Jared Diamond considered the disastrous impact of Eurasian and African diseases on the inhabitants of the New World, contrasted with a much smaller impact in the opposite direction, and concluded that a major factor had probably been transmission from domesticated animals. Eurasians domesticated quite a few animals, Amerindians not many – perhaps that was the explanation. In Guns, Germs, and Steel (p 207), he mentions measles, tuberculosis, smallpox, influenza, pertussis (whooping cough), and falciparum malaria as likely cases of transmission from domesticated animals.
We know a lot more about this we did twenty years ago, since we’ve been sequencing the genes of everything in sight – and it appears that Diamond was mistaken about the most important members of that list. TB appears to be ancient in humans, smallpox probably came from some East African rodent, while falciparum malaria seems to have derived from a form of malaria carried by gorillas. Measles really does descend from rinderpest, a cattle plague, but then rinderpest (and mumps) probably descend from bat viruses. Domesticated animals do play a role in influenza, along with wild birds. I don’t think we know the origins of pertussis.
So why then was the Old World such a fount of infectious disease? Well, it’s bigger. Civilization was older, had had more time to pick up crowd diseases. Important pathogens, especially those with insect vectors like malaria, maybe couldn’t make it through Beringia. Transportation and trade were more advanced in the Old World, and spread disease more efficiently.
I don’t think that Diamond was making excuses for Amerindians in this, as he was when talking about domestication itself: having lots of plagues isn’t usually considered an accomplishment. It seemed like a reasonable idea at the time, considering the state of the art. It seemed so to others as well, like William McNeill. It’s not totally wrong – definitely true for measles – but it’s not a huge part of the explanation.
West Hunter 
RE: New World epidemics,
Here’s an interesting one: The Cocoliztli Epidemic of 1576
“The cocoliztli epidemic of 1576 refers to millions of deaths in the territory of New Spain in present-day Mexico in 16th century attributed to one or more illnesses collectively called cocoliztli.
The cause of the epidemic remains unknown though it might have been an indigenous viral hemorrhagic fever, perhaps exacerbated by the worst droughts to affect that region in 500 years and living conditions for indigenous peoples of Mexico in the wake of European invasion.[1] Some historians have suggested it was typhus, measles, or smallpox, though the symptoms did not match.”
“Cocoliztli epidemics usually occurred within two years of a major drought while another disease called “matlazahuatl” had appeared within two years of the rainy season.The epidemic in 1576 happened after a drought stretching from Venezuela to Canada.[5][6] The correlation between the drought and the disease seems to be that in the rains that followed the drought, populations of the Vesper mouse, a carrier of viral hemorrhagic fever, increased as conditions improved.[4] There have been 12 epidemics since thought to be of cocoliztli, with the largest being in 1545, 1576, 1736, and 1813″
https://en.wikipedia.org/wiki/1576_Cocoliztli_epidemic
Wow, if the chart on Wikipedia is right, the 1545 and 1576 Cocoliztli epidemics were twice as important as Smallpox as drivers of an almost total population collapse in Mexico — from 22 million down to 1.5 million in around 80 years! I’m kind of astonished, especially as I’ve never even heard of the disease before now.
I’ve never heard of it either. One thing strikes me: presumably this disease would hit the Spaniards and their African slaves hard too.
But there is no mention of it by contemporaries.
Some diseases that came from Africa (like yellow fever) hit both Europeans and Amerindians hard. That was documented.
The books I’ve read are more about history than the science of disease.
But there are extensive contemporary writings about the new world. Seems odd that this is not mentioned.
“I’ve never heard of it either”
It is strangely obscure; I first learned of it a couple of years ago when I was talking to a colleague who specializes in the history of colonial Mexico.
“But there is no mention of it by contemporaries.”
