Syphilis, Rabies, Tetanus, Invasive Strep, Monkeypox, and Raw Meat: How Six Infectious Diseases Attack the Human Body

The first episode is about syphilis. Syphilis is a sexually transmitted infection caused by the bacterium Treponema pallidum, and in nature only humans contract it. Its symptoms change in stages over time, producing a wide range of lesions throughout the body. Rabbits have a very similar disease called "rabbit syphilis," but the video notes that it is a separate disease that does not infect humans. Syphilis has long been described as "the disease that makes your nose fall off," and the narration says this description is medically accurate.

As for its origins, the video introduces the well-known Columbian theory, which holds that syphilis came from the Americas. According to this theory, Indigenous peoples of the Americas in the 15th century already carried the causative bacterium but did not recognize it as a disease because they had immunity. Columbus and his crew came into contact with it and brought it back to Europe, where it spread among Europeans who lacked immunity. However, there are many counterarguments, and another theory holds that humans were already infected with syphilis somewhere between 16,500 and 5,000 years ago. The video says "the truth is still shrouded in darkness."

Syphilis declined after World War II, but according to the video it has been increasing rapidly since 2010. In the United States, the number of cases per 100,000 people rose from 40.4 in 2020 to 53.2 in 2021, a 31.7% increase in a single year. In Japan, the number of reported cases in 2022 reached 10,743 as of November 9. That is reportedly an increase of about 83% compared with 2020, and about 547% compared with 2014. The video attributes the resurgence to a change in transmission routes. Previously, most infections came from sex between men, but in recent years heterosexual transmission has been expanding. The infection rate from sexual contact with a patient who has been infected for less than a year is said to be about 30%, and the video warns that this is a serious threat for people whose lifestyles are somewhat reckless.

The video explains that Treponema pallidum has some highly unusual properties for a pathogen. The first is its slow growth. Whereas E. coli, which can also cause food poisoning, divides once every 20 to 30 minutes, Treponema pallidum takes more than 30 hours. Because its activity as an organism is so slow, it is reportedly hard for the human immune system to detect. The second is its lack of markers. It lacks lipopolysaccharide, a structure the immune system uses to recognize pathogens, and it constantly alters its outer membrane proteins, which are also immune targets, through mutation. The narration likens it to a "first-rate spy" who infiltrates enemy territory and destroys the organization from within.

Transmission occurs not only through ordinary intercourse but also through anal and oral sex. The progression of symptoms is explained in three stages. The first stage occurs a few weeks after infection, when a lump forms at the site of entry, such as the genitals, anus, or mouth. It is often painless and heals on its own, so people may not realize they are infected. In the second stage, over roughly three months, the bacteria multiply and spread throughout the body via the bloodstream. Small red rashes resembling roses appear on the palms, soles, and torso, which is why they are called "roseola." Fever, fatigue, headache, and loss of appetite may also appear. These subside on their own within a few weeks but reappear after some time. The video stresses that this cycle of recovery and relapse makes the disease seem less frightening, and that treatment must not be neglected at this stage.

The third stage occurs several years after infection, and reportedly 25% to 40% of untreated patients progress this far. The most conspicuous feature is soft, rubbery tumors. They form on the scalp, face, upper torso, legs, and elsewhere, and can destroy surrounding tissue. When one forms on the nose, it results in the nose "falling off." The disease can also cause cardiovascular damage, cognitive decline, and difficulty walking, and can be fatal.

Around the 16th century, when syphilis spread around the world, it was indeed a deadly disease. The video cites the lack of medical knowledge at the time as one reason. The dominant treatment then was mercury therapy, devised by Paracelsus, a physician who was also an alchemist. Because patients were treated by methods such as drinking highly toxic mercury, many developed mercury poisoning. There is reportedly even a saying: "A night with Venus, a lifetime with Mercury."

The turning point came in 1928. Penicillin, an antibiotic—that is, a chemical that selectively kills microorganisms—was discovered from a product of blue mold. Penicillin works well against Treponema pallidum and remains the first-line treatment for syphilis today. Thanks to this drug, also called a "magic bullet," deaths from syphilis are now very rare.

