine, but its function is still largely a mystery. ) In early trials, both teams’ vaccines showed produced hopeful Immune response of deer animals. But both teams are unsure how effective the vaccines are at curbing molting, how long that protection lasts, or whether these strategies work across cervid species. is still not completely understood. For example, one of Mr. Knapper’s vaccine candidates is Accelerate disease progression in moose.
Vaccines for wild animals difficult to deliver, especially in this case where multiple doses may be required. “You can’t just run around injecting every elk and deer,” Knapper told me. Instead, he and other researchers plan to incorporate a salty apple cider slurry into the formula, hoping wild deer will eat it with some regularity. . “The deer really like it,” he said.
However, if CWD vaccines are brought to market, they will almost certainly be the first prion vaccines to make it past the experimental stage. That could be a boon for more than just deer. Other prion diseases can spread from one species to another. Others may arise spontaneously. CWD is not, and never will be, the prion disease that most directly affects us. But for now, it’s the most urgent, and the thing we have the most to lose, and perhaps also the most to gain.