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A sad reality that we have to face when studying outbreak science is that sometimes groups of people use outbreaks intentionally to inflict harm on another group. We call this "weaponizing an outbreak", and it's the focus of this episode of Crash Course Outbreak Science. In this episode we'll look at how different groups have weaponized outbreaks throughout history, and the consequences, and we'll discuss what we can learn from those cases to prevent bioweapon attacks in the future.

This episode of Crash Course Outbreak Science 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.


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Earlier in this series, we saw how  violent clashes between groups of people can cause outbreaks.

In conflicts like war, the  collateral damage to infrastructure and the precarious living conditions it subjects  people to makes outbreaks much likelier. Although they’re linked to  the violence, in these cases, disease is a sort of terrible  side-effect of the conflict itself.

Sadly, there are also times when certain  groups might intentionally use an outbreak to inflict harm on another group of people. The latter is what we call  weaponizing an outbreak, and it’s been going on for  longer than you might think. In this episode, we’re going to look  at when outbreaks become weapons, from the past to the present,  and what we’ve learned from them.

I’m Pardis Sabeti, and this is  Crash Course Outbreak Science! [Theme Music]. Before we get into things,   we should mention up front that this  episode goes into challenging topics involving violence like  war, genocide and terrorism. But we think it’s important to understand the  context in which outbreaks are weaponized, so that we know where the risks lie and  how we might stop it from happening.

Historically, people have used naturally  occurring outbreaks to hurt certain populations by making them sick or die from a  disease, and from the chaos that follows. But in modern times, “weaponizing outbreaks”  tends to mean artificially releasing a pathogen to spread and infect a group of people. Outbreaks can also be weaponized  against animals and crops, to attack resources that people rely on, but we’re going to focus on the kinds  of outbreaks that infect people.

Because they rely on biological  mechanisms to inflict harm, unlike the physical damage from, say, a bullet, weaponized outbreaks are also called bioweapons. Like much of the horror  that humans are capable of, there’s no easy explanation for why people  want to inflict terrible things on each other. Answering that is a complex,  philosophical and social question that has been debated for as  long as humans have been around.

But history can at least give us the  context in which bioweapons have been used and how they might be used today. That tends to be the same  context as ordinary weapons: to hurt or eliminate groups  of people during a conflict. Remarkably, people have used bioweapons  since long before we knew pathogens, the germs that make us ill, were  responsible for infectious disease, or even knew what pathogens were!

In 1346, a bacterial disease known as  the bubonic plague, or “Black Death”, had crept into Western Europe. The victims had flu-like symptoms and “buboes”, visibly swollen bumps in the armpits or  groin, which was usually followed by death. And at the same time Caffa, a city on the  coast of the modern day Crimean Peninsula was under siege by our favourite exceptional  empire here on Crash Course… the Mongols.

Today we know that the plague spreads  through a bacterium transmitted by fleas, but at the time the prevailing  theory was that “miasma”, a kind of toxic cloud, made people  sick when they breathed it in. So, according to historic accounts, since the Mongols had plenty of access to   the infected corpses of plague  victims from their own ranks, they loaded up catapults with the  corpses and hurled them into the city. As one observer at the time wrote, the  intention was to kill off those inside, because the “intolerable  stench” of the corpses’ miasma   would spread the disease into the air and water.

In reality, it’s the bacteria that would  have spread to the citizens of Caffa as they handled the corpses while  removing them from the city. Either way, it’s pretty gruesome stuff... ... And, by the same account at  least, it was pretty effective!

People inside the city did become infected  and likely because of the Mongols’ efforts. So we can see that one way that  people have weaponized an outbreak is to attempt to start one  that affects your enemies. Another army tried this over  4 centuries after the Mongols.

In 1763, the British Army was locked in  battle with Native Americans at Fort Pitt, in today’s Pittsburgh, Pennsylvania. To devastate the Native Americans he was fighting  against, the British General Jeffrey Amherst plotted to spread smallpox by arranging  for traders to distribute infected blankets from a nearby hospital to the Native Americans. It isn’t clear whether the infected  blankets did actually spread smallpox, and if they did, the death toll was  likely less than a hundred people.

But the intention was clear: to start a smallpox outbreak that would kill the  Native Americans fighting against the British. And sometimes, when a natural outbreak occurred, colonizers weaponized them by  deliberately not helping those affected. In the early 1860s, a few smallpox cases  broke out in today’s Vancouver Island, and the British colonizers chose  not to implement a strict quarantine or pursue a strong vaccination program, either of which could have  helped kept the epidemic at bay.

And so, it spread to the First  Nations people living nearby. Though efforts were made by  some colonizers to help them, mostly they looked to protect themselves. When the disease broke out more seriously  in the First Nations population, they were forced out of the town, and  their homes were even set on fire.

As one journalist wrote at the time: “...every precaution is used in order  to confine the disease to the natives”, while celebrating that “Only one death  has occurred amongst the whites.” Over the next year, thirty thousand  First Nations people would die, paving the way for more land  to be taken by the colonizers. Although the colonizers didn't  start the outbreak, their inaction, followed by forcibly removing First  Nations people from the towns, worsened the effects of the outbreak  on them and reduced their population, to the benefit of the colonizers. As well as driving people from their homes, forcing a group into a single place with poor  environmental conditions can have a similar effect by encouraging outbreaks to happen.

At the start of World War II in 1939, the  Nazis laid siege to the Polish city Warsaw, damaging the sewage system and  contaminating the water supply. That led to a small outbreak  of the bacterial disease Typhus which eventually disappeared  in the summer of 1940. By then, the Nazis occupied the city.