However, the video adds an important caution. Syphilis can be cured only when it is properly treated in the early stage of infection. With a disease whose symptoms come and go, stopping treatment on one's own judgment or avoiding treatment can lead to serious consequences not only for the patient but also for their partners. The narration concludes that because Treponema pallidum has survived to this day by remaining inconspicuous, it is wise to assume it is always close at hand.

The next episode is about rabies. Rabies is an infectious disease caused by the rabies virus, a zoonosis that infects not only dogs but all mammals, including humans. The virus is about 75 to 80 nanometers wide and 180 nanometers long, and shaped like a bullet. Rabies occurs when this virus invades the brain and spinal cord. Once it enters the central nervous system, the infected person develops delirium and paralysis, and in the end nearly 100% die.

The disease has a long history; the ancient Greek philosopher Democritus mentioned it. Aristotle also wrote that mad dogs transmit the disease to other animals. Today it occurs in most regions of the world, except for a few places such as Japan, the United Kingdom, and the Scandinavian countries. According to data published by the WHO in 2017, the estimated annual death toll is about 59,000, with 95% concentrated in Africa and Asia.

Rabies has already been eradicated in Japan. Although there have been a few cases of people infected abroad who developed the disease and died after returning home, the last domestic human case was in 1956. The video credits this to the Rabies Prevention Act, enacted in 1950, which made owner registration and annual vaccination mandatory, and to the thorough capture of stray dogs, and praises it as a public health success the country can be proud of before the world.

In Asia, dogs are the main source of infection. In some regions, bats, foxes, and other animals also transmit the virus. Infection occurs when an infected animal bites a person or another animal and saliva containing the virus enters the wound. Infected animals reportedly show signs such as not being afraid when people approach, being extremely agitated, or, in the case of nocturnal animals like bats, being active during the day. Such animals are hard to identify, but approaching them is the first danger signal for infection.

The video explains the course after a bite as follows. The virus first replicates to some extent in the muscle tissue at the bite site and may remain in that area during the incubation period. Meanwhile, it travels from the wound along the nerves, reaches the brain via the spinal cord, and begins multiplying in earnest there. It moves very slowly, about 3 millimeters per hour, and this period is the incubation period. It varies with the distance between the bite site and the brain, but is generally about 30 to 50 days, as short as 10 days, and in slow cases as long as a year. Once in the brain, the virus moves to the salivary glands and spreads into the saliva. This is why rabies is transmitted by bites.

There are two types of symptoms after onset. The first is the furious type, in which the patient becomes extremely agitated and hyperactive and is beset by hallucinations. Hydrophobia, in which merely seeing water makes the whole body tremble with fear, and aerophobia, a fear of drafts and fresh air, also appear. About 80% of rabies cases are reportedly of this type. The fear of water arises because attempting to drink water and various stimuli cause spasms in the muscles involved in breathing, such as those of the pharynx and larynx, and patients actually feel pain and distress just from seeing water. The second is the paralytic type, in which the patient becomes paralyzed without hydrophobia or aerophobia. In either type, the patient ultimately falls into a coma and dies.

The video highlights an interesting anatomical feature. Even though it is a disease that attacks the brain, patients' brain tissue shows no characteristic signs of nerve cell death. Studies using devices that examine brain function have also found no characteristic differences between the brains of furious and paralytic patients. From this, it is thought that the rabies virus does not destroy the brain but selectively disrupts only neural activity. The video says this gentle disruption may also be how the virus successfully evades the human immune system, and describes the virus as a "genius hacker of brain function."

There are cases of people surviving with experimental treatment even after the virus has reached the brain. That treatment is the Milwaukee Protocol. Based on the fact that the virus multiplies in the brain, it involves using drugs to deliberately put the patient into a coma to protect brain function until the human immune system starts working. However, according to the video, behind the successes there have also been serious side effects and failures, and objectively it cannot be called a reproducible method. In recent years, papers strongly criticizing this treatment have also been published. The video says the reality of rabies is that once the virus reaches the spinal cord and brain, it is over.

