The emergence of pathogens

When I was a medical student, I had a summer internship helping a doctor who conducted medical examinations of workers from the West Virginia labor corps. It was a great experience – a lot of clinical work. I have learned to examine healthy young people carefully. My teacher, Dr. Fred Cooley, was practical, smart and funny. Work with him ended about an hour of the day, so then I went to the hospital and worked with others, taking a variety of patients. Students here was not very many, so that me, Intern with pile issues,??? with open arms.

One day we were called to see an 11-year-old boy who was hospitalized with acute pain. He lived in a small, very conservative Baptist town, was perfectly healthy, but two days ago he complained of indigestion and fever. The next day she got taller and added a headache. On the third day around the body emerged a small purple rash. His parents were scared and took him to the hospital – it was the right decision. Doctors from the emergency room quickly diagnosed spotty fever of the Rocky mountains, a disease caused by a tick bite infected with a bacterium called “Rickettsia”. For the first time this disease was discovered in the valley Bitterroot in Montana (hence the name), but more often it occurs in the Eastern part of the country.

The microbe multiplies in the cells lining the blood vessels, causing a strong immune response. This explains the rash, because the vessels are inflamed and burst, and headache: in the vessels of the brain is the same process. It begins a kind of encephalitis. The boy was given tetracycline, an antibiotic that saved many lives. If the treatment does not start immediately, then in 30% of cases, spotted fever is fatal.

I examined him with the doctors. The chamber was dark, because the light hurt the boy’s eyes – a sign of brain damage. The body was covered with purple dots – a number I have not seen since anyone. Some were joined in long blackish-purple lines. Hair’s tangled. He was sweating and throwing himself from side to side; his hands were tied to the bed to avoid hurting himself or others. He was shouting something incoherent down his throat, obviously hallucinating. Sometimes it was possible to make out separate words, but they were curses. There was no end in sight. The parents hid in the corner of the chamber where he learned all these words? We knew that his lack of restraint caused by the encephalitis.

Fortunately, thanks to the treatment, the boy gradually recovered, and five days later he was discharged from the hospital – he was treated at home. He did not remember anything, but I am sure that his parents have not forgotten not only a terrible sight, but also a wonderful healing.

Pathogens like Rickettsia are bacteria that cause disease. They are accompanied by fever, chills, pain and aches, which are bedridden for a few days or even more. They can kill you, slow or fast. It happens alone or in the company of thousands of others. We usually call them “harmful microbes” and since they were discovered 150 years ago, we have been doing everything possible to destroy them. For the past 70 years, we have been waging an aggressive war against pathogenic bacteria with multiple antibiotics, saving millions of lives around the world. But, to our disappointment, this battle seems endless. Microorganisms mutate faster than lightning and develop resistance to some of the most effective antibiotics. And, even more frustrating, the struggle has led to serious unintended consequences for our health and well-being.

But before we consider the consequences, let’s first find out what we’re dealing with. All pathogens have one thing in common-they are harmful to us. But differ from each other markedly. For example, biological nature: is it bacteria or viruses? Do they produce a toxin that wounds our cells while living somewhere in the middle of the gastrointestinal tract, like battleships bombarding the shores with cannons? Or, like the Marines themselves landed on the “beach” and go on the attack?

It would be tempting to think of pathogens as evil in nature, but they are not. Like the wolves in Yellowstone, they’re just predators. Quite often, fighting for their own survival, pathogens cause terrible harm to carriers. Sometimes by accident-just the consequences of activities. But for pathogens that are well adapted to their carrier, the harm done is beneficial. For example, bacteria that cause tuberculosis cause people to cough, spreading the infection through the air and helping them spread. The rabies virus attacks the area of the brain responsible for aggressive attempts to bite, and spreads through the saliva of infected animals.

David Quammen in his book Spillover, which is devoted to infectious diseases, notes: predators for us are large animals that eat prey from the outside; but pathogens are small, which destroy it from the inside {45}. Very appropriate comparison.

Eskimos say that “wolves make caribou healthier“. A healthy deer-caribou can easily drive away the wolf, but the weaker member of the herd, they easily break and thereby thin out the herd. Same with pathogens. Seven billion people now live in the world, often in poverty-stricken conditions. Hungry, weak, poor, often without access to modern medicines, people can become easy prey. I’m not saying thinning out humanity is a good thing. But this has already happened and is likely to happen always.

There are pathogens that just get under your skin through cuts and scratches. If the wound is not thoroughly washed, you can get an infection, but it is curable: weak – washing, plaster and kiss, stronger – deep cleaning. Sometimes you need antibiotics. But such diseases are purely accidental. In addition, pathogens are almost never transmitted to another person.

