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  • You are part of one of the world's greatest endeavors: the effort to stop infectious disease.

  • Like other animals, infectious diseases have been with us since the dawn of our species,

  • from herpes virus that infected our common ancestors in Africa

  • to the Covid-19 pandemic that struck the whole world.

  • The effort to understand these diseases has been going on for some time, too.

  • As far back as 400 BCE, civilisations in different parts of the world tried to work out

  • who became ill and why.

  • Since then, we've come a long way in understanding what diseases are and how they spread.

  • And that knowledge is vital to stopping them.

  • But it's not only doctors and scientists who can act on what we know.

  • Infections involve individual people,

  • so everything from the way you and I go about our everyday activities

  • to the way we organise whole societies all influence how an outbreak evolves

  • and whether we overcome it.

  • I'm Pardis Sabeti, a professor of genetics at Harvard University,

  • where I study infectious diseases.

  • In this series, we're going to take a deeper look at disease outbreaks,

  • from the microbiology and genetic factors behind them to healthcare systems,

  • social structures and people who tackle them, including you!

  • Welcome to Crash Course Outbreak Science!

  • [Theme Music]

  • The study of outbreaks is a little different from your garden variety science.

  • Not everything about an outbreak can be studied experimentally.

  • Outbreaks are complex situations involving real people in their environments,

  • so we can't perfectly measure and control all the variables.

  • It would also, you know, be highly unethical to release an infectious disease into a population

  • just to study what happens

  • though, sadly, that hasn't stopped people from doing just that.

  • Even so, it helps to be specific about what we're talking about when using words like

  • epidemicsandoutbreaks”.

  • The American Public Health Association's Control of Communicable Diseases Manual

  • yes, there's a handbook for this! –

  • defines an epidemic as:

  • The occurrence, in a defined community or region, of cases of an illness

  • (or an outbreak)

  • with a frequency clearly in excess of normal expectancy.”

  • In other words, an epidemic is when many more people in a group than usual develop a particular illness.

  • We can also use the wordoutbreak”, usually when the region we're talking about is relatively small.

  • That might all seem straightforward, but there's a question hidden here.

  • What counts as a “usualamount of illness?

  • It turns out, it depends on the community.

  • For example, in the 1990s there was an outbreak of cholera in Latin America.

  • Cholera is a bacterial disease that attacks the intestines,

  • usually contracted from contaminated water, and nearly a million people were infected.

  • Those kinds of numbers for cholera cases hadn't been seen on the continent in over a century,

  • so the sudden rise was dramatic.

  • But near the Ganges delta between Bangladesh and India,

  • cases of cholera are an unfortunate and persistent fact of life because of the environment.

  • When a disease has roughly the same incidence in a place over an extended period of time,

  • it's called endemic.

  • The word endemic is derived from the ancient greek wordsenmeaningin

  • anddemosmeaningpeople”, like, diseases that reside in a group of people.

  • That's opposed toepidemic”, which is derived fromepimeaningon”,

  • as in, diseases that act on a group of people.

  • Similarly a pan-demic draws on the greek wordpanmeaningall”,

  • as in an epidemic that spreads across borders into many countries,

  • affecting the whole world if left unchecked.

  • What really distinguishes an epi-demic, or outbreak,

  • is that the number of cases of illness are much higher than they normally are within

  • a certain community.

  • Which means words likenormalandusualhave to be taken in the context of particular groups of people,

  • their way of life, and circumstances.

  • It doesn't mean that the cases of cholera were more or less important in South America

  • than in the Ganges Delta.

  • But it means we might approach the two situations differently.

  • Outbreaks are evolving situations where the disease could become more widespread.

  • So the goal is to stop the disease spreading even further, as well as treating those who have it.

  • It also means having organizations and systems in place that can handle the social changes

  • an outbreak requires.

  • Which is a pretty tall order!

  • What's key to tackling those challenges is understanding the nature of an infectious

  • disease and how people respond to them.

  • We'll start with the disease itself.

  • When it comes to diseases, different scientists have different ways of thinking about them.

  • For example, microbiologists consider diseases in terms of their biological cause.