So is there nothing to do but give up once bitten? The video's answer is "no." Since the virus's full-scale multiplication and the onset of disease begin only after it reaches the spinal cord and brain, treatment is possible if the virus in the body can be eliminated during the incubation period while it slowly travels up the nerves. Specifically, the wound is first thoroughly washed with water and soap to reduce the amount of virus. Next, rabies vaccine is administered to activate the immune system and prevent onset. In addition, research continues into treatments for after the virus reaches the brain, using antibodies and antiviral drugs, and some successes have reportedly been achieved in animal and cell experiments. The video concludes that with appropriate measures based on accurate knowledge, treatment is possible even after the virus has entered the body.

The third episode is about tetanus. Tetanus is a disease caused by a microorganism called the tetanus bacterium (Clostridium tetani). This bacterium exists in a dormant state called a "spore" in soil, in the intestines and excrement of animals, and on rusty nails and barbed wire, and it is everywhere in our everyday environment. Bacteria in a state where they can grow and multiply are called "vegetative cells." Vegetative tetanus bacteria are vulnerable to heat, and the presence of oxygen is unfavorable to their survival. For this reason, in oxygen-rich places such as soil, they lie quietly dormant as spores.

However, when someone is injured, the wound is contaminated with soil or the like, and spores enter the body, the bacteria wake up. The bacteria produce a protein toxin, which attacks the central nervous system and the sympathetic nervous system. As a result, the muscles throughout the body contract, stiffen, and spasm, and in the worst case breathing stops and the patient dies. The spread of effective vaccines has greatly reduced deaths, but tens of thousands of people still die of tetanus each year, and the video says its status as a latent enemy of humanity has not changed.

The oldest record of tetanus dates back to Egypt in 1500 BC. In ancient Greece, Hippocrates, known as the "father of medicine," recorded its symptoms and also discussed the need to disinfect wounds. The video praises this as forward-looking in terms of thinking about prevention and treatment. In 1884, it was shown that tetanus could be transmitted by inoculating rabbits with pus from infected patients, and in the same year that it could also be transmitted by contaminated soil. The decisive advance came in 1889 from Kitasato Shibasaburo of Japan. Kitasato succeeded in growing a pure culture of the tetanus bacterium, proved its pathogenicity in animal experiments, and reported that the toxin produced by the bacterium could be neutralized by specific antibodies. Later, in 1924, a vaccine called tetanus toxoid was developed.

The video explains that spores are extremely stable and are not killed by freezing, ethanol, or household disinfectants. The bacterium dislikes oxygen, but the inside of a wound is low in oxygen, an environment favorable to its growth. When spores enter a wound, this serves as a signal for them to germinate, and the bacteria grow and multiply. At the same time, they begin producing a protein toxin called tetanospasmin.

This toxin binds to the neuromuscular junction, where the ends of motor nerves connect to muscles. Then, over about 2 to 14 days, it travels back along the nerve cells to the anterior horn of the spinal cord, and further to the parts of the brain that control movement. At multiple sites—the neuromuscular junction, the spinal cord, the brain, and the sympathetic nervous system—the toxin blocks the release of glycine and GABA, which are inhibitory neurotransmitters. As a result, excitatory signals keep flowing unchecked, causing muscle spasms.

The most common form is generalized. In the early stage, the jaw seems to lock up, making it difficult to open the mouth. Eventually the stiffness spreads throughout the body, the back muscles contract strongly, and the back, neck, and legs arch backward, bending the whole body like a bow. The facial muscles also stiffen, producing a grimacing expression. Swallowing food becomes difficult, and the abdominal muscles also stiffen. Spasms lasting several minutes may wrack the entire body. Because spasms are triggered by external stimuli such as noise, light, and physical contact, patients live in fear of stimuli from the outside world. The stiffness and spasms are painful, and in severe cases numbness and pain spread throughout the body, and paralysis of the respiratory muscles can cause suffocation. There are also localized forms, in which muscle spasms are limited to the area near the wound, and cases where the cranial nerves of the face are affected, but these are reportedly rare.

Without appropriate medical care, the fatality rate approaches 100%. In developed countries, where vaccination is the norm and treatment methods are established, the fatality rate with appropriate medical care is said to be about 10% to 20%. However, in some countries and regions, appropriate medical care itself is not widely available. Tetanus is still said to affect 73,000 people and kill 34,000 worldwide each year.

