There is no vaccine for prion diseases
In recent years, scientists have called prion disease one of the most terrible potential threats to humanity. It is based on — The infectious agents prions, discovered in the middle of the last century, have an abnormal protein structure and are super-resistant to almost any environmental factors: they can withstand deep freezing, fire, and the action of various chemicals. The disease is fatal in 100% of cases.
Prions — culprits of chronic wasting disease (CWD), or zombie deer disease. And the other day a sensational study came out about two cases of this disease in people — hunters from the USA who ate venison. Have prions learned to be transmitted from deer to people and how does this threaten humanity? Should we expect an epidemic of prion diseases and how can we protect ourselves from infection? «MK» found out about this.
Photo: pansionat-greenday.ru
Prion diseases — one of the most frightening diseases. This is a special type of severe neurodegenerative human diseases that are caused by special pathogens: prions. Prions — proteins of tertiary structure, capable of “breaking down” and other proteins, causing damage to neurons and brain tissue, as well as nerve tissue. These protein molecules may be normal or they may be abnormal. From the moment a prion enters the body until the development of the disease, years, even decades, up to 50 years can pass.
Prion diseases are 100% fatal, incurable and highly contagious. Prions remain infectious agents even when diluted 10 million times. The human body does not know how to fight them. It does not produce antibodies, i.e. Humoral immunity does not work. Cellular immunity also does not work; lymphocytes do not attack prions, so the development of the disease is inevitable.
But until now, the methods of transmitting these diseases to people have been quite exotic (for example, it is believed that the Papuans from New Guinea received the disease by ritually eating the brains of deceased relatives). Prion diseases can be either infectious or hereditary. But no matter how the prion enters the body, it can cause infection to another person. Prions cause so-called spongiform encephalitis. Today, several human diseases are known that are caused by prions: Creutzfeldt-Jakob disease; Gerstmann-Straussler-Scheinker disease; Kuru disease (the same one that developed among the natives of New Guinea); familial fatal insomnia; Alper's disease. All of them are incurable. Perhaps Alzheimer's disease and Parkinson's disease are of a prion nature. The most common manifestations of prion diseases in people: progressive dementia, impaired vision, coordination of movements, speech, tremors, spontaneity of consciousness, aggression, a person loses his human appearance and stops walking.
However, until now there has not been a single fact indicating the possibility of transmission of prion diseases from animals to humans. And then the news came that two hunters most likely died from a prion disease, which had previously been recorded only in deer. This is CWD — transmissible spongiform encephalopathy: in other words, the brain turns into a sponge. Deer drool and then lose the ability to move and die.
In a number of US states, 25% of the wild deer population and 70% of farmed deer are infected with CWD. In addition, the disease also occurs in moose. Lethal outcome is inevitable. Before death, an infected animal manages to release many prion particles into the environment, which are extremely stable and can wait a long time for their animal. Most methods of neutralization and disinfection are ineffective in combating them. They do not die when boiled for 2-3 hours, withstand cold down to -70°C for several years, are insensitive to ultraviolet radiation and radiation, and are not inactivated when treated with formaldehyde.
The alarming case of the death of two hunters who were diagnosed with Creutzfeldt-Jakob disease (the nature of its occurrence is still unknown, and it develops spontaneously in about 1 in 2 million people) was reported by researchers at the University of Texas in a new article in the journal Neurology. Fellow hunters died of a rare disease one after another. But the strange thing is that the hunters ate deer meat from the same CWD-infected population. Scientists suggest that they could have received defective prions from venison, along with which prion disease was transmitted to them, but so far this is only a hypothesis. If it is confirmed, it will be possible to talk about the first patients infected with chronic wasting disease from deer.
What is known about prions today and what can we expect in the future, «MK» Victoria Doronina, a microbiologist and assistant at the Department of Science at the Faculty of Education at Manchester Metropolitan University, said:
— Prions were discovered in the 1980s by Stanley B. Prusiner, an American neurologist. Prusiner coined the term “prion,” which means “protein infectious particle,” to describe a unique infectious agent. His discovery challenged the traditional understanding of infectious agents because prions have no nucleic acid (DNA or RNA) and reproduce by causing normal proteins to misfold into the abnormal prion form. This discovery fundamentally changed our understanding of infectious diseases.
— Parasites are usually called living organisms, usually eukaryotic, i.e. having a core that live in the host’s body and weaken it. Bacteria — nonnuclear organisms that can be, depending on the species, either human symbionts or cause disease. Although they do not have a nucleus, they are complex organisms with cellular structures and a set of nucleic acids — DNA and several types of RNA. And finally, viruses — These are DNA or RNA molecules packaged in a protein shell. Viruses are inert until they enter the body, where they seize cell resources for their reproduction. In plants there are viruses without a protein shell — viroids, i.e. it is pure nucleic acid. For many decades, there have been philosophical debates about whether viruses are living organisms: the definition of a living organism includes metabolism and the ability to reproduce, viruses only have the latter.
