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  • Here at SciShow, we talk a lot about the fascinating, complicated, and often very weird stories

  • of discovery and collaboration that led to the science we know today.

  • But one of the strangest is something we haven't covered in much detail before, and it's a

  • biggie: the decades it took to figure out exactly what HIV and AIDS were, and how to

  • prevent and treat them.

  • Since the start of the AIDS crisis, some 70 million people have been infected with HIV,

  • and 35 million of those people have died.

  • Both those numbers are staggering in their own way, and together, they tell the story

  • of a disease that has led to an incredible amount of loss, but also one thatif youre

  • lucky enough to have access to the right medicinesis no longer a death sentence.

  • So, in honor of World AIDS Day on December 1, we want to tell you that story.

  • There’s a lot to cover, so well do it in two parts.

  • This episode, well go over how we figured out what HIV is, when the infection morphs

  • into AIDS, and where we think the virus came from.

  • Next time, well look back to the earliest treatments, the arrival of antiretroviral

  • drugs, which were complete game-changers, and go over the creative ways scientists are

  • now thinking about prevention and possibly even a cure.

  • But first, the basics.

  • HIV, or human immunodeficiency virus, is a retrovirus that infects immune cells, most

  • notably what are known as CD4 T cells.

  • Theretroviruspart just means that the virus uses RNADNA’s more wily,

  • less stable cousinas its genetic material, and that once HIV infects a cell, it makes

  • a DNA version of its genome with a special enzyme, then inserts that DNA into the host genome.

  • If that sounds sneakywell, it is.

  • And it’s part of why HIV has been so difficult to treat, which we'll talk about more next time.

  • Now, those CD4 T cells that HIV infects and ultimately kills are a kind of white blood

  • cell known ashelper’ T cells.

  • When they recognize a threat, they pump out proteins that help coordinate a bunch of different

  • immune responses.

  • You definitely want them around.

  • HIV is spread by bodily fluids, including blood, semen, vaginal fluid, and breast milk.

  • That’s why HIV can be transmitted through sex, dirty needles, breastfeeding, and any

  • other swapping of fluids you might dowith a major exception: saliva isn’t one of those fluids.

  • Saliva is full of other stuff that prevents HIV from being infectious, like antibodies

  • and a bunch of antimicrobial proteins.

  • So unless there’s a lot of blood in your saliva for some reason, it can't transmit HIV.

  • When someone is first infected, they might feel like they have a bout of the flu, with

  • a fever, headache, rash, sore throat, and muscle and joint pain.

  • That’s because the virus is infecting lots of cells and the immune system is trying to

  • fight it off.

  • But within a few weeks those symptoms pass because by then the person has specific antibodies

  • that can keep the virus from running totally rampant.

  • After that, they usually feel fine for a long timein many cases, a really long time,

  • like several decades.

  • Until, one day, they don’t, because the virus has finally killed off too many T cells,

  • leaving the body unable to properly defend itself against pathogensanything that

  • might be dangerous or infectious.

  • That’s when someone is said to have AIDS, or acquired immune deficiency syndrome.

  • Usually AIDS is diagnosed once the person’s T cell count falls below 200 cells per microliter

  • of blood, which is well below the normal 500-1500, or if they develop what's called an opportunistic infection.

  • These are infections that anyone with a reasonably strong immune system would be able to fight

  • off, easy-peasy.

  • But because HIV has obliterated most of their T cells, AIDS patients get sick.

  • And, they can die.

  • Most of the time it’s an opportunistic infection that killed them.

  • So, some of that was probably familiar to you, but pretend for a moment that youve

  • never heard of HIV or anything else I just mentioned.

  • Because back in the ‘80s, we didn’t know these basic facts.

  • All doctors knew was that suddenly, healthy young gay men were developing extremely rare

  • infections and cancersand, it was killing them.

  • One of the first people to notice the pattern was an immunologist at UCLA.

  • Between the fall of 1980 and the following spring, he saw a string of five patients,

  • all gay men in their 20s or 30s, with an unusual kind of pneumonia.

  • There was a fungus growing inside their lungs.

  • Normally, the fungus was totally harmless and would never infect the lungs, but in these

  • men it had, and it was making it hard for them to breathe.

  • The patients also had oral thrushbasically yeast infections in their mouthsand few

  • CD4 T cells.

  • By June, when the immunologist wrote up the results for the CDC’s weekly Mortality and

  • Morbidity report, two patients had died.

  • A month later, a dermatologist in New York chimed in with a similarly disturbing report,

  • this time with Kaposi’s sarcoma, a rare cancer where patients develop blotchy purple

  • lesions on their skin.

  • In two and a half years, 26 young gay men in New York and LA had been diagnosed with Kaposi’s.

  • Some also had the weird fungal pneumonia, and 8 had died.

  • It’s hard to imagine now, but at this point, scientists had no idea what was making people sick.

  • They didn’t know if it was some sort of toxin or a pathogen.

  • And if it was an infection of some kind, they didn’t know how it was spreading.

  • That meant they couldn’t warn people about how to protect themselves.

  • The association with gay men, though, was certainly striking, and early on, many called

  • the mystery disease GRID, for gay-related immune deficiency.

  • Lots of people would talk about it as thegay cancerorgay plague.”

  • But the disease wasn’t limited to gay men.

  • It was turning up in hemophiliacspeople whose blood doesn't clot properly and are

  • treated with clotting factors taken from other people’s blood.

  • Doctors were also seeing cases in IV drug users, women, infants, and heterosexual men.

  • In particular, 20 recent immigrants from Haiti had gotten sick, and none said they were gay.

  • Those clues were important, because they told scientists the diseasewhich had finally

  • been given the name AIDSwas probably infectious, and probably transmitted by blood.