Organisms that do not usually cause diseases can develop amazing virulence and kill even the strongest and healthiest people very quickly. Many in the intestine is found E. coli; most of its strains are harmless. But in 2011 in Germany there was an epidemic of E. coli, when people ate infected Brussels sprouts. At least two strains exchanged genetic material, and the result was an incredibly virulent organism that managed to infect more than four thousand people. About eight hundred damaged kidneys, and some-irreversibly, and fifty people were lost.

Contagious diseases are caused by microorganisms that colonize your body, multiply uncontrollably and worsen the condition. These can be influenza viruses, bacteria that cause whooping cough, fungi growing on the mucous membranes of the mouth, a variety of free-living single-celled organisms that are called protists-for example, a rather evil amoeba that causes dysentery and bloody diarrhea. More than 14,000 human pathogens are now classified. They are of high and low degree of danger. For example, Rickettsia, which caused spotty fever in a healthy little boy, is a high risk. But organisms, acting only on people with chronic lung diseases, can be a low risk-it means they are less virulent and cause disease only when the person is already weakened, so it is unlikely to affect healthy.

All infectious disease-causing microorganisms have come to us from our Primate relatives, from domestic animals, as well as from other, more and more dangerous ways-for example, from wild animals. Some have “jumped” on humans so long ago that we can no longer establish their origin. But the other track is quite real: the plague from fleas on rodents; rabies from bats; influenza from birds; the Lyme disease – also from rodents, by ticks. Some of the deadliest pathogens are stray viruses that have appeared relatively recently: Ebola, SARS, hunt’s virus, Marburg virus, swine and avian influenza. They are almost impossible to eradicate, because we humans are in contact with the animals in which they are found. When mosquitoes, for example, are involved in disease transmission, as in malaria, the picture becomes even more complex.

Some particularly successful human pathogens no longer need their original animal reservoirs. At some point in time, smallpox, polio and measles viruses have evolved and become specialized in humans; they only affect us (and thus are vulnerable to complete destruction – for example, the human smallpox virus). But the “800-pound gorilla” among the new pathogens, HIV, which has moved to people with chimpanzees, is now transmitted from person to person through sexual acts or infected blood. It all started with a few random infections, and now-more than 100 million people.

I believe that we ourselves are creating favourable conditions for the spread of pandemic microbes: it is now easier than ever to travel around the world; we are facing new organisms, and our immunity has become weaker.

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Throughout most of human history, the pathogens that cause the world’s greatest epidemic diseases – smallpox, measles, influenza, plague, polio, cholera, typhoid, scarlet fever and diphtheria – have been harmless and have not killed us. The reason is related to the size of the population. When ancestors engaged in hunting and gathering in Central Africa, they lived in small groups, from thirty to sixty people, widely spread over a huge Savannah. And so it was almost 2 million years ago, until about 200,000 years ago, Homo sapiens appeared. Our existence within civilizations that emerged 80,000-10,000 years ago is just a point in a long history. It was in the prehistoric period that we became what we are now.

The ancestors were self-sufficient. Abundant times men brought in enough meat to feed the entire tribe; the women gathered fruits, nuts and herbs. But when food was scarce, they suffer. Hunters brought themselves to exhaustion in pursuit of prey. Women stopped menstruating or lactating because of malnutrition. Worst of all with prolonged droughts – entire tribes died out without a trace. Hyenas and vultures ate them to the bone.

But from the modern point of view, such an unreliable existence had one undoubted advantage: there were no epidemics. Ancestors suffered from simple infections like worms-parasites and yaws – chronic, non-fatal diseases. But there were no serious, because small tribes lived in complete isolation, they had no neighbors who could bring harmful bacteria or viruses. If, by some unfortunate accident, someone with a contagious disease was beaten, there were not so many options: nothing happened; the entire tribe died out; some were sick, others were immune to it. After that, the pathogen somehow had nowhere to go, no one to infect. He was isolated and dying.

But already hunters and gatherers had to deal with latency. Many millennia ago, tuberculosis and several other known pathogens adopted a similar strategy. They infected one generation, then hid and infected the next, avoiding the question “what to do when the potential carriers run out“.

Another example is chicken pox. If you, like many children, once inhaled the varicella-zoster virus, you had a fever soon after, and then a rash all over your body. A few days later she came down, and two weeks later you are fully recovered. With rare exceptions, all children who have had chickenpox receive life-long immunity from the varicella-zoster virus. This seems to be all… but not quite. Virus is smart. It hides in nerve cells along the spine and in similar places in the head. And lives so for decades, silently, quietly, without causing any discomfort.

And then, usually when you’re over sixty, seventy, or eighty, you feel itchy under the rib. The next day, in his path stands a rash. Looking closely, you notice that this rash has the same vesicles as in childhood with chickenpox, but this time localized. And now you have shingles, or as the doctors say, herpes zoster.

So the older you are, the more likely you are to get shingles. For decades, the immune system does not allow the virus to do anything, but when it weakens with age, the disease is not suppressed and again takes up work-causes shingles. When the vesicles are opened, the virus enters the air and can infect a child who has not yet received immunity.