  • One of the most important scientific discoveries in history is that tiny organisms that enter the human body

  • are what's often responsible for us contracting infectious diseases.

  • These are known as pathogens.

  • The most commonly known pathogens are microorganisms like bacteria, viruses, protozoa and fungi.

  • The science behind pathogens is pretty broad,

  • so we'll be looking at them in closer detail next episode!

  • The take-away is that microbiologists tend to characterize diseases by the pathogens that cause them.

  • Epidemiologists meanwhile think about diseases in terms of the bigger picture,

  • focusing on how it spreads and what its source is.

  • Unfortunately for us, there are lots of ways pathogens can infect people.

  • They might be spread from person to person through contact with skin

  • or through droplets in the air from someone's sneezes or coughs.

  • They might be eaten in contaminated food or injected by an insect like a mosquito.

  • Even if the pathogens might be different,

  • an epidemiologist would think of diseases in terms of these transmission routes.

  • They also consider when a community is regularly coming into contact with the same source of

  • disease, which are called reservoirs.

  • Sometimes, a reservoir is a group of infected people,

  • but it could also mean a local population of animals carrying diseases like rabies.

  • The reservoir might be soil which contains certain kinds of fungi or contaminated water.

  • The kind of reservoir also determines who might be at the most risk from an outbreak,

  • as we'll see in a moment.

  • Finally, there are medical scientists and doctors,

  • who tend to think of diseases by their clinical symptoms.

  • Clinical symptoms might be familiar things like fever or difficulty breathing but also

  • could be conditions like, say,

  • inflammation and swelling of body parts or a whole lot of other not-so-fun things.

  • From a doctor's perspective, identifying diseases by their symptoms is important for treating them.

  • It's worth mentioning we're going to have to be frank about the human body

  • and some of the more icky parts when studying outbreaks.

  • But science demands clarity!

  • For example, in the case of diarrhea, regardless of the pathogen or the way the patient was infected,

  • they need to be treated with fluid replacement to keep them hydrated.

  • So we have three ways of looking at disease:

  • the organism behind the disease, the way it spreads, and how it affects an infected person.

  • Which brings us to the role people play in an outbreak.

  • Different perspectives of disease help inform groups like healthcare providers,

  • public health experts and the communities themselves to tackle outbreaks.

  • To see how this all comes together, let's look at a real life example.

  • We've mentioned that cholera is endemic to the Ganges Delta,

  • just off the coast of West Bengal in India.

  • Although it's endemic in the whole region,

  • scientists can still identify outbreaks in a given community,

  • exceeding their expected number of cases.

  • Let's go to the Thought Bubble.

  • On October 13, 2004, a healthcare facility in Kanchrapara, India,

  • reported a cluster of cases where patients suffered from acute, watery diarrhea.

  • As I said, science needs clarity!

  • A lot of those patients also were so dehydrated they were sent to the hospital

  • all classic signs of cholera infection.

  • The district epidemiologist set about to confirm whether this was an outbreak.

  • He started by looking at the data of similar diarrhea cases from the previous months

  • and found that the number of cases in the cluster was in fact higher than expected.

  • To confirm that the patients definitely had cholera, he worked with the hospital to take samples,

  • which, for clarity, were from the patients'... butts.

  • The samples were from their butts.

  • Those samples were sent to a lab, where microbiologists could test them and rule out other pathogens

  • that might be responsible too, like salmonella.

  • Meanwhile, the epidemiologist drew a map of the cases by household.

  • He found that most of the cases came from areas which relied on the municipal water supply.

  • In fact, a nearby area that used a different water supply had fewer cases.

  • It turned out that earlier that same month,

  • the municipal water supply had sprung a leak in its pipeline.

  • That was a major clue.

  • A leak would make it possible for fluids to be sucked into the pipeline and contaminate the water.

  • What's more, it had been raining heavily at the time,

  • bringing lots of sewage-contaminated water near the pipeline.

  • Sure enough, the lab results came back positive for Vibrio cholerae,

  • the bacteria that causes cholera, and negative for other pathogens.

  • At that point, it was clear there was a cholera outbreak on their hands.

  • Thanks, Thought Bubble!

