A Columbian exchange

A friend ponders:

Today I was reading some entries in The Oxford Companion to Archaeology. Among other things, I read about how the conquistadors were successful in part because the Aztecs and Maya were decimated by smallpox. The conquistadors unwittingly introduced smallpox into the indigenous populations, which had no resistance to the foreign pathogen. Fortuitous biowarfare. That, along with other factors (e.g. superior tactics and technology), enabled them to subdue these warrior civilizations, even though the conquistadors were vastly outnumbered by hostile natives.

This isn't the first time I've read that explanation. But I have some questions:

i) To begin with, why wouldn't that be a two-way street? If the conquistadors were carriers, for which the natives had no resistance–why weren't the natives carriers, for which the conquistadors had no resistance?

ii) According to the CDE, the incubation period for smallpox is between 7-17 days, during which an infected person is asymptomatic and not contagious.

So a sailor would have to become infected before he boarded a ship in Spain. And that would have to be during the incubation period, when he was still asymptomatic. I take it for granted that the captain and crew would not permit a sailor with smallpox symptoms to board the ship. So his symptoms would have to develop at sea, at which point he becomes contagious.

iii) We have to compare that with the time it took ships to sail from Europe to the Americas. Here are two estimates:

Since ships in the 1700s relied on sails to propel them, the length of the voyage greatly depended on the wind. An immigrant who made the journey in 1750 reported that it could take between eight and 12 weeks, while another who arrived in 1724 reported that the journey took six weeks and three days. The average journey was about seven weeks. (Source)

Henry Hudson was a European explorer traveling across the Atlantic during the colonial period. It took Hudson more than two months to sail from Amsterdam to New York City on his sailing ship, the Half Moon. (Source)

Assuming that's accurate, an infected sailor would become visibly symptomatic and contagious during the transatlantic passage. Assuming the crew didn't chuck him overboard, wouldn't there be a raging epidemic onboard by the time the ship docked in Mexico? But from what I've read, the conquistadors were asymptomatic when they disembarked. Moreover, I haven't read reports of conquistadors developing smallpox days or weeks after their arrival. Admittedly, my knowledge of the topic is quite cursory.

Just my thoughts:

I. A two way street

I agree it was a two way street. Native Americans (presumably including the Aztecs and Mayans) did likewise transmit diseases to Europeans (presumably including the conquistadors). For example, it's thought syphilis was likely transmitted from the New World to the Old World (on the Columbian theory). And before antibiotics syphillis could be quite harmful and sometimes even fatal.

There are other diseases Native Americans transmitted to Europeans, though I don't know if these were specifically from the Aztecs or Mayans (e.g. a species of hookworm; Chagas; Rocky Mountain Fever, though this was discovered much later than the 1500s).

II. Smallpox

Some facts about smallpox:

1. Smallpox is a very large and complex virus. An ancient virus, from the dawn of civilization.

2. Smallpox is thought to have originated from a domesticated animal, but it doesn't (or no longer can) infect any domesticated or any other animal. That is, there are no animal reservoirs which harbor smallpox. Smallpox only infects humans.

3. There are actually two main types of smallpox: major and minor. Historically, smallpox major has a high mortality rate (30%), while smallpox minor a much lower one (1%). We could actually subdivide further, but it's not really all that relevant.

   However, I don't know the answer to this, but I wonder if minor existed at this time, and if so, if being infected with minor and surviving grants immunity to major?

4. Smallpox is primarily transmitted either by droplets up to 3-6 feet (e.g. sneezing) or aerosols which travel farther than droplets and remain suspended in the air for longer periods of time (e.g. coughing). It's highly contagious, though there are other diseases which are more contagious.

   For example, if we compare by herd immunity, measles require upwards of 90-95% of a community to be vaccinated in order to keep measles from spreading to the unvaccinated in a community. However, with smallpox, about 80% of a community needs to be vaccinated in order to keep smallpox from spreading to the unvaccinated in a community. Still high, but not as high as measles.

5. The average incubation period for smallpox is 10-12 days (range is usually from 7-17 days). The course of smallpox can vary, but usually symptoms will subside 14 days after onset. But (assuming the person survives) it takes another 7-14 days for the scabs to fall off. A person is considered no longer contagious until all their scabs have fallen off. Say for example: 10 days incubation period + 14 days symptoms to subside + 14 days for scabs to fall off = 38 days.

