Episode 28: Smallpox Blankets

The story of smallpox blankets offered as gifts to indigenous peoples as a weapon of war is ubiquitous — but is it based in truth? And did our increased medical understanding of smallpox lead to its use as a biological weapon?  In this episode, we confront these questions and explore the history of biological warfare, smallpox, and medicine. Listen to all this, a new #AdamAnswers, and more in this episode of Bedside Rounds, a tiny podcast about fascinating stories in clinical medicine.


  • Barras V and Groub G, “History of biological warfare and bioterrorism,” Clin Microbiol Infect 2014.
  • Carus W, “The history of biological weapons use: what we know and what we don’t,” Health Security, Vol 13, No4, 2015.
  • Fenner F et al, “Smallpox and its Eradication,” World Health Organization, 1988, Chapters 5 and 6.
  • Mayor A, “The Nessus Shirt in the New World: Smallpox Blankets in History and Legend,” J Am Folklore, Vol. 108, No. 427 (Winter, 1995), 54-77.
  • Mear C, “The origin of the smallpox outbreak in Sydney in 1789,” Journal of the Royal Australian Historical Society, June, 2008.
  • Skwarecki B, “What is the scariest disease?” PLoS Blogs, retrieved at https://gizmodo.com/what-is-the-scariest-disease-1653943826
  • Theves C, et al, “The rediscovery of smallpox,” Clin Microbiol Infect 2014; 20: 210-218.
  • Ranlet P, “The British, the Indians, and Smallpox: What actually happened at Fort Pitt in 1763?”, Pennsylvania history: 427-442.
  • Warren C, “Smallpox at Sydney Cove — who, when, why?” J Aust Studies, 30 Oct 2013



This is Adam Rodman, and you’re listening to Bedside Rounds, a tiny podcast about fascinating stories in clinical medicine. This episode is the first of a two-parter episode, and it’s called “Smallpox Blankets.” We’re going to talk about the mysterious origins of smallpox, how humans learned to fight the disease, and how this knowledge was turned into a weapon of war, especially against indigenous peoples. 


I want to start with a story. High in the Andes mountains, an emissary from a faraway land has come seeking an audience with the King. Clad in a black cloak and bearing gifts, he is eagerly invited into the king’s court. Among the treasures he brings is a small locked box that only the king can open. After providing the key, the emissary slinks away from the court. Eager to see what this delights this strange man has brought, he unlocks the box in the middle of his court. The box swings open, and a mysterious substance flies out “like scraps of burning paper.” One by one, the courtiers and the king fall ill. Soon they are covered head to toe in “burning scabs”. The disease brings death, and quickly spreads among the people of the kingdom. Soon after the armies of the Spanish arrive, easily vanquishing those that the disease spared.


The story is almost certainly apocryphal — but to those in the waning years of the great Empire of the Inca and the beginning of Spanish colonialism, it felt viscerally real. This particular version dates to 1613, written by a Spanish-speaking native in Peru preserving what was presumably a long-standing myth. A disturbingly similar legend is told by the Ottawa Indians in the Great Lakes region. After aiding the French against the British in what we Americans call the “French and Indian War,” the Indians were sold a small tin box, which they were instructed to not open until they reached home. The tribe followed the instructions. Inside was a second tin box, and then another, then another — a Russian doll until the last was opened to reveal “nothing but mouldy particles.” Soon after, the tribe became ill with a “terrible sickness”. This is purported to have happened in 1757, though the legend was recorded in print in 1887.


These legends certainly take on a certain mythic quality — poisoned gifts, treachery, foreign conquerers. But are they based in truth? Was colonialism of the New World allowed by biological warfare on a massive scale? And to what degree did our medical understanding of smallpox allow for this? 