Here are some contemporaneous accounts:
” Friar Juan de Torquemada, a Franciscan historian writing in 1577, described the wake of cocolitzli in typical detail:
“It was a thing of great bewilderment to see the people die. Many were dead and others almost dead, and nobody had the health or strength to help the diseased or bury the dead. In the cities and large towns, big ditches were dug, and from morning to sunset the priests did nothing else but carry the dead bodies and throw them into the ditches. . . . It lasted for one and a half years, and with great excess in the number of deaths. After the murderous epidemic, the Viceroy Martin Enriquez wanted to know the number of missing people in New Spain. After searching in towns and neighborhoods it was found that the number of deaths was more than two millions.””
“To prove anything beyond a hunch, Acuna-Soto knew he would need good forensic science. He considers himself fortunate to have found the work of Francisco Hernandez.
Hernandez, personal physician to Philip II of Spain, was named Proto-Médico de su magestad de todas las Indias in 1576. He was, in effect, the surgeon general of New Spain.”
“Philip sent him to Mexico to see what he could learn of native medicines,” says Acuña-Soto. “Hernandez learned five Indian languages and wrote 50 volumes based on his own observations and interviews with hundreds of Indians. He performed autopsies on many of the victims of the 1576 epidemic. But the books arrived back in Spain just after Philip II’s death. Philip III considered the project too expensive to publish, and the manuscript disappeared for 400 years. Around 1950 it resurfaced in the Hacienda Library in Madrid.”
Six years later, Mexican physician German Somolinos d’Ardois published an account of that manuscript. Although Hernandez’s descriptions of what he saw were rendered in an unsophisticated Latin, Somolinos d’Ardois was able to conclude that Hernandez considered the 1576 epidemic different from those that had come earlier.
Acuña-Soto sent the text of the original Latin manuscript to a friend, a physician working with the Centers for Disease Control in Washington, D.C., who was also a Greek and Latin scholar. The new translation he got back described cocolitzli in terms that did not match any Old World disease:
The fevers were contagious, burning, and continuous, all of them pestilential, in most part lethal. The tongue was dry and black. Enormous thirst. Urine of the colors of sea-green, vegetal green, and black, sometimes passing from the greenish color to the pale. Pulse was frequent, fast, small, and weak—sometimes even null. The eyes and the whole body were yellow. This stage was followed by delirium and seizures. Then, hard and painful nodules appeared behind one or both ears along with heartache, chest pain, abdominal pain, tremor, great anxiety, and dysentery. The blood that flowed when cutting a vein had a green color or was very pale, dry, and without serosity. . . . Blood flowed from the ears and in many cases blood truly gushed from the nose. . . . This epidemic attacked mainly young people and seldom the elder ones.”
http://discovermagazine.com/2006/feb/megadeath-in-mexico
Thanks for the info. None of the books I read mentioned it under that name. Maybe it had different names in different places. It sounds awful.
But were the Europeans susceptible too? If they were then it’s a good bet was in the Americas before Columbus.
A recent study suggests that it might have been an Old World disease:
“In an attempt to settle the question, a team led by evolutionary geneticist Johannes Krause at the Max Planck Institute for the Science of Human History in Jena, Germany, extracted and sequenced DNA from the teeth of 29 people buried in the Oaxacan highlands of southern Mexico. All but five were linked to a cocoliztli that researchers think ran from 1545 to 1550.
Ancient bacterial DNA recovered from several of the people matched that of Salmonella, based on comparisons with a database of more than 2,700 modern bacterial genomes.
Further sequencing of short, damaged DNA fragments from the remains allowed the team to reconstruct two genomes of a Salmonella enterica strain known as Paratyphi C. Today, this bacterium causes enteric fever, a typhus-like illness, that occurs mostly in developing countries. If left untreated, it kills 10–15% of infected people.”
“A team led by Mark Achtman, a microbiologist at the University of Warwick in Coventry, UK, collected and sequenced the genome of the bacterial strain from the remains of a young woman buried around 1200 in a cemetery in Trondheim, Norway. It is the earliest evidence for the now-rare Salmonella strain, and proof that it was circulating in Europe, according to the study.”