   In case anyone would like a bit more detail (though I could go in more depth than even here). After the incubation period, the patient will experience an acute onset of general signs and symptoms lasting 2-3 days (e.g. fevers, chills, rigors, malaise, aches and pains, nausea and vomiting). After these 2-3 days, the patient will develop a centrifugally distributed rash with lesions usually involving the face and extremities. Over the next 7-8 days, these lesions typically generalize across the entire body, and evolve through various stages (i.e. macular, papular, vesicular, pustular). Within a month or so, the patient will have either improved or not, but even if they improve a lot of complications may persist (e.g. permanent scarring, blindness, arthritis, infection with other opportunistic pathogens like pneumonia).

6. Smallpox doesn't have a latent state. It doesn't hide as an asymptomatic infection. There's no carrier state for smallpox. Smallpox will produce overt signs (e.g. rash, lesions). (As an aside, this is one reason smallpox was able to be "eradicated".)

7. If a person is infected with smallpox, but doesn't die, instead recovers, then (generally speaking) they should have lifelong immunity.

8. As far as anyone is aware, smallpox has been "eradicated". I think the last known case was back in the 1970s. The only official specimens are in the CDC and I believe somewhere in Russia (though it's known the Soviet Union did attempt to weaponize smallpox in the past).

   Of course, who knows if terrorists or other nefarious groups have acquired smallpox which they could weaponize? After all, at one point, there were a lot of labs around the world which had smallpox since there was a lot of research on it. They should have destroyed all the smallpox in their possession, but did everyone do so?

III. Musings and speculations

Given all this:

1. I suppose the straightforward answer (or one straightforward answer) could be if the conquistadors had already been exposed to smallpox in Spain or Europe and survived, then traveled to the New World to infect the Native Americans.

2. People like Jared Diamond and Alfred Crosby talk about human contact with animals (especially domesticated animals) in the Old World vs. New World since animals can be reservoirs for infectious diseases. Specifically, living in close proximity to more varieties of animals might be relevant in building a more robust immune system among Europeans like the Spanish in contrast to Native Americans like the Aztecs and Mayans. However, it's debatable, I think.

   More to the point, since smallpox doesn't have an animal reservoir, since smallpox only infects humans, thus humans are its only reservoir, I'm not entirely sure how arguments from Diamond and Crosby would be relevant to smallpox, except indirectly at best, even if they are relevant to other communicable diseases?

3. I believe people like Diamond and Crosby also talk about how much more dense European population centers were at the time in comparison to Native American population centers, where only a city like Tenochtitlan would've rivaled Europe. A more dense population center may mean more likelihood of exposure to various pathogens, which in turn could perhaps account for more robust immune systems among Europeans in contrast to Native Americans. That might be worth exploring as well, but again it seems to me it's a debatable topic.

4. Generally speaking, it's possible the immune systems of Aztecs and Mayans are less genetically heterogeneous to one another than the immune systems of the Spanish to other Europeans. Perhaps especially if we accept the Bering strait theory that Native Americans trace their ancestry back to those groups which crossed the Bering strait.

   Anyway, if the Aztecs and Mayans have more genetically similar immune systems to other Native Americans than the Spanish do to other Europeans (say if the immune systems of all Native Americans are 50% identical, while the immune systems of all Europeans are 10% identical, just to use completely made-up figures), then it's possible a pathogen like smallpox could wreak havoc among Native Americans more easily if the pathogen can take advantage of something in the more similar immune systems, whereas the Spanish could more likely resist it.

   However, once again, I think this is debatable. It could just as well be entirely mistaken.

5. Another consideration is the climate and environment in which infectious diseases tend to thrive and spread. Say Mesoamerica vs. the Spanish peninsula. Was there anything about each environment that made it more likely for certain diseases to thrive and spread? Or which inhibited them from thriving and spreading? Or say temperate climates vs. tropical or sub-tropical climates? And so on.

6. Quite interestingly, historian Suzanne Alchon argues the following in her book A Pest in the Land: New World Epidemics in a Global Perspective (emphasis mine):

   This study of disease among the native peoples of the New World before and after 1492 challenges many widely held notions about encounters between European and native peoples. Whereas many late twentieth century scholars blamed the catastrophic decline of postconquest native populations on the introduction of previously unknown infections from the Old World, Alchon argues that the experiences of native peoples in the New World closely resembled those of other human populations. Exposure to lethal new infections resulted in rates of morbidity and mortality among native Americans comparable to those found among Old World populations.

   Why then did native American populations decline by 75 to 90 percent in the century following contact with Europeans? Why did these populations fail to recover, in contrast to those of Africa, Asia, and Europe? Alchon points to the practices of European colonialism. Warfare and slavery increased mortality, and forced migrations undermined social, political, and economic institutions.

   This timely study effectively overturns the notion of New World exceptionalism. By showing that native Americans were not uniquely affected by European diseases, Alchon also undercuts the stereotypical notion of the Americas as a new Eden, free of disease and violence until the intrusion of germ-laden, rapacious Europeans.