The key to prevention is the vaccine. According to the video, tetanus toxoid provides very long-lasting immunity, and some studies suggest a single dose may remain effective for as long as 72 years. In Japan, the tetanus vaccination rate for children in fiscal 2022 was 91.8%. Currently, about 100 people develop tetanus in Japan each year and around 5 to 9 die, but most of those who develop it were reportedly born before 1968, when vaccination was not yet widespread. The video presents this as a fact that demonstrates the importance of vaccines. The remaining challenge, the episode concludes, is how to spread this established method of prevention around the world.

The fourth episode covers an infectious disease that was reported in the first half of 2024 as "flesh-eating bacteria cases hit record high." Medically, it is called streptococcal toxic shock syndrome, a disease in which group A Streptococcus destroys the body. It is called "flesh-eating bacteria" because the infected area becomes necrotic and turns black, looking as if it had been eaten. The bacteria themselves are shaped like round beads strung together, which the video describes as "like a botched Pon de Ring doughnut."

This bacterium is very familiar, living even in the throats, digestive tracts, and skin of healthy people. In most cases it is not a major threat, and if it multiplies in the throat, it causes no more than pharyngitis. In one example, it was detected in 37% of children with sore throats, making it a common infection. However, when it enters places outside its usual habitat, such as the blood, muscle, or fat, the situation changes completely, and it dissolves the body while claiming lives at a high rate. According to the video, the fatality rate is 30%, and more than 500,000 people die from this bacterium every year.

The increase in Japan is striking. According to a report from the National Institute of Infectious Diseases, the number of patients in 2024 reached 977 by June 2, 2.8 times the 349 in the same period of the previous year. Since the previous year's total was 941, the number in half a year exceeded the entire previous year. As for how the bacteria enter the blood and elsewhere, routes through wounds and the possibility of droplet transmission have been pointed out, but much remains unclear. Because the bacterium is so ubiquitous, it is reportedly extremely difficult to identify the routes of infection.

Even when the immune system tries to eliminate the bacteria that have invaded the body, it does not always succeed. The video gives two reasons.

The first is the sheer number of "weapons" the bacterium has. Its means of destroying the body's defense systems can be divided into at least 17 categories based on current knowledge alone, and they act in a variety of places. Examples introduced include cleaving antimicrobial peptides to disable defense mechanisms, cleaving chemokines to prevent white blood cells from gathering, and inhibiting the differentiation and proliferation of T lymphocytes. The video says it is enough to understand that the bacterium has an abundance of specialized weapons for breaking through the body's many defense mechanisms one by one.

The second is that it exploits pain, the body's danger-detection system. People learn about abnormalities in their bodies through pain. Group A Streptococcus produces a toxin called streptolysin S during infection, and experiments in mice showed that this substance stimulates specific pain-related neurons to cause intense pain. Normally, pain should serve as the signal to start an immune response. However, this toxin causes the pain-related neurons to release a chemical that interferes with communication with the immune system, and that substance suppressed the mice's immune response and helped the bacteria multiply. Applying this to humans, the video says intense pain would not lead to rescue but would merely be evidence that the bacteria are multiplying efficiently.

After that, the bacteria produce virulence factors such as streptolysin and M protein, which damage tissue by destroying cells directly and indirectly and by causing inflammation. They also produce special antigens called "superantigens," which cause the immune system to run out of control. In the video's summary, this bacterium is not eating people; it is merely pressing the switches of the human immune system over and over. The out-of-control immune system ends up causing the body to injure itself. The infected area becomes necrotic and blackened, and when the bacteria circulate through the body via the bloodstream, damage spreads to various parts of the body within tens of hours of onset. This leads to multiple organ failure and shock, and in the worst case, death.

As for whether it could become a pandemic like COVID, the video says "it seems safe to rest easy for now." The main routes of infection are presumed to be droplet and contact transmission, and it is not as contagious as the airborne coronavirus. The increase is occurring in countries such as the United States, Japan, France, Ireland, the Netherlands, Sweden, and the United Kingdom, and it is reportedly not happening simultaneously across the entire globe. As countermeasures, the video lists the masks, gargling, and thorough hand hygiene learned in the fight against COVID, along with washing and disinfecting wounds when injured. It then recommends seeing a doctor promptly if there are any abnormalities such as fever.