The find out we’re going to have to go back to the very beginning — to the beginnings of smallpox, and to the beginnings of war Smallpox is fundamentally a disease of civilization. The virus has no natural reservoir but humanity, and requires a certain amount of concentration to spread. It probably started in either ancient India or Egypt. In the beginning of the 20th century, there was a paper published detailing three “smallpox mummies”, still covered in the lesions dating to 1500 BCE; but the mummies themselves were lost in the chaos surrounding the Great War. Plenty of contemporary Egyptian mummies do show telltale pockmarks though, including Ramses V. Again, it’s unclear when smallpox appeared on a grand scale; there’s always active debate that this or that ancient plague might have been smallpox, but nothing convincing has emerged. In fact, for a disease that would ravage humanity, there are no definitive references until the fourth century CE in China, and not until the 10th in the Mediterranean. Both these doctors — Ko Hung in China and al-Razi in Asia Minor — clearly define smallpox as a disease of children, a sign that they were endemic in these regions for at least several generations. In this case, the silence on smallpox probably suggests the disease didn’t start spreading until fairly late in civilization; doctors in China, India, and the Mediterranean left plenty of detailed descriptions of modern diseases — including epidemics like bubonic plague. This suggests that smallpox didn’t start spreading widely until the first couple centuries CE, first pushing into China, then the large cities of the Mediterranean and Middle East, and finally into the still relatively sparsely populated Europe. By the 10th century CE, smallpox had spread broadly across the Eurasian continent and North Africa, its spread further south only stopped by the mighty Sahara desert in Africa, and the seas of Southeast Asia. The human cost was staggering. In the last millennium, it’s been responsible for roughly 10% of ALL human deaths. And don’t think the invention of vaccination stopped that — half a billion of those deaths were in the twentieth century. 


And these were horrible deaths. After exposure, victims would get flu-like symptoms — high fevers, chills, and body aches. Then a splotchy rash would break out all over the body. After a few days, the rash would blister. For some, blood would start oozing from these pox and you’d be dead within 24 hours. The lucky were permanently scarred with  pockmarks. The next time you’re at an art museum, or looking at photos from the nineteenth century, take a close look at the faces. Pock-marked faces were ubiquitous until fairly recently. The effects on society, as you could imagine, were massive. In both India and Europe, there were common sayings that children should not be considered for inheritance until they had survived smallpox. There was a pantheon of gods dedicated to smallpox. You’ve probably never heard of St. Nicaise, but he was the patron saint of smallpox and very popular in Catholic countries prior to the 20th century. Among the Yoruba in West Africa the worship of Sapona, the smallpox god, was so common and fearsome that the colonial British outlawed it — and worship of the deity was identified as a barrier to universal vaccination in the 1960s, two centuries later. And in China, T’ouShen Niang-Niang, a god identified with the historical nun who introduced variolation, the first effective prevention of smallpox, was the most commonly worshipped deity in China in the nineteenth century. 


Up until the massive population growth in cities in the 19th century, smallpox would flare on 5-7 year intervals in endemic areas, and occasionally spill over to areas where it wasn’t endemic. Temple records in Japan have proven to be a valuable source of this historic information. In a small village on the island of Honshu, for example, we know that one of these smallpox flares infected 1200 people in a nonimmune population of 1400, and 460 people died. That’s a case-fatality rate of 38.3%. Imagine that happening regularly throughout your life.


And things would get a lot worse when smallpox left the confines of Eurasia. Spanish and Portuguese colonialists, seeking glory, god, and plenty of gold, set sail for the recently discovered New World. The indigenous peoples of this new territory lived in a complex and urban society — arguably, the Inca civilization was the largest the world had ever seen, despite lacking writing, the wheel, and pack animals. Their ancestors had migrated over the antediluvian land bridge that had once connected North America and Asia, and this bottleneck effect spared them the diseases that had wrecked Eurasia — but also the natural immunity. The Spanish and Portuguese brought plenty of horrors to the people of the Aztec and Inca empires — slavery, murder, plunder, rape, systematic destruction of their culture. But bringing smallpox may have been the worst. The Spanish kept records, so we can estimate that about 25 million Aztecs lived in the area now Mexico and Central America prior to the Spanish conquest. Just 10 years later, after the spread of smallpox, there were only 16.8 million. From here, we can get the context of the Inca folk tale of the black-clad emissary from the beginning of the episode. From modern Mexico, smallpox burned its way south into Inca territory. By 1524, an outbreak killed 200,000 people in the Empire, including the king and his immediate successor. The Empire was thrown into chaos, and Pizarro and a small band of Spaniards — apparently only 40 of them — easily conquered Cuzco and killed the last heir of the Empire ten years later. 