7. Along similar lines, it might be useful to look at, say, contemporary tribes in places like South America or Asia (e.g. Papua New Guinea) which have been isolated from contact by civilized societies. I presume anthropologists, for example, would take care to vaccinate themselves against known native diseases, so in the case of modern tribes it might not be a two way street like it was in the past. However, would anthropologists risk bringing their own diseases to some of these tribes if they make contact with these tribes? I suppose they take care to mitigate this possibility with good hygiene, minimal contact, etc. But still the possibility is there.

   Or if these isolated tribes happened upon people from their surrounding modern society. Suppose an Amazonian tribe happening upon Brazilians without any prior warning or other preparation by either side. Would there be any relevant parallels between something like this and the Columbian exchange of disease which we could learn from?

8. By the way, I suppose if liberal violent PETA types had their way, perhaps smallpox would now be on an endangered species list, and in fact they may even try to spread it! I hope this is just an overly active imagination on my part.

IV. "Genocide"

1. I've also read (mostly from liberals) how Europeans brought smallpox and other diseases to the New World, thereby causing a "genocide" among Native Americans. I think the term "genocide" is a highly loaded term, to say the least.

   For one thing, did all Europeans in general intentionally give diseases to Native Americans with the goal of wiping out an entire peoples or population? Wasn't the situation far more complex? At the bare minimum, we need to make distinctions between different Europeans and different Native Americans. Perhaps there were some Europeans who did so, but we can't generalize from some to all (e.g. there were some Europeans who helped some Native Americans get inoculated).

   Take this example. I've read there's some debate over some Englishmen giving blankets infected with smallpox to Native Americans in order to kill them. If true, then this would indeed have been a vile and reprehensible act, worthy of all condemnation. Regardless, let's assume it is true - can we therefore conclude all English colonials did the same to all Native Americans whom they encountered?

2. I've read some people argue as much as 90% of the New World population was destroyed thanks to disease brought by Europeans. Where does this figure come from? How is it calculated?

   For example, is it based on some epidemics (e.g. the cocoliztli epidemics), which, let us say, killed 90% of the Native Americans, then extrapolated to all other Native American communities or populations?

3. A couple of Mesoamerican epidemics in the 1500s, which killed millions, were caused by what the natives called "cocoliztli". There's debate over what cocoliztli was. Was it smallpox? Was it measles? Was it some unknown disease? Did it originate from the Old World or the New World?

   I've read some argue cocoliztli was a disease indigenous to the New World rather than transmitted by Europeans. For example, see here.

   I haven't deeply looked into any of this, so I don't know.

   However, if cocoliztli was indigenous to the Americas, then it would undercut the idea that it was the European diseases alone which were responsible for the alleged "genocide" of Native Americans. Especially if cocoliztli was not smallpox.

4. Likewise, from the same article:

   In the 1530s, a band of Spanish adventurers conquered the Inca Empire. It is commonly believed that some kind of epidemic devastated the Andes immediately prior to the Spanish arrival. Noble D Cook has advanced much evidence and argued strongly that this epidemic was of Old World origin, perhaps measles combined with pneumonic plague and influenza.46 However, if our hypothesis for the Mexican case - that some pre-existing New World viral disease became epidemic due to ecological changes brought about by large-scale and relatively sudden alterations of human agricultural practices - is valid, then perhaps the Peruvian case merits further study along these lines.

5. Perhaps one reason smallpox so easily spread across Mesoamerica (and other parts of the New World) was due to the collapse of social order among the Aztecs and Mayans? I presume the Aztecs and Mayans faced disease epidemics in the past since most civilizations seem to have. If so, they would've presumably been better able to isolate and stem epidemics. Like leaders to take charge and organize, quarantine the infected, etc.

6. I've read some Native American populations didn't suffer as badly from some Old World diseases as Europeans did (e.g. the Quechua people in the Andes Mountains and malaria, due to their consuming tea from leaves containing quinine, which helps mitigate malaria). Point being, it seems more complex than simply saying, all Native Americans suffered from disease at the hands of Europeans.

7. Of course, it's not only the Europeans who brought disease. For example, it's possible African slaves brought yellow fever to the New World. Although, if true, no doubt some would still like to blame Europeans for bringing the slaves. But that would be overly simplistic to do.

8. Speaking of which, since the Europeans were planting colonies all around the world at this time, there were a lot of communicable diseases between Europe, Africa, and Asia too. Many which killed scores of people in Africa and Asia (e.g. re-occurences of the black death in northern Africa). I wonder if any of them were as catastrophic as what happened to Native Americans?