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Viruses are unseen but dynamic players in the ecology of Earth. They move DNA between species, provide new genetic material for evolution, and regulate vast populations of organisms. Every species, from tiny microbes to large mammals, is influenced by the actions of viruses. Viruses extend their impact beyond species to affect climate, soil, the oceans, and fresh water. When you consider how every animal, plant, and microbe has been shaped through the course of evolution, one has to consider the influential role played by the tiny and powerful viruses that share this planet.
Before Willner’s expedition, scientists had assumed the lungs of healthy people were sterile. Yet Willner discovered that, on average, people have 174 species of viruses in the lungs. Only 10 percent of the species Willner found bore any close kinship to any virus ever found before. The other 90 percent were as strange as anything lurking in the Cave of Crystals.
The very word virus began as a contradiction. We inherited the word from the Roman Empire, where it meant, at once, the venom of a snake or the semen of a man. Creation and destruction in one word.
Eventually, they learned how to cultivate some viruses outside of living animals and plants, using nothing more than colonies of cells growing in dishes or flasks.
But Stanley had also made a small but profound mistake. The British scientists Norman Pirie and Fred Bawden discovered in 1936 that viruses were not pure protein, but only 95 percent. The other 5 percent consisted of another molecule, a mysterious strand-shaped substance called nucleic acid. Nucleic acids, scientists would later discover, are the stuff of genes, the instructions for building proteins and other molecules. Our cells store their genes in double-stranded nucleic acids, known as deoxyribonucleic acid, or DNA for short. Many viruses have DNA-based genes as well. Other viruses, such
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In the decades that followed, virologists went on to dissect viruses, to map their molecular geography. While viruses contain nucleic acids and proteins like our own cells, scientists found that differences between the structures of viruses and cells are many. A human cell is stuffed with millions of different molecules that it uses to sense its surroundings, crawl around, take in food, grow, and decide whether to divide in two or kill itself for the good of its fellow
They typically were just protein shells holding a few genes. Virologists discovered that viruses can replicate themselves, despite their paltry genetic instructions, by hijacking other forms of life. They inject their genes and proteins into a host cell, which they manipulate into producing new copies of themselves. One virus goes into a cell, and within a day a thousand viruses may come out.
It’s been estimated that every human being will spend a year of his or her life lying in bed, sick with colds. The human rhinovirus is, in other words, one of the most successful viruses of all.
They trigger the cells to open up a trapdoor through which they slip. Over the next few hours, a rhinovirus will use its host cells to make copies of its genetic material and protein shells to hold them. The host cell then rips apart, and the new virus escapes.
In order to recover from a cold, we have to wait not only for the immune system to wipe out the virus, but also for the immune system itself to calm down.
But the transition from bird to human is not a simple one. The genes a bird flu virus needs to thrive are different from those needed inside a human body. Human bodies are cooler than bird bodies, for example, and that difference means that molecules need different shapes to run efficiently.
When a flu virus hitches a ride aboard a droplet and infects a new host, it sometimes invades a cell that’s already harboring another flu virus. And when two different flu viruses reproduce inside the same cell, things can get messy. The genes of a flu virus are stored on eight separate segments, and when a host cell starts manufacturing the segments from two different viruses at once, they sometimes get mixed together. The new offspring end up carrying genetic material from both viruses. This mixing, known as reassortment, is a viral version of sex. When humans have children, the parents’
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By sequencing its genes, scientists have traced the virus’s origins to four separate strains. The oldest of these strains has been infecting pigs since the 1918 pandemic (it’s possible the pigs got it from us). A second strain emerged in the 1970s, when a bird flu infected pigs in either Europe or Asia. And a third strain jumped later from birds to pigs in the United States. By the late 1990s, all three strains had combined into a new form, called a “triple reassortant” by scientists. Unnoticed at the time, it silently moved from pig to pig in large closed barns. The triple reassortant then
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Instead of speeding up cell division, they issue commands to their host cell to make many new viruses. When the cell reaches the surface, it bursts open with a big supply of HPV that can seek out new hosts to infect.
The scientists followed the children for 109 days. Among the children who took the sugar pill, 6.7 out of every
1,000 got dysentery. Among the children who took the phage pill, that figure dropped to 1.8 per 1,000. In
other words, taking phages caused a 3.8-fold decrease in a child’s ch...
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Marine phages influence the ecology of the world’s oceans. They leave their mark on Earth’s global climate. And they have been playing a crucial part in the evolution of life for billions of years. They are, in other words, biology’s living matrix.
That’s because microbes themselves are the planet’s great geoengineers. Algae and photosynthetic bacteria churn out about half of the oxygen we breathe. Algae also release a gas called dimethyl sulfide that rises into the air and seeds clouds. The clouds reflect incoming sunlight back out into space, cooling the planet. Microbes also absorb and release vast amounts of carbon dioxide, which traps heat in the atmosphere. Some microbes release carbon dioxide into the atmosphere as waste, warming the planet. Algae and photosynthetic bacteria, on the other hand, suck carbon dioxide in as they grow,
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The gorilla SIV, they found, had originated from chimpanzees. To better understand how gorilla SIV was related to viruses in chimpanzees and humans, Peeters and her colleagues set out to systematically gather gorilla stool from across their range as well. Searching through more than 3,000 samples of gorilla feces, they failed to find any gorilla SIV outside of Cameroon. But inside Cameroon, the story was different. They found more gorilla SIV. In 2015, Peeters and her colleagues announced that two of these new lineages of gorilla SIV were the ancestors of HIV-1 O and P,
Using this method, scientists have found that both HIV-1 Group M and HIV-1 Group O originated in the early 1900s. (There isn’t enough data to estimate the dates for the other lineages of HIV.)