Well, prions — these are pure proteins, and this is their main difference from all other types of infectious agents. Prions do not contain nucleic acid, and to reproduce in the sense of “reproducing on the basis of genetic material” they cannot, only convert an existing similar protein into another form.
Stanislaw Lem has a story about a robot who witnessed the death of astronauts after a spaceship accident, there is a phrase: “Who can survive death?” Only dead.» Prions cannot be called dead organisms because they were never organisms and were never alive. One might as well call the press that churns out parts at a factory a dead organism.
— Precisely because prions — a pure protein that is much more resistant to environmental conditions than nucleic acids, which are easily destroyed by ultraviolet radiation, even at low temperatures. Not only prions — these are proteins; prions — proteins in a very stable form, so-called. “beta sheet”, in which individual protein chains interact with each other. Individual molecules attach to each other, like Lego blocks, forming aggregates that are resistant both to cell attempts to pull them apart into individual molecules and restore their original shape, and to external physical influences. Therefore, prions cannot be destroyed by drying, surfactants, alcohol, formaldehyde, or even any autoclaving that combines high temperature and pressure. So prions can be transmitted during surgical operations. When I was working as a research fellow at the University of Manchester studying prions in yeast (not harmful to humans), we had DNA that allowed the production of human PrP (a prion) in yeast. But no one, including me, dared to use them, although theoretically, if you do not eat them, the possibility of infection is extremely low.
— I don't think they can be called vectors because vectors usually refer to the intermediate host that spreads the pathogen or virus. In the case of prions, the protein is already in the body and performs its functions until, as a result of mutation, it becomes a prion form. The protein that was identified as the first prion, PrP, is found in all mammals. It is also found in birds, amphibians and fish — i.e., it is likely present in all vertebrates, although it is less abundant and its functions have not been studied in non-mammals.
PrP— the first of the prion-forming proteins, but not the only one. Evidence is now accumulating that other human proteins that accumulate during Alzheimer's and Parkinson's diseases — tau and amyloid beta, — these are prion-like proteins. There is evidence of their transmission during the use of hormones and transplants that were taken from people with the disease. Many years after use, recipients developed early-onset Alzheimer's. Potentially, quite a large number of human proteins can become prions, but neurodegenerative diseases are caused by the prionization of proteins in the nervous system.
— Over the past few years, scientists have been monitoring the spread of a neurodegenerative disease caused by prions among deer and elk in North America. The difference between this prion and the previous ones is that it can be transmitted to animals through saliva. «Mad cow disease» was transmitted to people when they ate the meat of infected animals, and then through surgical instruments. But these sources are quite easy to isolate, and the epidemic of “mad cow disease” ended quickly in the 2000s. In deer, a healthy animal only needs to eat grass that has been exposed to the saliva of an infected animal.
In the first case of transmission of a deer prion to people, it appears that hunters ate the meat of a killed deer — deer steaks with blood. This is the same route of infection as “mad cow disease”. However, «mad cow disease» is not transmitted through saliva, it began to spread among livestock when animals began to be fed bone meal made from the remains of sick animals.
— There are two questions now: Can humans become infected with deer prion from contact with deer saliva? Can people infected by any means transmit the prion through their saliva?
If the answer to the first question is “yes,” we can expect infection not only among people who ate meat, but also among ordinary tourists who sat in the wrong place in the forest. If the answer to the second question is “yes” — this means that an epidemic of “deer rabies” may begin or has already begun, since symptoms appear after several years, during which time a person can infect many others.
— It depends on the answer to the questions above. Transmission through animal saliva to humans is not as dangerous as human-to-human transmission. The first can be compared with SARS — the precursor virus of covid, when the pandemic did not happen, the second — with COVID-19, where the virus is transmitted by airborne droplets. But unlike any viral diseases, there are no vaccines against prion diseases.
— There are some drugs developed against tau and beta-amyloid that slow the progression of the disease if started early enough. But these drugs have just received approval for use, they are expensive and do not cure, but only slow down the symptoms of Alzheimer's disease. The story with drugs against prion diseases is similar to the story with COVID-19 vaccines. After the wave of “mad cow disease” they began to be developed, but when the epidemic did not occur, they were simply abandoned.
— Start by banning the hunting and consumption of all deer and elk in North America. Ideally, they would also visit the forest to reduce the likelihood of infecting people with the saliva of sick animals, but this is already a quarantine, and people, as it turns out, really don’t like quarantines. And, naturally, we need to give money to scientists to study “deer rabies.”
In order to avoid prion diseases, drugs derived from animals (organic preparations) are prohibited in many countries of the world, because the causes of prion diseases are due to including the use of their biological tissues. Among such drugs – actovegin, solcoseryl, sirepar.
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