The fifth episode is about monkeypox, which was reported to be spreading worldwide in May 2022. The video says many people must have felt anxious, since it was in the midst of the COVID pandemic and the virus was reported to be a close relative of smallpox. It then says what is needed is not panic but scientifically accurate information and an understanding of the current situation.

Monkeypox is an infectious disease caused by the monkeypox virus of the genus Orthopoxvirus, which also includes the smallpox virus. It got its name because it was discovered in laboratory monkeys at a Danish research institute in 1958, but the video cautions that monkeys are victims just like humans, and that thinking of them as the source of infection is a misunderstanding. The first human case was in 1970. It was originally endemic to the forest regions of Central and West Africa, and infections elsewhere were extremely rare. From 2018 to 2021, only eight cases were confirmed outside Africa, and all had a history of travel to Africa.

The virus's hosts are thought to be rodents such as squirrels and rats. Infection appears to occur through bites from these animals or contact with their excrement. As a reference, the video introduces a 2003 outbreak in the United States. Rodents imported from Ghana to Texas carried the virus and infected prairie dogs at a pet dealer. Those prairie dogs were sold as pets, leading to infections in 71 people.

The symptoms progress as follows. The incubation period is 7 to 14 days, during which the virus continues to multiply in the body. First, fever, headache, swollen lymph nodes, and muscle aches last for 1 to 5 days, followed by small red rashes. The rash often starts on the face and spreads to the arms and legs, and may cover the whole body. The rash eventually turns into blisters, which fill with pus, finally form scabs, and heal in about 2 to 4 weeks. The symptoms closely resemble those of smallpox, but the fatality rates differ greatly. Whereas smallpox has a fatality rate of about 30%, monkeypox's is from a few percent to 10%. The smallpox vaccine is also effective in preventing monkeypox, with a reported efficacy of about 85% in preventing onset. For these reasons, the video considers monkeypox not to be as great a threat as smallpox.

Even so, the video points out that the 2022 outbreak had several abnormal features.

The first is a new route of person-to-person transmission. In 2018, a hospital-acquired infection was reported in the United Kingdom, but it was a very rare case. On May 7, 2022, the first case of the current outbreak was reported, also in the United Kingdom, and by June 5 the number of reported infections in the UK had reached 302. Many of those infected had in common that they were men who had sex with men, such as gay or bisexual men. However, the video clearly states that this does not mean sex between men is dangerous. It is merely one example showing that the virus can spread from person to person through close contact involving skin contact, and it is more natural to assume that it is also transmitted through heterosexual intercourse. According to a WHO report, as of the end of May, 550 infections had been confirmed in more than 30 countries.

The second is the virus's genetic information. According to a report from Portugal's National Institute of Health, the virus in the current outbreak is estimated to have had a single source, and moreover, its DNA had more mutations than expected. The video says a new variant may have spread from one place to the rest of the world. On the other hand, it dismisses conspiracy theories that regard this as bioterrorism, saying there is no evidence and that they could even be called malicious fake news that needlessly stokes fear.

As for the possibility of a pandemic, the video cites two differences from COVID. The coronavirus is an RNA virus, and RNA is prone to mutation. This is why variants such as Delta and Omicron emerged one after another, fueling the spread of infection. The monkeypox virus is a DNA virus, which mutates less readily than RNA, so variants that trigger outbreaks should also be less likely to emerge. In addition, whereas COVID spreads through droplets from coughing and the like, monkeypox spreads mainly through close physical contact. Based on these points, the video considers the possibility of a COVID-scale pandemic to be very low. Humanity achieved complete victory over smallpox more than 40 years ago, and the experience accumulated in the fight against COVID should also prove useful in this response—that is the episode's conclusion.