  • There were other diseases that spread in similar ways, like hepatitis B.

  • So in March of 1983, the CDC issued a warning that doctors needed to be careful about blood

  • transfusions, and that the disease seemed to spread through both gay and straight sex.

  • Debates about the specifics, including whether it could spread through saliva, would happen later.

  • But what was the infectious agent?

  • The race was on for scientists to figure out what was causing the disease.

  • French molecular biologist Luc Montagnier suspected a virus because at the time, the

  • blood products hemophiliacs used were filtered for things like bacteria and fungi.

  • But viruses were too small to catch.

  • So along with his colleague Françoise Barré-Sinoussi, he searched cells taken from AIDS patients

  • and found a retrovirus.

  • Around the same time, Robert Gallo at the NIH in the US also identified a retrovirus

  • in samples from AIDS patients.

  • Both groups published their work in May 1983, and shortly afterward another team found yet

  • another retrovirus.

  • All the viruses had been given different names, and at first, it’s wasn’t totally obvious

  • that they were the same thing.

  • But they were, and in 1986, the cause of AIDS had been given an official name: HIV.

  • So, HIV was the problem, but where had it come from, and why had the epidemic struck

  • now, in the decade of big hair and Michael Jackson?

  • While some researchers were scrambling to identify whatever it was that made AIDS infectious,

  • others noticed that macaque monkeys also seemed to suffer from an AIDS-like disease.

  • One group decided to take some blood samples from these sick monkeys, and in 1985 they

  • found a virus that was similar to HIV.

  • It was eventually called SIV, for simian immunodeficiency virus.

  • Researchers started to think that HIV might have come from our primate relatives, jumping

  • the species barrier.

  • After a lot of work, they figured out that the virus behind the epidemic was very similar

  • to the chimpanzee version of SIV, and they were the ones who had passed it to us.

  • But how exactly?

  • There’s no real way to put this delicately, but most scientists agree that the reason

  • why SIV made the leap into humanswhat’s called a spilloveris because we had a

  • taste for bushmeat, or wild game.

  • In this case, monkeys and chimps.

  • This is known as the cut-hunter hypothesis.

  • In the course of butchering a chimpanzee, some SIV-infected chimp blood enters a small

  • cut on the hunter’s hand.

  • Or, a bit of blood splatters in their mouth.

  • The virus is close enough to human biology to infect the hunter, and over time, if the

  • hunter passes the virus along to enough people, it evolves into the HIV we know today.

  • Spillovers like these happened many timeswe can tell because the virus mutates

  • quickly, and by looking at genetic differences, we can identify multiple lineages of the virus,

  • each one corresponding to a spillover.

  • Weve traced the current epidemic to just one of these, called ‘M’ for main.

  • By analyzing chimpanzee pee and poop, researchers think the chimps who passed that version of

  • the virus to us lived in southwestern Cameroon, in the forests near the Congo.

  • And based on the oldest blood samples we can find that we now know have HIV in them, which

  • are from 1959 and 1960, scientists estimate that HIV-1 first infected humans around 1908.

  • If that seems like a long time ago, well, it takes a while for a virus to take off.

  • By the 1920s, it’s thought that the virus traveled downriverin a person, of course

  • to the burgeoning city of Kinshasa, then known as the Belgian colonial city of Leopoldville.

  • There weren’t many women around other than prostitutes, so experts think HIV spread that

  • way, and possibly through injectable drugs the colonists used to treat some tropical

  • and venereal diseases.

  • This was before disposable syringes, and nurses were trying to treat lots of people with just

  • a few of them, so the syringes may have only been rinsed with alcohol before being used

  • on the next patient.

  • So the very methods meant to stop the spread of disease may have actually been encouraging it.

  • With time, infected people in Kinshasa left to go to other places, and they did the unavoidable:

  • they brought the virus with them.

  • Because the virus mutates so quickly, we can group the viruses into 9 different subtypes

  • and get a sense of how HIV traveled around the world from Central Africa.

  • Several subtypes spread to other parts of Africa.

  • Subtype C went south and then landed in India.

  • Subtype B went to Haitiand then, through several quirks of history, came to the US.

  • First, in 1960, when the Belgians left the Congo, French-speaking Haitians started to

  • arrive in the Congo to work as doctors, lawyers, and other professionals.

  • But with the creation of Zaire in 1965, the immigrants felt unwelcome, so they went back

  • to Haiti, bringing HIV with them.

  • There, HIV expanded especially quickly, possibly because of a plasmapheresis center where people

  • could get paid to donate their blood plasma.

  • The center used a machine that mixed the blood of different donors, allowing viruses to transfer.

  • By 1982, nearly 8 percent of a group of young mothers in a Port-au-Prince slum were HIV-positive

  • an astoundingly high number.

  • HIV is thought to have entered the US around 1969, with just one infected person or unit

  • of plasma from Haiti.

  • It took about a decade for anyone to notice, but by then it was too late.

  • The epidemic had begun, and HIV was not only in the Americas, but Europe and Asia, too.

  • And now that it was here, we needed to figure out how to fight it.

  • But we'll get to that in the next episode of this mini-series.

  • In the meantime, thanks for watching this episode of SciShow, and if you want to learn

  • more about HIV and all kinds of other science, you can go to youtube.com/scishow and subscribe.

Here at SciShow, we talk a lot about the fascinating, complicated, and often very weird stories

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B1 中級 新型コロナウイルス 新型肺炎 COVID-19

病気のチンパンジーが世界的なパンデミックに至った経緯HIVの台頭 (How a Sick Chimp Led to a Global Pandemic: The Rise of HIV)

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    林宜悉 に公開 2021 年 01 月 14 日
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