“The existence of Salmonella Paratyphi C in Norway 300 years before it appeared in Mexico doesn’t prove that Europeans spread enteric fever to native Mexicans, says Schroeder, but that hypothesis is reasonable. A small percentage of people infected with Salmonella Paratyphi C carry the bacterium without falling ill, so apparently healthy Spaniards could have infected Mexicans who lacked natural resistance.”
https://www.scientificamerican.com/article/collapse-of-aztec-society-linked-to-catastrophic-salmonella-outbreak/
An earlier episode of smallpox could also have provided (or helped provide) these conditions
Any relation to the other Torquemada?
“The epidemic in 1576 happened after a drought stretching from Venezuela to Canada.”
Climate change! Stop driving cars immediately!
More info on cocoliztli:
“The native population collapse in 16th century Mexico was a demographic catastrophe with one of the highest death rates in history. Recently developed tree-ring evidence has allowed the levels of precipitation to be reconstructed for north central Mexico, adding to the growing body of epidemiologic evidence and indicating that the 1545 and 1576 epidemics of cocoliztli (Nahuatl for “pest”) were indigenous hemorrhagic fevers transmitted by rodent hosts and aggravated by extreme drought conditions.”
“The native people of Mexico experienced an epidemic disease in the wake of European conquest (Figure 1), beginning with the smallpox epidemic of 1519 to 1520 when 5 million to 8 million people perished. The catastrophic epidemics that began in 1545 and 1576 subsequently killed an additional 7 million to 17 million people in the highlands of Mexico (1–3). Recent epidemiologic research suggests that the events in 1545 and 1576, associated with a high death rate and referred to as cocoliztli (Nahuatl for “pest”), may have been due to indigenous hemorrhagic fevers (4,5). Tree-ring evidence, allowing reconstructions of the levels precipitation, indicate that the worst drought to afflict North America in the past 500 years also occurred in the mid-16th century, when severe drought extended at times from Mexico to the boreal forest and from the Pacific to Atlantic coasts (6). These droughts appear to have interacted with ecologic and sociologic conditions, magnifying the human impact of infectious disease in 16th-century Mexico.”
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2730237/
Following drought? maybe some variant of hantavirus.
As to the notion that cattle are a special vector… American bison and domestic cattle freely interbreed and produce fertile offspring (in fact nowadays few wild bison are entirely free of cattle genes) — so seems to me that shouldn’t have been significantly different in America — exposure levels may even have been higher, considering that bison were all over North America (tho shrinking due to overhunting by the Indians), but in concurrent Europe, cattle were mostly a rich man’s herd.
“but in concurrent Europe, cattle were mostly a rich man’s herd.” Where do these batty notions come from? If the peasant doesn’t have a cow he doesn’t have milk or cheese. If he doesn’t have cheese he struggles to survive the winter.
Ever heard of sheep or goats? those are the poor man’s herd for milk and cheese (not to mention meat and fiber). They don’t require NEARLY as much fodder to survive the winter, meaning you don’t need other peasants to cut hay for you.
But the peasant did herd a cow or two. Else why give the commoner the right to graze his cattle on the commons?
http://www.theprairiehomestead.com/2010/11/goat-101-cow-vs-goat.html
Some speculations on population decline in Mexico:
Coe, Snow and Benson, Atlas of Ancient America (1986)
Mexico: Original population of 11M to 25M (“lower figure commands more support”) fell to 1.25M (1625)
Massimo Livi-Bacci, Concise History of World Population History 2d (1996)
Mexico: Population fell from 6.3M (1548) to 1.9M (1580) to 1M (1605)
Skidmore & Smith, Modern Latin America (1997)
Mexico: Population fell from 25M (1519) to 16.8M (1523) to 1.9M (1580) to 1M (1605)
Stannard, American Holocaust (1992):
Mexico
Central: Population fell from 25.0M (1519) to 1.3M (1595)
SE: fell from 1,700,000 to 240,000
North: fell from 2,500,000 to 320,000
25 million seems to be favored nowadays for the pre-Conquest High…..But one should bear in mind Coe and Benson’s estimate of 11 to 25 million, with the “lower figure command[ing] more support”
Standard is calling it genocide, implying it was deliberate. From the Amazon description
That seems a bit much.
I understand the Black Death came to Europe as a side effect of Mongols invading to the east of Europe. But I wouldn’t go so far as to blame the Mongols of planning and executing it deliberately.