The final episode is "What happens if you eat raw meat?" The video first establishes the premise that humans can eat meat raw if it is not contaminated with dangerous microorganisms, parasites, viruses, and the like, and then focuses on contaminated raw meat. Carnivores such as wolves and lions can eat raw meat without problems, but when humans do the same, there is a high probability of food poisoning from pathogenic microorganisms and other causes. The video says this difference looks simple but is actually a difficult question.

The reason carnivores are fine can be explained by the pH of their stomach acid and its barrier function. The stomach acid of typical carnivores is around pH 2.2, and that of scavengers that eat rotting meat is about 1.3 to 1.8; the strong acid kills pathogenic microorganisms and parasites. However, human stomach acid is about pH 1.5, comparable in strength to that of scavengers. It is considerably more acidic than that of typical omnivores, at around pH 2.9. Yet humans still cannot eat raw meat, so the barrier function of stomach acid alone cannot explain it.

The video suggests differences in immunity and gut environment between humans and wild animals as possible reasons. It also raises the possibility that carnivores basically eat only fresh meat, which has a low level of contamination, whereas humans eat meat some time after slaughter, which is more contaminated. The video admits that there are too many candidates and that it is nonsensical to narrow the answer down to one; it can only be considered the result of complex, intertwined factors.

Human ancestors are said to have begun cooking with fire 1.8 million years ago, in the era of Homo erectus. Because cooked meat is easier to eat and digest than raw meat, caloric intake increased greatly from this era onward, which triggered the evolution of larger, smarter brains. The video says it is highly likely that, through cooking, humans evolved their bodies from a "raw-meat-adapted type" to a "cooked-food-adapted type."

The symptoms of eating contaminated meat raw vary depending on the pathogen. So the video takes up Campylobacter food poisoning, which has been increasing in recent years, as an example. It is caused by the bacteria Campylobacter jejuni and Campylobacter coli, and occurs frequently from eating raw chicken, but also from undercooked beef and pork. In Japan, there are about 300 outbreaks a year, with around 2,000 people infected. After infection, diarrhea, abdominal pain, fever, vomiting, and other symptoms appear within about 2 to 5 days and last about 3 to 6 days. Except among the elderly and children, death is rare.

However, the video says it is premature to judge it as no big deal. That is because Guillain-Barré syndrome can occur as a complication of this food poisoning. It develops at a certain rate several weeks after infection is established; among Campylobacter jejuni infections in the United States, the rate was 1 in 1,058 cases. It is a type of autoimmune disease in which the immune system, which should be fighting the food-poisoning bacteria, attacks the body itself. Muscle weakness, tingling, and loss of sensation first appear in both legs, then spread to the arms, head, and the whole body, and the peripheral nerves are damaged. Patients may become unable to walk or may need a ventilator due to breathing difficulties. Symptoms peak in 3 to 4 weeks. The overall fatality rate is low, at about 2%, and most patients improve greatly within a few months. Even so, about 30% of adult patients still have mild muscle weakness three years later. The video says that even with a low incidence, this is far too great a risk as the price for eating raw meat, and that avoiding eating contaminated meat raw is an absolute rule.

The video ends with a thought experiment for viewers. Condors, birds that eat carrion, take in a variety of microorganisms living in dead meat every time they eat. Most of them are killed by the condor's strongly acidic stomach acid and powerful digestion. However, only microorganisms of the genera Clostridium and Fusobacterium break through this barrier and reach the intestines. Research suggests that these may contribute to the digestion of carrion while driving out other pathogenic microorganisms in the condor's gut. In other words, the research suggests that condors, through their unusual diet of carrion, may have formed a kind of cooperative relationship exclusively with extremely tough microorganisms.

Here the video returns to where it began. The acidity of human stomach acid is on par with that of scavengers that eat rotting meat, which can be restated as a barrier capability as strong as a condor's. Then what would happen to the human gut if a person kept up a diet of nothing but carrion for a long time, like a condor? The video hypothesizes that someday human gut bacteria might also be replaced by Clostridium and Fusobacterium, and humans might evolve into "condor-type superhumans" able to eat not just raw meat but even rotten meat. However, it admits that the likelihood is "very, very low." Even so, it jokingly suggests it might be worth trying with the help of the channel's character, Mr. VAIENCE, and the video ends.