Carl Zimmer reads books on Phoenix.com.
In this paper, the discovery history of five kinds of germs that have been raging and spreading wildly in human beings is discussed, including HIV virus, West Nile virus, Ebola virus, SARS virus and MERS virus. What needs to be known is that although the greatest scientists in the world are still engaged in medical research intensively and have put forward many effective measures to suppress it, even if human beings are expected to completely eliminate these diseases, it is not yet. What we can do is to take the initiative to understand it.
01
HIV virus
From October 1980 to May 1981, five men in Los Angeles, USA, were admitted to hospital for the same rare pneumocystis carinii pneumonia.
This kind of pneumonia is caused by Pneumocystis carinii fungus, its spores are everywhere, and most people have inhaled it into the respiratory tract at some point in their childhood. But people’s immune system will quickly kill these fungi and produce antibodies to protect their owners for life. However, if this person’s immune system is weak, Pneumocystis carinii will get out of control, and the patient’s lungs will be filled with fluid and scarred. Pneumocystis carinii pneumonia patients have difficulty in inhaling enough oxygen, so it is difficult to survive. However, the symptoms of these five patients are not typical-they are all young men who were in good health before suffering from pneumonia.
At that time, no one knew that these cases would quickly evolve into the most horrible epidemic in contemporary history. In fact, all patients have immune dysfunction at the cellular level, and the initiator is human immunodeficiency virus (HIV), which is HIV. Later researchers discovered that this virus has been quietly infecting humans for 50 years. Since their discovery in the 1980s, they have continued to infect 60 million people and killed half of them.
HIV virus
HIV is well-known, but it is not contagious, and people are not easily infected with AIDS. Even if the patient sneezes next to you or even shakes your hand, you won’t be infected. HIV can only be transmitted through certain kinds of body fluids, such as blood and semen. Therefore, unprotected sex will spread the virus, and people will be infected if they lose blood contaminated by the virus; If expectant mothers are HIV carriers, they may also transmit it to unborn children; Some heroin addicts share needles with others. If others are AIDS patients, the virus is likely to enter his body through contaminated needles.
Once HIV enters the human body, it will attack the human immune system. Its target is an immune cell named CD4. When the virus gene and protein manipulate and gradually take over the whole host cell, these cells can be used to replicate more HIV viruses and infect more cells. At first, the number of HIV virus in the human body will increase rapidly, but once the immune system recognizes the infected cells, it will start a desperate blow, and the infected cells will be destroyed by the autoimmune system, and the number of viruses will decrease. At this time, the patient will feel that he has only a slight flu. The immune system can successfully wipe out most HIV viruses, but a small number of viruses will survive quietly and hide in CD4 cells to continue to grow and divide. They are calm as usual most of the time, and occasionally wake up again, releasing a wave of viruses and infecting more cells. Although at this time, the immune system will rush to suppress the sudden small attack, but repeated many times, the immune system will eventually be exhausted and completely collapsed.
The time of immune system failure varies from person to person, which may take only one year or as long as 20 years. But no matter how long this process takes, the day will come: the patient’s immune system can no longer do its job, and those diseases that could not harm healthy people will become fatal. In the early 1980s, a large number of patients with suspected pneumocystis carinii pneumonia flooded into hospitals, in fact, they were all infected with HIV.
In this way, before finding the virus, the doctor first saw the power of HIV. They named the disease Acquired Immunodeficiency Syndrome (AIDS) for short. In 1983, two years after people first observed AIDS patients, a group of French scientists really isolated HIV from patients, and more studies also confirmed that the source of AIDS was HIV. But at the same time, in the United States and other countries, AIDS cases have emerged one after another, and in just a few years, it has become a global killer, and it has also become a mystery in the field of epidemiology.
It took scientists 30 years to figure out the root cause of AIDS-
In 1985, scientists tried to add HIV antibody to the serum of monkeys with similar symptoms, and as a result, they actually "fished" a new virus, which was named monkey immunodeficiency virus, or SIV for short. Scientists concluded that HIV may have evolved from one of the SIV viruses, but which one was unknown at that time.
In 1991, a scientist found a virus very similar to HIV in mangabey, West Africa. Later, new research showed that HIV was not of a single origin, and scientists divided it into two types, named HIV-1 and HIV-2 respectively. Among them, HIV-2 evolved independently from SIV virus carried by mangabey, and the source of HIV-1 is still confusing.
