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  • Viruses are tiny infectious agents that dominate much of the microscopic world.

  • They're incredibly abundant.

  • There are more viruses in a single drop of seawater than there are people living in New

  • York City.

  • And there are more viruses on Earth than there are stars in the universe.

  • They've had a lot of time to become so plentiful.

  • Viruses were here long before we were.

  • Some scientists believe they're older than any life on Earth.

  • They are also incredibly diverse.

  • Viruses can invade all types of life, from animals to plants, bacteria to fungi.

  • But what are they, exactly?

  • Viruses aren't technically alive--though that's still a matter of scientific debate;

  • they're merely packets of genetic information.

  • Some carry that code in single strands of RNA, others in double strands or in DNA.

  • But they all use those instructions as a blueprint for invading healthy cells, orhosts.”

  • They enter and take over a cell to replicate: either destroying the host cell's genetic

  • code or splicing themselves onto it.

  • After replicating, viruses escape to hijack other cells, often destroying their host cells

  • in a process calledlysis.”

  • This isn't always a bad thing.

  • By breaking and restructuring other cellslike ones inside phytoplankton in the oceanviruses

  • play an important role of increasing the efficiency of the Ocean's “biological pump”: the

  • process of sequestering carbon dioxide from the atmosphere to the ocean floor.

  • An ancient virus also gave rise to the human placenta, which is why our babies aren't

  • born from eggs.

  • But those were happy side effects.

  • Viruses only care about one thing: making more viruses.

  • And that often causes big problems.

  • Starting in the late 1800s, scientists discovered many diseases spread by unknown, unseen pathogens.These

  • mysterious infections were destroying tobacco plants and infecting livestock across Europe

  • and the United States.

  • In 1902, American physician Walter Reed discovered that a similar agent had been the cause of

  • the Yellow Fever epidemic.

  • Researchers began calling these pathogensviruses,” Latin for poison.

  • At the time, Reed and his peers could isolate viruses with cutting-edge filters because

  • they happened to be much smaller than bacteria.

  • But they couldn't actually see them with a regular microscope.

  • The tobacco mosaic virus would be the first to come into actual view with the invention

  • of the electron microscope in the 1930s.

  • Once we could see viruses, we started to realize that they were everywhere, including inside

  • our own bodies.

  • Viruses have replicated inside humans throughout our evolution.

  • That's why about eight percent of the human genome is derived from virusesremnants

  • of infections in our ancient ancestors.

  • These viruses are generally inactive, orlatent,” though some can be reactivated by autoimmune

  • diseases, neurodegenerative conditions, chronic inflammation, and cancer.

  • In addition to going latent, sometimes for decades, viruses can also mutate.

  • This can happen as a result of physical damage, chemical changes within the virus's genetic

  • material, or errors during the replication process.

  • Mutation is the reason that the novel coronavirus, SARS-CoV-2, was able to jump from infecting

  • bats to infecting humanssomething known ashost-switching.”

  • Coronaviruses in particular have a unique way of mutating: they readily swap bits of

  • RNA with other coronaviruses in a process calledrecombination.”

  • That makes it easy for the virus to adapt to new species.

  • The coronavirus pandemic has brought the adaptability of viruses into full view.

  • What remains somewhat hidden is how many more deadly viruses like it might be waiting to

  • jump from animals into humans.

  • Some estimates give reason for concern.

  • A 2018 study found that of 111 viral families identified worldwide, there are some 631,000

  • to 827,000 yet-unknown viruses thatlikely have the capacity to infect people.”

  • It's unclear how many of them could one day pose a threat to humans.

  • But what is clear is that we still have so much to learn about the multitudes of viruses

  • that share the world with us.

Viruses are tiny infectious agents that dominate much of the microscopic world.


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ウイルス サイエンティフィック アメリカ(Decoded: What are viruses, exactly?)

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    kuma に公開 2021 年 05 月 14 日