The natives of North America were spared for a time, until the British started forming colonies on the Atlantic seaboard. Unlike the Spanish and Portuguese, the British killed and chased away locals, so we don’t have great records. But contemporary estimates suggest that outbreaks of smallpox rapidly killed ½ to ⅔ of the Indians in British territory. 


The history of this first wave of colonialism often omits how essential smallpox was to European conquest of the New World. Not only were large swathes of the population rapidly killed, but the locals would dissipate to escape the disease, spreading the plague further. Men of fighting age were decimated. Pregnant women and children were especially vulnerable, disadvantaging the next generation. Power structures were smashed, making resistance more difficult.  I’m no historian, but I have to imagine had there been endemic smallpox in the New World, the current map of the Americas might look very different.


The big question, of course, is whether this spread of smallpox was natural, just as it spread over the Eurasian continent the millennium before, or a deliberate act of biological warfare.


In order to answer this, we need to look at the history of war. Biological warfare, narrowly defined as weapons using toxins or biological agents, has been around since the beginning of civilization. Anthropologists in the 20th century have shown that a variety of indigenous peoples in disparate parts of the world use toxin-tipped arrows and darts as part of hunting. The best documented ancient example is of Scythian arrow poison. It was a mix of dead vipers and human blood, buried in a dung heap and allowed to putrefy. Aristotle described it as “corrupted blood,” and Pliny matter-of-factly stated that “this nefarious practice makes a wound incurable — by a light touch it causes instant death.” Modern recreations of this “recipe” have shown that this would likely contain clostridium tetani — tetanus — and bacillus species — including anthrax. Poisoned arrows survived into the middle ages until the advanced killing power of the longbow made extra poison unnecessary. But biological warfare in the sense we know it, using an infectious agent to kill a population, was the exception rather than the rule until recently. The historian Carus has performed an exhaustive review of claims of ancient biological warfare. Many of the supposed cases appear to be more myth than fact, or were attempts at poisoning water supplies, which isn’t truly biological warfare since the intent is to prevent people from drinking, rather than making them sick. In fact, he identified only one credible case from this period — the Mongol Siege of Caffa in Crimea, where victims of the bubonic plague were catapulted into the city, and an outbreak of bubonic plague was soon after noted.


The only credible case, I should mention, until the smallpox outbreaks in the New World. Carus starts with the story I opened with — that Pizarro provided a box with scraps of smallpox infected clothing, killing the Inca king, prior to conquering Cusco. This, he concludes, was likely apocryphal, and this initial spasm of smallpox was probably part of its natural spread.


But stories of the Spanish spreading contaminated clothes and blankets spread throughout the terrified peoples of central and South American, at least as recorded by folklorists centuries later. But that may be because of the actions of another colonial power.


The first definitive documented use of smallpox as a weapon happened much later, long after the natives of the southern environs of the American has been crushed.  It was 1763, and the chief Pontiac of the Great Lakes region had aligned his people with the French to fight British encroachment in his territory. The English were besieged at Fort Pitt, then a remote backwater on the frontier but which is now near Pittsburgh. The situation looking increasingly desperate, the British commander Jeffrey Amherst, wrote to the local commander Henry Bouquet in a correspondence that still exists. “Could it not be contrived to send the smallpox among the disaffected tribes of the Indians? We must on this occasion use every strategem in our power to reduce them.” Bouquet responded, “I will try to inoculate them with some blankets that may fall in their hands, and take care not to get the disease myself.” While it’s unclear that Amherst’s orders made it to the fort in time, it didn’t much matter — later that summer, two of Pontiac’s men came to the fort for peace negotiations. William Trent, a trader, documented what happened next. After discussion, the two men asked for a “little provisions and liquor to carry us Home.” Trent writes that, “we gave them two blankets and an handkerchief out of the Small Pox Hospital. I hope it will have the desired effect.” And apparently it did, because weeks later, the disease tore through besieging natives, allowing Bouquet to rout them and relieve the fort. The event didn’t go unnoticed by his superiors, who recognized that using smallpox as a weapon was something new, outside the confines of traditional warfare — though to be clear, not inappropriate against a native population they considered inferior. And they were right. In retrospect, white — and especially British — use of smallpox against indigenous peoples is the birth of modern biological warfare.