  • A later environmental assessment with the city's engineers found that, as suspected,

  • the leak in the pipeline had sucked up sewage-contaminated water into the water supply.

  • Thankfully, by that point the leak had been repaired and water had been chlorinated.

  • And shortly after the intervention, the number of new cholera cases had fallen rapidly!

  • We can see how different perspectives on disease helped identify and resolve the outbreak.

  • The clinicians monitoring clinical symptoms helped bring the high number of diarrhea cases to light

  • and flag up the possibility of cholera.

  • Microbiologists confirmed this by identifying the pathogen from lab testing,

  • while epidemiologists identified the reservoir for the disease.

  • While outbreaks are specific to certain groups of people,

  • the way in which they happen is often starkly similar to outbreaks all over the world.

  • While we've mentioned cholera outbreaks in Latin America and India so far,

  • one of the most famous ones happened 150 years earlier in London, England.

  • Though the tools at his disposal were a little different in 1854,

  • physician John Snow used many of the same methods that the district epidemiologist in

  • Kanchrapara used to identify the outbreak.

  • Snow also used a map to trace the locations of each cholera case to find the common source of infection.

  • Turns out, a contaminated water pipe was the culprit of that outbreak, too.

  • Contemporary outbreak scientists still map all kinds of outbreaks,

  • often with advanced geospatial techniques and software,

  • including NASA earth observing research satellites.

  • And in both Kanchrapara and London,

  • the reservoir also highlighted who was susceptible to certain kinds of outbreaks.

  • It was clear that those who relied on the municipal water supply were already exposed

  • to risks from the unfit water system, even before the outbreak.

  • And we'll see throughout the series,

  • environmental conditions play a huge role in determining how often outbreaks occur and

  • who is affected by them.

  • But people and practices were also at the heart of the outbreak response.

  • In Kanchrapara, monitoring and collecting data from healthcare facilities

  • required social practices that encouraged reporting unusual scenarios, like a cluster of symptoms.

  • There were also organizational links between healthcare facilities and epidemiologists

  • that made sure information was flowing in a useful way.

  • Transporting the samples and having laboratories equipped to analyse them required locally

  • available technology and infrastructure.

  • Even before the outbreak, decisions had been made to have an epidemiologist in the area

  • and labs with the capacity to test for cholera in the first place!

  • After the outbreak, scientists worked with hospital clinicians, city water engineers,

  • district authorities and the chief medical officer to plan for next steps.

  • That included an investigation of the city pipelines for leaks so they could be fixed

  • before the next outbreak

  • and making sure the water was chlorinated from that point on to prevent cholera infecting the supply.

  • Which brings us to a final point about tackling outbreaks: communication.

  • Different groups, from patients, scientists, governments and public health workers,

  • need to share information and collaborate during an outbreak to ensure the right steps are taken.

  • Throughout this series, we'll continue to look at how the way people interact with one another

  • and the social structures they inhabit all play a role in how outbreaks develop and how we can stop them.

  • And hopefully, what we learn in this series will enable you to play a role too.

  • Next time, we'll get into the microscopic world of pathogens.

  • See you then!

  • We at Crash Course and our partners Operation Outbreak

  • and the Sabeti Lab at the Broad Institute at MIT and Harvard

  • want to acknowledge the Indigenous people native to the land we live and work on,

  • and their traditional and ongoing relationship with this land.

  • We encourage you to learn about the history of the place you call home through resources

  • like native-land.ca and by engaging with your local Indigenous and Aboriginal nations

  • through the websites and resources they provide.

  • Thanks for watching this episode of Crash Course Outbreak Science,

  • which was produced by Complexly in partnership with Operation Outbreak

  • and the Sabeti Lab at the Broad Institute of MIT and Harvard

  • with generous support from the Gordon and Betty Moore Foundation.

  • If you want to help keep Crash Course free for everyone, forever,

  • you can join our community on Patreon.

You are part of one of the world's greatest endeavors: the effort to stop infectious disease.

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B2 中高級 美國腔

----(What Is Outbreak Science? Crash Course Outbreak Science #1)

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    大文 發佈於 2022 年 02 月 04 日
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