But HIV-1 is the main culprit of AIDS, and it took longer to find out the source of HIV-1. Relevant researchers have divided all the HIV-1 viruses in the world into four groups, among which 90% of AIDS is caused by M group virus, and other virus strains belong to N, O and P groups respectively, with a small number. After long-term research, it was not until 2015 that the life experiences of all four groups of HIV-1 viruses were settled. They came from Cameroonian gorillas mainly living in African forests.
Obviously, when scientists discovered HIV in 1983, the virus had become a potential global disaster; When scientists finally started to fight back, the virus had already occupied the first-Mover advantage. In the 1980s and 1990s, the number of people who died of AIDS kept rising. Some scientists are optimistic that a vaccine against the virus can be developed quickly, but a series of failed experiments have dashed their hopes.
It took many years of human efforts to control the epidemic of AIDS. Public health workers have tried a series of public health policies, such as controlling the use of needles and distributing condoms, and achieved corresponding results. Since then, the advent of anti-AIDS drugs has played a great role in the human struggle against the virus.
December 1, World AIDS Day
Today, millions of AIDS patients are receiving cocktail therapy, which uses a series of drugs to interfere with HIV infection of immune cells in order to prevent the virus from replicating with immune cells. In countries with strong economic strength, such as the United States, these drugs have indeed enabled many patients to regain relatively healthy bodies. Government organizations and some non-governmental organizations have sent these drugs to poorer countries, and AIDS victims in these areas have been able to prolong their lives. In 2005, the death rate of AIDS reached the highest in history, and 2.5 million people lost their lives that year, but the power of the virus has been weakened year by year since then. By 2013, the number of people who died of AIDS had dropped to 1.5 million.
Theoretically, we can make this number zero. Aids vaccine is still the best hope to achieve this goal, and recent research has rekindled people’s hope that an effective vaccine may be just around the corner. The widespread use of anti-HIV drugs can also effectively control the number of viruses in infected AIDS patients. At the same time, researchers are actively exploring, hoping to find the fatal weakness of these viruses.
Now human beings have a very deep understanding of HIV, and we even know the molecular changes that the virus has made to adapt to human beings in the past 100 years. It is entirely possible for us to destroy these adaptive traits one by one on this basis. In other words, the future of AIDS prevention and treatment, the answer may be hidden in its past.
02
West Nile virus
In the summer of 1999, some crows died strangely in the Bronx Zoo Park in new york, USA. Then, three flamingos in the zoo died suddenly, followed by a pheasant, a vulture and a cormorant.
At the same time, doctors in Queens, new york discovered a number of cases of encephalitis, the number of which is worrying. Usually, there are only 9 cases of this disease in the whole city of new york a year, but in August 1999, there were 8 cases in Queens just over a weekend. As summer passed, more cases appeared. Some patients were paralyzed by severe fever. By the beginning of September, 9 deaths had been reported.
On the one hand, doctors in Queens, new york are still worried about the strange diseases that broke out in the crowd. On the other hand, Tracy McNamara, chief pathologist of Bronx Zoo, got the answer to the question first. She suspects that it may be the same pathogen that causes the bizarre death of people and birds. Under her persuasion, the Centers for Disease Control and Prevention (CDC) began to analyze the genetic material of the virus. On September 22nd, researchers were surprised to find that birds didn’t die of St Louis encephalitis, but the real culprit was a pathogen called West Nile virus. This virus not only infects birds, but also affects people in parts of Asia, Europe and Africa.
At the same time, public health workers are still deeply puzzled by the inexplicable cases of human encephalitis and decide to search deeply. Two research teams have successfully isolated the genetic material from the virus that infects humans, and confirmed the type of virus-the West Nile virus that infects zoo birds actually killed people. This result also surprised researchers. In North and South America, no one has ever been infected with this virus.
Yellow virus, West Nile virus is one of them.
The United States is the birthplace of many kinds of human pathogenic viruses, some of which are ancient and some are new types of viruses. About 15 thousand years ago, human footprints reached the western hemisphere, and they brought a lot of viruses with them. When Europeans came to the New World, they brought a second wave of viruses. New diseases, including influenza and smallpox, swept across the American continent, killing millions of Native Americans. Since then, more new viruses have poured in. In the 1970s, HIV was introduced into the United States, and at the end of the 20th century, West Nile virus became a new "immigrant" in the United States.