That smallpox as a weapon would start emerging in the latter half of the 18th century is no historical fluke. During this period, there was a dramatic increase in the medical understanding of how to treat the disease, especially in Britain, that would culminate with Jenner’s invention of vaccination in 1796. Doctors had long noted that those who were pockmarked couldn’t be infected again by the disease. Sometime towards the end of the first millennium CE, it was noted, probably by accident, that those who were infected with smallpox by the cutaneous route — that is, by having pus or a scab get directly into a cut in their skin — would suffer a far more mild and localized version of the disease. By the 10th century CE, the Chinese were grinding up dried scabs and inhaling them in secret religious rites to protect people from the disease, and by roughly 1500 this would become part of standard medical practice there. The process also started apparently independently in India, where practitioners would prick children with a needle dipped in smallpox pus. This method is now called “variolation,” a modern name to differentiate it from vaccination, though doctors at the time used horticultural terms like engrafting or transplanting. Variolation would cause a large, pus-filled primary lesion with smaller satellite lesions. I’ve posted some great images on Twitter of these from the 19th century. Variolation was far safer that a primary infection, and it too would confer a lifelong immunity to smallpox, but it still had major problems. First of all, the case fatality rate was between 0.5-2% given the strain, which is great compared to the 30-70% for smallpox, but still pretty bad for a preventative treatment. And this was not an attenuated, or killed, virus — variolation could cause local outbreaks of “natural” smallpox since these lesions were infectious. And in the societies in which it developed, variolation was used to protect individuals — and of course, the true power of vaccination is to protect entire societies by decreasing natural reservoirs of disease.


From India, variolation spread to the Ottoman Empire, where Europeans came into contact with the idea. The British, in particular, were ardent converts. In 1714, an influential report on Chinese variolation was presented at the Royal Society in London, and soon after statistical analysis confirmed its protective effect. The process caught on like wildlife. Only six years later, the royal princesses were being variolated, and by 1746, the London Smallpox and Inoculation Hospital offered free variolation for all. By the 1790s government plans were drawn up to eliminate smallpox from the British Isles by use of quarantine and variolation. Jenner’s vaccine, of course, would offer a far safer alternative, and we’ll go into this in part 2, but widespread variolation directly led to vaccine development. In English North America, these ideas caught on easily — mandatory variolation was practiced in Boston, and when the colonies rebelled, George Washington ordered variolation of all his new recruits. All of this is to suggest that by the 1700s when Lord Amherst is considering biological warfare, the English were well-versed in how to spread the disease, and would have had supplies of dried scabs and pus on hand in order to practice variolation to protect their own people, as well as public smallpox hospitals that provided ample fresh material. It’s no coincidence that the people who understood management of smallpox on a population level the best — and would invent the mechanism to rid the world of it — would also be the first to plot to use smallpox as a weapon against populations. 


And indeed, there’s plenty of more documented occurrences of using smallpox as a weapon in the English world. During the American Revolutionary War,  the British attempted to foment smallpox outbreaks on the rebels lines, and during the follow up War of 1812, the Americans would repay the favor by trying to start outbreaks among British-aligned Indian tribes. During the American Civil War, there were widespread rumors in Confederate territory that the Union was attempting to spread smallpox in the south. While these we apparently baseless, we know for sure that the Confederacy attempted to use biological warfare against the North. Luke Pryor Blackburn, a physician from Kentucky, bought a large amount of blankets and clothing from yellow fever hospitals in Bermuda, and shipped a valise of smallpox-tainted clothing to President Lincoln. Unfortunately for Blackburn, we know today that yellow fever is spread by mosquitoes, not fomites, and Lincoln had actually been infected with a mild case of smallpox several years before, rendering him immune. A war criminal by modern conventions, his plot was revealed by one of his associates, and he escaped prosecution after the war in Canada, though he later returned to his native Kentucky where was elected governor post-Reconstruction. As the United States spread West across the continent, smallpox followed, and the stories increased of whites intentionally spreading the disease to natives.While the claims that the US army intentionally spread smallpox among the Mandans by disgraced historian Ward Churchill have been debunked, there are first hand accounts of wagon trains intentionally leaving behind smallpox-tainted clothes to attempt to spread the disease. 