The Nazis used the potential of another  epidemic to justify creating the Warsaw ghetto, a small section of the city which Jews were  forced to live in and forbidden to leave. They surrounded the whole area with a  three metre wall topped with barbed wire and stopped food supplies from entering, trapping  everyone in overcrowded and unsanitary conditions. The results were catastrophic and led to  another, even bigger outbreak of typhus.

The Nobel Prize winning biologist  Ludwik Hirszfeld, would later say,   based on his time in the ghetto: “Typhus was created by the Germans,  precipitated by lack of food, soap, and water, and then—when one concentrates  400,000 wretches in one district, takes everything away from them, and gives  them nothing, then one creates typhus. In this war, typhus is the work of the Germans.” Refusing to recognise that  they caused the epidemics, the Nazis took it as a  justification to do even more harm. During the war, the Nazis would continue to  claim the genocide of 3 million Jews in Poland “was unavoidable for reasons of public health”.

As for the Typhus outbreak in the Warsaw ghetto, just when it should have gotten worse as  winter hit, it actually started receding. That’s because the Jews inside  the ghetto smuggled food in and   ran community kitchens to fight starvation. They also formed communities of medical  workers and taught health education and hygiene practices in the midst of the war, implementing their own healthcare initiatives to  fight back against the outbreak inflicted on them.

By September 1942, the outbreak was over. As the war continued, countries like Japan, the US  and Britain were using the knowledge of pathogens to create weapons that could  artificially spread a disease. And shortly after the war, some had even  developed bioweapons as we recognise them today.

As best we know, they’ve never been used  in an open conflict between countries, but the general design of modern bioweapons   relies on producing a significant  amount of a given pathogen in a lab and storing it in some kind of vessel, before releasing the pathogen into  a target population to infect them. It’s likely that would be by dispersing  them into the air as a kind of spray where they could be inhaled or absorbed into   wounds or by contaminating  a source of food or water. The kinds of pathogens used in a bioweapon can  be reproduced from naturally occurring ones, like the viruses that cause smallpox viruses  or bacteria that cause anthrax and cholera.

But advances in biochemistry have  made the process even more fine tuned. Scientists can pick particular strains of a  disease and even genetically engineer new ones using gene editing technologies like CRISPR. That lets them hand craft pathogens  with a higher level of infectiousness, deadliness and resistance to treatment.

Bioweapons have other properties that  would make them particularly dangerous. Unlike other weapons, they  could be used stealthily, making them harder to detect  until people are already infected. What’s more, because the disease can spread, bioweapons could affect areas far beyond  the vicinity of the original attack.

Though that could be a disadvantage  if the disease eventually makes its way back to the attacking force! After all, the spread of outbreaks  aren’t always predictable. In 1969, the WHO estimated that a single  bioweapon attack in a medium sized city could kill tens of thousands of people.

Given the rising tensions of the Cold War and  growing capacity to unleash such an attack, in 1972, a treaty known as the  “Biological and Toxin Weapons Convention” was signed and ratified by most of the world’s  countries, including the US and the Soviet Union. It prohibited the development, production, and stockpiling of pathogens for  anything other than peaceful purposes. Today, the convention is still the final  word as far as it’s signatories are concerned but unfortunately, it hasn’t been enough.

States have continued to develop bioweapons, and the availability of biochemical techniques  mean that smaller groups like terrorist cells could potentially develop a bioweapon,   as part of a bioterrorist attack. Plus, there’s always the risk of an accident. In 1979, a plume of anthrax  spores was accidentally released from a secret bioweapons facility in  Sverdlovsk, a city in the Soviet Union.

It drifted over fifty kilometres and  killed at least sixty-six people, the deadliest human outbreak  of inhalation anthrax ever. Even when they’re working with viruses  for peaceful purposes, like vaccines, there’s a risk labs might also have  samples stolen and turned into a bioweapon, or simply mishandled and let loose! So naturally, there are strong security measures  for labs that handle dangerous pathogens, from limits on who can access them to  security protocols for moving samples around.

This is called biosecurity. That’s just one part of a lab’s  overall biorisk management, the strategies that help prevent accidents  and attacks, keeping everyone safe. We can also regularly monitor areas that are  likely targets of an attack, like water supplies, for pathogens that could lead to an outbreak, so that we can quarantine them or  cut off the source if we find any,   which could stop an attack quickly.

We can also make it easier to  trace the source of an attack to make it easier to respond and harder  for the attackers to remain anonymous. That makes a bioweapon less appealing to use. For example, analysing the genes of  a weaponized pathogen as it spreads could give us clues as to where it came  from, based on the mutations it develops.

This could give us a kind of breadcrumb  trail to trace back to the original case, and where the attack may have started. Finally, research is continuing on how to  prepare in case such an attack happens. Like other kinds of outbreaks, it means developing  the capacity to spot an outbreak early on, recognize the disease causing it,  stopping it spreading any further and having treatments to help infected patients.

While a lot of this work  happens in a lab, sometimes, governments even act out  simulations of outbreaks to practice and see how well their strategies  would work in the real world! All of this can help reduce the impact of an  outbreak, and even stop them in their tracks. As we mentioned earlier, there’s  no easy explanation for why people   weaponize outbreaks to hurt each other and frankly, it’s upsetting to think about.

But by learning about threats like these  and the ways we can respond to them, we can also express the best of  humanity’s qualities by coming together and helping stop outbreaks,  wherever they may arise. And tackling these challenges is  exactly what we’ll be covering   through the rest of the series. 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 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.