It is only 60 years since the West Nile virus was first discovered by humans. In 1937, a woman in the West Nile region of Uganda began to have a strange fever. She came to the hospital, and the doctor isolated a new virus from her blood and named it after the discovery area. In the following decades, scientists found the same virus in many patients along the eastern Mediterranean coast, Asia and Australia. However, they also found that this West Nile virus does not mainly rely on human survival, but infects many kinds of birds and uses them to multiply and multiply.
At first, people didn’t know how the West Nile virus spread between people, birds and birds, or birds and people. It was not until scientists found the virus in a completely different species that the truth came out. This mysterious creature is the mosquito, which almost gives the virus a "wing"-when a mosquito carrying the virus bites a bird and sucks blood, it will inject its saliva into the wound of the bird’s skin, and at the same time inject the West Nile virus, which will multiply rapidly in the bird in a short time.
Studies on the genes of West Nile virus show that it originally evolved from Africa. Birds migrate from Africa to other parts of the Eastern Hemisphere, spreading the virus to new bird species and infecting humans. From birds to mosquitoes to birds, West Nile virus spread throughout the United States in just four years. At the same time, the virus also "landed" on millions of people, and only about 25% of those infected will have fever symptoms. Scientists estimate that from 1999 to 2013, more than 780,000 people were infected with West Nile virus, of which 16,196 developed encephalitis and 1,549 died.
After the West Nile virus arrived in the United States, it entered a stable life cycle, and the rhythm of this cycle was controlled by the life history of birds and mosquitoes. When chicks are born in spring, mosquitoes carrying viruses bite them. As a result, the number of birds infected with the virus continued to rise throughout the summer; New mosquitoes infect the virus by sucking the blood of these birds, and then bite people; People often spend more time outdoors in these relatively warm months of the year, and are more vulnerable to mosquito bites, thus being infected with West Nile virus.
Now that the West Nile virus has been integrated into the ecological environment of the United States, it may be difficult to kill them all. Even if doctors can develop vaccines to prevent humans from becoming the host of viruses, they can still thrive with the help of birds. Unfortunately, no West Nile virus vaccine has been approved at present, and probably never will be. Because although the virus infects many people, only a small part of them will develop encephalitis, and even fewer people will die from encephalitis. The cost of widely vaccinating Americans is extremely expensive, far exceeding the cost of treating those infected.
After arriving in America, the development prospect of West Nile virus is "optimistic". This is a warm and humid continent, and when the rainfall is heavy, the humidity and temperature are high, the epidemic situation is more likely to break out. Warm, rainy and sultry weather makes mosquitoes breed faster and lengthen their breeding season. At the same time, this weather can also accelerate the growth of viruses in mosquitoes. It seems that the West Nile virus has settled in this new continent, and our "efforts" are also making this home more comfortable.
03
Ebola virus
On December 2, 2013, a 2-year-old boy fell ill in the village of Meriando in southeastern Guinea. The child, Emil Wamuno, first had a fever, and then he began to vomit violently, accompanied by jet diarrhea and blood in his stool. No one in Meriando has seen similar symptoms. His family tried their best to take care of him, but by December 6, the child was still dead. It was a virus that killed the boy. When he died, the descendants of the virus had spread to other family members. Soon, Emil’s 4-year-old sister developed the same symptoms and died. Then the boy’s mother and grandmother. They probably got infected through the cruelest way we can think of-taking care of the dying boy.
If the virus stops here, this family tragedy is likely to be unknown outside the village of Meriando. Many people in Guinea die from viruses and other pathogens every day, but this virus is completely different. It is extremely deadly, and 70% of infected people will eventually die. The boy’s family has transmitted the virus to a nurse and the village midwife. After they got sick, the midwife was taken back to her hometown, and the virus continued to spread further by taking care of her family. At the same time, some people came from other villages to attend the funeral of Emil’s grandmother, and when they returned to their respective villages, they also fell ill.
Soon, the epidemic began to spread around the world. Meriando village is located on the border of Guinea, Sierra Leone and Liberia, and people often cross the border to do business or visit their families. The virus broke out in Sierra Leone and Liberia in a short time. However, because the disease is still concentrated in remote villages located in the tropical rain forest, the outside world is too lightly. It was not until March 2014 that the Guinean medical department finally announced that they had confirmed the culprit of the epidemic: Ebola virus.