In 2005, the annual death rate from HIV peaked at 2.5 million people a year. Since then, it’s slowly declined. By 2013, it was down to 1.5 million people.
Vector-borne viruses like West Nile virus require a special versatility to complete their life cycle. Mosquitoes and birds are profoundly different kinds of hosts, with different body temperatures, different immune systems, and different anatomies. West Nile virus has to be able to thrive in both environments to complete its life cycle. Vector-borne viruses also pose special challenges to doctors and public health workers who want to stop their spread. They don’t require people to be in close contact to spread from host to host. Mosquitoes, in effect, give the viruses wings.
On its own, a single infected bird could not have triggered a nationwide epidemic. The viruses needed a new vector to spread. It just so happens that West Nile viruses can survive inside 62 species of mosquitoes that live in the United States. The birds of America turned out to be good hosts as well. All told, 150 American bird species have been found to carry West Nile virus. A few species, such as robins, blue jays, and house finches, turned out to be particularly good incubators.
That’s because the virus infects a huge number people but only causes a relatively modest cases of encephalitis, and even fewer deaths. Vaccinating a large portion of the United States population would be tremendously expensive, far greater than the cost of hospitalizing the people who get sick from the virus.
They found that epidemics tended to occur when there was heavy rainfall, high humidity, and warm temperatures. Warm, rainy, muggy weather makes mosquitoes reproduce faster and makes their breeding season longer. It also speeds up the growth of the viruses inside the mosquitoes. Now that West Nile virus has made a new home here, we’re making that home more comfortable.
Some viruses are old enemies of our species. Rhinoviruses gave ancient Egyptians colds, and endogenous retroviruses invaded the genomes of our primate ancestors tens of millions of years ago. Other viruses are younger. HIV, for example, became a human virus about a century ago. And other viruses are only just starting to patter down on our species, triggering outbreaks and raising fears of new global plagues. Of all these newly discovered viruses, none inspires more fear for the future than Ebola.
They also found antibodies to Ebola in bats, which seemed to tolerate the virus. It’s possible that Ebola normally circulates harmlessly from bat to bat, spilling over into humans from time to time.
We humans have become Ebola’s latest spillover host. It’s possible that people pick up Ebola virus when they eat infected meat, or perhaps fruit that’s been contaminated by bat saliva. However Ebola gets into our bodies, it promptly invades our immune cells and quickly causes massive amounts of inflammation. The virus makes people fatally leaky. They release huge quantities of diarrhea, vomit, and sometimes blood.
The virus likely started in Chinese bats. A lineage of the viruses then began to spill over into a catlike mammal called a civet. Civets are a common sight in Chinese animal markets, and it’s likely that humans became spillover hosts as well. The virus turned out to have the right biology for spreading from people to people—and unlike Ebola, it could spread on fine aerosol droplets.
How African bats could have caused a Middle Eastern epidemic was a question without an obvious answer. But an important new clue emerged when scientists examined the mammals that many people in the Middle East depend on for their survival: camels. They began to find camels rife with MERS viruses, which oozed from their noses in drops of mucous. One possible explanation for the origin of MERS is that bats passed on the virus to camels in North Africa. There’s a healthy trade in camels from North Africa to the Middle East. A sick camel may have carried the virus to its new home.
But other scientists urged holding onto smallpox stocks. They pointed out that the eradication campaign might not, in fact, have been a complete success. In the 1990s, Soviet defectors revealed that their government had set up labs to produce a weaponized form of smallpox, one that could be loaded in missiles and launched at enemy targets. After the fall of the Soviet Union, those biological warfare labs were abandoned. No one knows what ultimately happened to the smallpox viruses used for that research. We are left with the terrifying possibility that ex-Soviet virologists sold smallpox
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The mimivirus turned out to have virus genes—and a lot of them. Before the discovery of mimiviruses, scientists had become accustomed to finding only a few genes in a virus. But mimiviruses have 1,018 genes. It was as if someone took the genomes of the flu, the cold, smallpox, and a hundred other viruses, and stuffed them all inside one protein shell. The mimivirus even had more genes than some species of bacteria. In both its size and its genes, mimivirus had broken cardinal rules for being a virus.
In 2014, French researchers thawed out pieces of Siberian permafrost that had been frozen for 30,000 years. They discovered giant viruses in the thawed soil—at 1.5 micrometers long, they’re the biggest giant viruses yet found.
At long last, we may be returning to the original two-sided sense of the word virus, which originally signified either a life-giving substance or a deadly venom. Viruses are indeed exquisitely deadly, but they have provided the world with some of its most important innovations. Creation and destruction join together once more.