These claims are hard to investigate, and the cataclysmic nature of epidemics lends itself to rumor. But it’s clear that the belief that whites were spreading smallpox through clothes was widespread in white, black, and Indian communities. The folklorist Adrienne Mayor has analyzed many of these stories and convincingly argued that they are examples of archetypal “poisoned dress” or “Nessus shirt” stories — named after the poisoned shirt given by his wife that killed Hercules. These stories have typically proliferated when populations are under external threats, and would have served as a warning against the white invaders, a way to contextualize these new outbreaks, and a way to define acceptable warfare. 


Though I’d also argue that it’s fully possible that the preponderance of these tales might also be because whites were intentionally spreading smallpox. I’ve mentioned multiple times that “evidence is lacking,” but there’s one other time that strong circumstantial evidence suggests that the British used smallpox with genocidal attempt again a native population, and that’s the conquest of Australia.


Let’s start with the undisputed facts. The British Empire used to ship convicts to its North American colonies, but after the treaty of Paris resulted in American independence in 1783, this was cut off. The remote southern continent of Australia made an attractive alternative option, and in 1787, the First Fleet set sail with between 1000 and 1500 convicts, marines, and seamen to set up a colony in Botany Bay. At this time, Australia was already populated by up to one million aborigines, located in the hospitable coastal regions. In 1789, a massive smallpox outbreak started in the area around Botany Bay that would ultimately killed up to 90% of the aborigines in that area, and devastate the population throughout the continent. The HMS Sirius was one of the ships to accompany the First Fleet, and returned to England soon after founding the colony. When she returned two years later, the crew was astonished at that had happened. A lieutenant Bradley wrote in his log that he was shocked at the small number of natives who greeted them at Sydney Cove. And Midshipman Newton Fowell would later write in his journal about all the bodies the crew would find. He saw them “laying dead on the beaches and in the caverns of rocks, forsaken by the rest as soon as the disease is discovered on them. They were generally found with the remains of a small fire on each side of them and some water left within their reach.” And the final undisputed facts: the First Fleet carried vials of smallpox, to be used for variolation in case the settlers encountered the disease on the new continent. And there was no smallpox among the First Fleet prior to landing — the Surgeon General kept precise records, and the 252 day journey was long enough that any existing disease would have burnt itself out. 


There are two competing theories about how smallpox was spread — but the dominant explanation among modern historians is that it came from the settlers, very likely deliberately. The historian Christopher Warren has pointed out the precarious position of the settlers. The First Fleet left without its military supplies — it had no extra supplies of ammunition, or tools to repair its weapons, and while they purchased musket balls in Rio de Janeiro, records show that they would have lasted less than a year. The amount of local resistance was much higher than expected — the British had stolen a considerable amount of their land, and fishing nets in the harbor quickly depleted traditional fisheries. The British had only 160 marines, and the governor of the new colony wrote that he would need at least 500 more to appropriately protect the colony. And so by 1789, the settlers would have viewed their new settlement on the verge of being overrun and collapsing. It is within this context that smallpox broke out among the aborigines. The disease was devastating — a case-fatality rate was estimated up to 70%, as tribes would scatter and disrupt the traditional methods of hunting and gathering. Any resistance to the British collapsed, allowing the colony breathing room to wait for resupply ships. Warren argues that the British had the appropriate knowledge, precedent, and the supplies of smallpox to carry off such an attack.


People at the time suspected the colonists of using smallpox as a weapon; we know because we have a letter from the  Captain of the Sirius who defended himself, writing, “It is true, that our surgeons had brought out variolous matter in bottles; but to infer that it was produced from this cause were a supposition so wild as to be unworthy of consideration.” He blamed, of course, the French for spreading the disease. But as alternative explanations have been winnowed down, future generations have found those bottles of smallpox scabs more and more worthy of consideration. But unless new documents are unearthed, this will remain circumstantial. 