Ebola virus under microscope
Some viruses are the old enemies of mankind. Rhinovirus began to make ancient Egyptians catch cold thousands of years ago, and endogenous retrovirus invaded the genome of our primate ancestors as early as tens of millions of years ago. There are also young people, and HIV only became a virus that can infect humans about 100 years ago. A large number of viruses have just begun to spread from person to person, triggering waves of new epidemics and arousing human concerns about new global epidemics. But of all these newly discovered viruses, none is more frightening than Ebola.
In 1976, Ebola virus entered the historical stage, and its first appearance showed its terrible lethality. In a remote area in Zaire (now the Democratic Republic of Congo), people began to have fever and vomit, and some patients were bleeding from all the openings such as nose and mouth, even from their eyes. A doctor collected a blood sample from a dying nun and put it in a thermos. Later, he sent the sample to Kinshasa, the capital of Zaire, and took it all the way back to Belgium by plane and gave it to the young virologist Peter Piot. Through the electron microscope, Pio observed a large group of snake-shaped viruses.
On high alert, scientists rushed to Zaire and finally arrived in Yambuku village to investigate the initial outbreak of the epidemic. There is a hotel here. Some nuns and priests are hiding in it. Visitors are blocked by ropes at the door. There is also a sign hanging on the rope, which reads: "Do not enter, entering may lead to death."
Soon, the Pio team found out how the unnamed virus spread. It turned out that the virus would spread from person to person. There is no evidence that this virus can float in the air like influenza or measles virus. In fact, it is spread by the body fluids of the victims. A local hospital used syringes repeatedly, and as a result, the virus spread to many patients. The staff who take care of the patients and wash the bodies of the dead are also sick.
Although Ebola virus is extremely deadly, its spread is relatively easy to cut off. Pio and his colleagues closed the hospital and isolated people with symptoms. After three months, the epidemic was controlled. 318 people died in this plague.
In the same year, Ebola virus appeared in Sudan, killing 284 people. Three years later, it made a comeback in Sudan, killing 34 people. Then it disappeared for 15 years, and in 1994 it launched an attack in Gabon, killing 52 people. Every outbreak has made Pio’s successors know more about Ebola virus. People gradually realize that as long as the patient’s whereabouts are tracked and properly isolated, new infections can be prevented. But they haven’t found a suitable vaccine, and they haven’t developed corresponding antiviral drugs.
Many viruses can suddenly break out when the conditions are right. But a virus like measles or chickenpox, once it breaks out, will not completely disappear from our bodies. It just hides in a low profile and spreads tepidly. The Ebola virus is different. When a plague subsides, it seems that the Ebola virus will disappear, but it will suddenly appear a few years later and launch a crazy attack again.
Some virologists are curious, where did the Ebola virus disappear in these years? Scientists have found that gorillas and chimpanzees are also infected with Ebola virus, and the mortality rate is very high, while bats have antibodies to Ebola virus, which seems to help bats coexist peacefully with the virus. Perhaps, under normal circumstances, Ebola virus will spread among bat individuals, but it will not cause any harm to them. Sometimes the virus will suddenly penetrate into human beings.
One thing is clear about Ebola virus: although we are completely unfamiliar with them, they are really an ancient virus. For millions of years, Ebola virus has been spreading in various mammalian hosts. They are harmless in some species, but sometimes they jump to other species and show a fatal side in these species. Humans are the latest target of Ebola virus attack. Meat or fruit contaminated by bat saliva may carry the virus, and people may be infected if they eat these contaminated foods. No matter by what route, once Ebola virus enters our body, it can quickly invade immune cells, leading to a serious inflammatory reaction. Patients will have violent diarrhea, vomiting, and sometimes massive bleeding until they die.
After Ebola virus enters a person’s body from an animal, its fate depends on the behavior of people around the victim. If people come into contact with infected people, they will be infected with Ebola and continue to spread to more people. In the first 37 years of human history, Ebola virus always disappeared by itself within a few months after a new outbreak, with the death or recovery of the host.