And the cycle repeats. In this way, the varicella-zoster virus sometimes does not touch several generations. In a small settlement for decades, the infection can live in secret and not manifest itself in an acute form. But the virus is able to “come to life” at any time and infect a new group of susceptible people. Well adapted to us, it has two mechanisms of distribution: through a child suffering from chickenpox, or through his elderly relative, who once in childhood had chickenpox, and now received shingles. Contagious, latent, contagious-this strategy has led to the most successful results over a long period.

The bacterium causing tuberculosis is transferred in the same way – directly after reactivation of the latent infection (usually-at elderly people). This helped it to survive in small isolated populations that dominated during the prehistoric period. But then, as humanity increased, the incidence of tuberculosis soared.

Now small populations are the exception. About ten thousand years ago, the invention of agriculture provided food security. The population began to rise sharply. Trade flourished. Villages grew into cities, overpopulation became the norm. It then blossomed epidemic disease.

Measles is the most famous example illustrating the work of so-called “crowd diseases”. Epidemics often go in waves, and is quickly spread from one to another, while not getting almost all. There are two possibilities: either recovery or death. In the case of this disease, the survivors develop antibodies, the immune system remains for life. The measles virus is the most contagious disease known to mankind; its contagiousness index exceeds 95%. For comparison, a new strain of influenza infects only a third to half of those who did not previously suffer from it.

When I was a student in Africa, I saw many children with measles. Most often they had high fever, sore throat, red eyes and frequent dry cough, and this is a very effective way of transmission. Any child who has not previously dealt with this virus immediately gets sick. After about a week of coughing and runny nose, there is a characteristic rash behind the ears, which then spreads throughout the body: the main symptom of measles. Now in developed countries vaccinated, but in Africa and other developing regions with this until progress has been slow. In 2011, 158,000 people died: 432 per day (mostly children), or 18 per hour.

To survive, the virus needs to find a new susceptible carrier every two weeks. Like a pyramid scheme, it requires a constant influx of victims. In fact, measles can only survive if 500,000 people live close enough to each other. Under these conditions, a three percent birth rate gives 15,000 susceptible children a year, guaranteeing annual measles epidemics. But the human population reached 500,000 about ten thousand years ago, after which the associated epidemics began. So maybe measles jumped from animal to human many times back in prehistoric times, but the population wasn’t enough to support it, and the disease was dying out.

On many Islands, such as the Faroes in the North Atlantic, measles could not occur for decades. But when in 1846 the ship was brought to the Islands of the sick, the virus quickly spread {51}. A similar epidemic occurred in Hawaii in the middle of the XVIII century-measles was brought there by a sailor. People suffering from high temperatures tried to cool off in the ocean. But it didn’t help: every fifth died. After the virus died, and again it was brought only many years later.

The emergence of cities has brought new dilemmas. Food had to be stored, and it attracted hungry pests and parasites. In the pits and in garbage piles appeared rodents. So began his life bubonic plague, which carry fleas in rats, and causes-the bacterium Yersinia pestis. The so-called” Black death ” began in Europe in 1347 and in ten years killed a quarter to a third of the population. After the first victims of the epidemic spread without the participation of rats-infected fleas jumped from one person to another, and patients with pulmonary plague coughed on others.

In 1993, it began in Kinshasa, the capital of Zaire. Years of war and corruption forced the government to print money. As a result, hyperinflation began. People bought that could because tomorrow everything could rise in price again. Many kept the grain, which attracted the rats.

The industrial revolution has led to a new surge in population, and many contagious diseases have become even more dangerous. In overpopulated cities, scarlet fever caused by Streptococcus, diphtheria, typhoid fever, and tuberculosis were rampant, the most common cause of death in the U.S. in 1900. Different types of diarrhoea caused by pollution of drinking water by sewage affected more and more susceptible people. And 20 % of children did not live to five years because of diarrhea, whooping cough, diphtheria, scarlet fever and other epidemic diseases.

The more cities grew, and the better transport and trade links, the more our indigenous micro – organisms – endemic or latent-were joined by epidemic pathogens that required large and dense populations to survive, the more they flourished. They were real troublemakers who killed and maimed many people, especially children. Even tuberculosis, which has existed for a long time, appeared strains selected for virulence and ease of transmission. Together, they thin out the human “pack”, and the price is very expensive. No family could not consider itself invulnerable-neither rich nor poor. They only prayed for deliverance from the disease. The situation began to improve only in the late XIX-early XX century, when seriously thinking about sanitation, and then began to invent vaccines. Thanks to the joint efforts of many countries, smallpox has completely disappeared from the face of the earth, the spread of polio has significantly decreased and measles is being restrained. Another incredible breakthrough in the fight against pathogens occurred when, fortunately, antibiotics were discovered.

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