So there you have it — at the same time that humanity was learning to contain smallpox, we turned it into a weapon to be used against our enemies, and as a tool for genocide. Next month, both this contradictory themes will be taken to its logical conclusion in the 20th century — while we discover how to prevent smallpox and the dream of eliminating the disease becomes a reality, we further weaponize the virus. And how humanity’s great success in destroying our greatest enemy potentially sets us up for an even scarier type of smallpox blanket.


Well, that’s it for the show. But wait! It’s time for #AdamAnswers! I got a lot of great questions this month, so I’ll be answering some next time. But given the subject of this episode, it’s apropros to answer Dr. David Serota’s question: “What is the most infectious disease?” So first let’s talk about the difference between diseases being infectious and contagious. Though these terms are used interchangably, they have small differences. A disease infectiousness refers to how many organisms it takes to cause the disease. So for example, salmonella isn’t particularly “infectious” by this standard — it takes ingestion of 100,000 organisms to cause the disease. Viruses or spores can cause disease with a single copy, making them far more infectious. Contagiousness refers to the ability of a disease to spread. However, I don’t want to be pedantic — most people, and that means most doctors too, use both these words to mean how easily a disease spreads.


So going back to my MPH days, in epidemic theory we have the basic reproductive rate, called R-naught; that’s R with a little zero by it. This refers to the ability of a single infected individual to cause a secondary infections in a susceptible population. A R0 of one will spread to one more individual — it’ll remain endemic. Less than 1 and it’ll burn out. Greater than one and it will cause an epidemic.


This is a theoretical construct, because a fully susceptible population doesn’t really exist. We have vaccination now, and modern methods to deal with outbreaks like quarantine and isolation. That being said, we’ve calculated R0s for basically every infectious organism. And the winner is …. Measles! WIth an R0 of 12-18, followed closely by pertussis with an R0 of 12-17. Smallpox comes in around fourth, with an R0 of 5 to 7. Let’s put this in perspective. Last year the world collectively freaked out about Ebola. To this day, I get asked by patients if I was exposed to ebola while I worked in Botswana (mind you, the US had more cases than Botswana — which had 0). You’d think it must be the most infectious disease in human history. But do you know what the R0 is? In West Africa, which lacks the sophisticated public health infrastructure of high income countries, It’s been calculated at 2-3. 


One final thing to mention — for the 7 most infectious diseases by R0, we have vaccinations for all of them. Vaccination has saved millions — arguably billions — of lives. The current attack on vaccination programs represents an attempt to undo probably the greatest life-saving intervention humanity has even undertaking.


OK, so I haven’t strictly been counting, but I think Dr. Serota deserves some sort of award for submitting the most questions to #AdamAnswers. We could rename it something like #DrSerotaAsks, but then we lose the alliteration. To the remainder of my listeners — beat Dr. Serota. Submit more questions! IF you have any question about medicine, no matter how trivial, silly, — or fundamentally deep — ask me on Twitter @AdamRodmanMD.


I hope you enjoyed the episode! I had originally planned to update my third episode, but like often happens I went down the rabbit hole, and you’re listening to the fallout. A couple updates — first, I made a short video about my time in Botswana for my job. If you’re curious what I was up to there, I posted it to the website, and you can see it on my Youtube channel. I’ll warn you right now; it’s really, REALLY cringe-worthy. 


And second, I’ve launched a Patreon account for the podcast. Bedside Rounds has grown dramatically since I was a resident looking for a good storytelling medical podcast. Each monthly episode takes up to 20 hours of research, writing, recording, and editing. Mind you, I love doing this, but it is my hobby — believe it or not, I’m a full time doctor on top of all my other extracurriculars. So if you love listening to Bedside Rounds as much as I love making it, consider giving some support — no matter any amount — at www.patreon.com/BedsideRounds


You can listen to all our episodes at www.bedside-rounds.org, on Apple podcasts, Stitcher, or the podcast retrieval method of your preference. I’m on facebook at /BedsideRounds and twitter @AdamRodmanMD, so drop by and say hi — now with 280 characters!


All of the sources are on the website.


And finally, while I am actually a doctor and I don’t just play one on the internet, this podcast is intended to be purely for entertainment and informational purposes, and should not be construed as medical advice. If you have any medical concerns, please see your primary care provider.