But in these 37 years, the living environment of human beings has changed. In the past, the sphere of influence of Ebola virus was generally confined to several neighboring villages, and it was difficult to spread to a larger scope. But now, more and more roads are cutting the rain forest, making people move to more towns, so that Ebola virus can find more hosts. However, in countries such as Guinea, Liberia and Sierra Leone, the development of public health is far behind the rapid urbanization. Years of civil war and extreme poverty have left few hospitals and doctors in these countries. When Ebola patients are taken to the hospital, medical staff will be infected and die first. The expertise needed to fight the epidemic in these countries is even more scarce.
No one knows how Emil, a 2-year-old boy, contracted Ebola, but the virus that spread from him to his family continued to make waves on a larger scale, triggering the largest Ebola epidemic in history. More people died in this plague than all those who died in the previous Ebola outbreak.
The virus then spread to Conakry, Freetown and Monrovia, the capitals of Guinea, Sierra Leone and Liberia. After a few months, there were no more Ebola patients in the hospital, and the patients were turned away or sent home to die. International health agencies are busy dealing with other epidemics such as influenza and polio, underestimating the extent of Ebola epidemic, and failing to provide help to West Africa that may slow down the epidemic. The governments of West African countries tried to isolate the affected cities and rural areas from their surroundings, but it didn’t play much role. The death toll soared, first 1000, then 2000, and then the number continued to increase.
Outside Africa, people know very little about Ebola, and their information mainly comes from literary works, such as the book Blood Epidemic: The Story of Ebola, which records a terrible virus attack, and movies such as Extreme Panic also make up many plots about the virus. Fear swept across the United States. A poll conducted in October 2014 showed that two-thirds of Americans were worried that the Ebola epidemic would spread to the United States, and 43% were worried that they were personally at risk of contracting Ebola. Rumors even say that Ebola virus can spread in the air. On October 23rd, it was reported that a doctor from new york who treated Ebola patients in Guinea returned to the United States and tested positive for Ebola virus. Before he developed symptoms, he had been to a bowling alley. Worried readers asked The New York Times if bowling could spread the virus. Reporter Donald McNeil Jr. quickly responded: "If someone leaves blood, vomit or feces on the bowling ball, the next person who touches the bowling ball will not even find these, and then touch his eyes, nose or mouth with his hand, which may be contagious." This is actually a euphemism, bowling can’t spread the virus.
Stills of Extreme Panic
Despite the public’s panic, the Ebola virus did not break out on a large scale in the United States. There are no other places. Nigeria used the public health measures used by Pio and others in other epidemics. As a result, the virus only caused 20 infections and 8 deaths before it died down. Senegal recorded a case without any death. Mali has also successfully controlled its epidemic. The reason why these countries have the upper hand in the confrontation with Ebola is that they have all been warned. On the contrary, the epidemics in Liberia, Guinea and Sierra Leone had spread silently before the outbreak, so they continued to be hit by the virus for a long time. In these three countries, the epidemic has expanded to an extent that cannot be easily controlled.
Epidemiologists watched anxiously as the number of infections soared, and they tried to predict how far the epidemic might develop. In September 2014, the Center for Disease Control and Prevention warned that there would be as many as 1.4 million Ebola cases by January 2015 without additional intervention.
Fortunately, some countries, including the United States, China and Cuba, began to send doctors and materials to African countries, and hospitals specifically for Ebola were built one after another. Public health workers also encourage people to bury Ebola patients in a safer way, so as to avoid being infected and dying themselves. Although the defense operation was carried out late and the measures were mild, by the end of November 2014, there was finally a turning point: the number of new cases in Liberia and Guinea began to decline. The following year, the epidemic quickly eased.
Although the Ebola epidemic has temporarily ended, it will not disappear forever. In September, 2014, ecologists and epidemiologists from Oxford University jointly published a research result, and made a detailed prediction on the location of Ebola outbreak in the future. They considered many kinds of animals that can carry the virus, as well as human settlements that overlap with the activities of these animals (such settlements are increasing). In their prediction, a total of 22 million people live in the Ebola risk zone. Although the probability that some of these 22 million people are actually infected with Ebola virus by animals is very low, once infected, the danger will be enormous.
04
SARS, MERS virus
Since the first discovery of Ebola virus, other viruses have also appeared. They have emerged from completely different places, which may be thousands of miles away from each other.
For example, in November 2002, a farmer from China came to the hospital with a high fever and died soon. Then, people in the same area appeared the same disease one after another, but at this time, the epidemic did not get worldwide attention until the disease infected an American. This man went to China to do business. On the plane flying back to Singapore from China, he suddenly started to have a fever. The plane stopped in Hanoi, and the businessman never left there alive. Although most cases are still concentrated in mainland China and Hongkong, people all over the world are getting sick. The death rate of this disease is as high as 10%, and it usually takes only a few days to kill people. This epidemic is brand-new in medical history, and it needs a new name. Doctors call it severe acute respiratory syndrome or SARS.
Structural diagram of SARS coronavirus
Based on the accumulated experience of HIV and Ebola virus, scientists suspect that SARS virus evolved from viruses that originally infected other animals. So they set out to analyze the viruses in animals that Chinese often came into contact with. Whenever a new virus was discovered, they added corresponding branches to the evolutionary tree of SARS. After a few months, scientists finally reconstructed the history of SARS.
The virus may have originated from bats in China, and one of them spread to civet cats, a mammal that looks like cats. Civet cats are common in the animal market in China. Humans may have become hosts in the process of buying and selling civets. It turns out that the biological characteristics of this virus just make them suitable for human-to-human transmission, and unlike Ebola virus, SARS virus can attach to tiny aerosol particles and spread in the air.
Although the SARS epidemic has spread beyond Asia, fortunately, public health measures to prevent the early epidemic of Ebola have also successfully subdued SARS. This epidemic has ravaged more than 8,000 people worldwide and killed more than 700 people. In comparison, the flu kills about 250,000 people every year-it can be said that we have successfully escaped a bullet fired by SARS at humans.
Ten years later, another coronavirus appeared in Saudi Arabia. In 2012, doctors in Saudi Arabia noticed that some patients suffered from respiratory diseases with unknown causes, and nearly one third of them died of illness. This disease is called MERS, which is short for "Middle East Respiratory Syndrome". Virologists isolated pathogenic viruses from patients and studied the genes of MERS virus. They used these genes to look for similar fragments in other species, and soon people’s eyes were fixed on bats in Africa.
However, how African bats became the fuse of the Middle East respiratory syndrome epidemic is still incredible. It was not until scientists studied the camel, a mammal on which people in the Middle East depend, that important new clues began to appear. They found that camels generally carry MERS virus. The virus is continuously released through camel nose secretions. A reasonable explanation for the origin of MERS is that bats may transmit the virus to camels in North Africa. Camel trade from North Africa to the Middle East is frequent, and a sick camel may have brought the virus to its new home.
Scientists have reconstructed the transmission history of MERS, and have every reason to worry that once MERS breaks out, the epidemic may be even more terrible than SARS. Every year, more than 2 million Muslims go to Saudi Arabia for the annual pilgrimage to mecca. It is not difficult to imagine that MERS virus will spread rapidly among dense people and then go to their homes around the world with pilgrims. Fortunately, so far, scientists’ fears have not come true. As of February 2015, 1,026 people were diagnosed with MERS, of which 376 died. Almost all cases occurred in Saudi Arabia, especially in hospitals. Perhaps MERS is best at attacking people whose immune system is weakened by illness. Unless MERS undergoes drastic evolution again, it may always be a dangerous but rare threat within hospitals in the Middle East.
If the epidemic doesn’t always come so unexpectedly (if we can make early warning of these emergencies), we can be better prepared and not caught off guard. However, the next time a virus is transferred from wild animals to human bodies, it is likely to trigger a large-scale epidemic, and we may know nothing about the pathogenic virus.
In order to make up for these cognitive loopholes, scientists are conducting more animal research to find the genetic material of the virus from their bodies. But we live on a veritable "virus planet", and the workload of scientists is huge. Among the new viruses they continue to discover, we don’t know which ones will cause plague, and it is even possible that these viruses will not pose a threat to human society. But that doesn’t mean we can just ignore them. On the contrary, we just need to be vigilant, so that we can take measures to stop them before they have a chance to enter our species.
This article is excerpted from
Virus planet
By Carl Zimmer
Translator: Liu Yang
Press: Guangxi Normal University Press
Publication date: April, 2019
Editor Barbarossa
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Original title: Popular Science: Five Viruses Carried by Animals and Global Disasters Caused by Them
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