At least, I personally haven’t seen that. But I’m just an amateur historian.
That name is Stannard, not Standard.
The chap has a book to sell: “holocaust” presumably sells books.
The reader reviews are full of people writing: “We must admit this, no matter how painful and deal with it”.
More junk history: there’s a big market it for it. Stannard’s book is likely required reading for various history courses in the universities.
“More junk history: there’s a big market it for it. Stannard’s book is likely required reading for various history courses in the universities.”
I had to read chunks of it in grad school; it’s pure agit-prop.
A New Clue to the Mystery Disease That Once Killed Most of Mexico
https://www.theatlantic.com/science/archive/2018/01/salmonella-cocoliztli-mexico/550310/
“Now, DNA from 16th-century cocolitzli victims has offered up a somewhat unexpected new candidate: Salmonella enterica, or the bacteria that causes paratyphoid fever. The DNA evidence comes from the teeth of 11 people buried in a large Mixtec cemetery in southern Mexico.”
If recent transmission of virulent forms from domesticated animals is probably not important for most diseases of the Holocene, then should we largely retire the idea of pastoralist disease resistance?
The idea whereby pastoral cultures>number of domesticated animal interactions>diseases emerge first among pastoralists->pastoralists adapt and gain resistance earlier / more quickly (and in some iterations, whereby pastoralists are overall genetically healthier, more attractive and so on from this effect).
Often seems a flourishing meme in the comments on the ‘sphere that loosely exists around GNXP and this site, but does it have much reality from what we know about how these diseases actually arose?
Mongols were known to be highly susceptible to smallpox: http://scholars-stage.blogspot.com/2014/03/smallpox-on-steppe.html
Since many infectious diseases seem historically to have originated or become endemic in densely populated cities, one would expect people who are usually far away from those cities to have little defenses against these diseases. Many pastoralists therefore may have been at a disadvantage relative to some settled peoples.
This is also a theory about New World populations’ sensitivity to Old World diseases. They had been isolated for 10,000 years. I used a lot of Jared Diamond’s work in writing early chapters of my history of medicine that I wrote in the late 90s.
The important take away is that pastoralists are our natural superiors. Better just to bow to the Khan.
Somewhere long ago I read a conjecture that many of the diseases of Eurasia arose in China because that was the place where humans, fowls, and pigs lived hugger-mugger at high population density.
Not precisely conjecture. When you keep pigs and ducks together, as is common in rural China, coronaviruses native to pigs can get passed through ducks where they are altered sufficiently to become human-infective, and that’s why we regularly get “swine flu” from Asia. Basically it’s vaccine production in reverse.
Good thing the ferret never became a popular pet.
Interesting, Reziac. Are there any other diseases that can be attributed to pigs/ducks/humans?
I don’t know offhand, but canine parvovirus was suspected as starting life as feline panleukopenia (and one strain of parvo can infect cats), tho it could also have come from bovine parvovirus or human bocavirus. Far as I know we don’t have any original samples to examine (from when the disease was new in dogs); did it pass through birds? we don’t know, but it could have.
Viruses are both unstable and adaptable, so any change of environment can generate a new virus with potential new target species. Consider too that our own DNA is basically “accumulated virus cruft” … which may contribute to our immunity to the continuous seethe of viruses all around us.
Side note: distemper in dogs can be reliably treated with antibodies generated by Newcastle vaccine (which is for chickens), or in a pinch, with Newcastle vaccine itself.
http://www.edbond.com/antidistemper.html
And I can attest from experience that it works.
http://dispatchesfromturtleisland.blogspot.com/2017/02/smallpox-did-more-to-wipe-out-native.html
“One of the worst epidemics in human history, a sixteenth-century pestilence that devastated Mexico’s native population, may have been caused by a deadly form of salmonella from Europe, a pair of studies suggest.
In one study, researchers say they have recovered DNA of the stomach bacterium from burials in Mexico linked to a 1540s epidemic that killed up to 80% of the country’s native inhabitants. The team reports its findings in a preprint posted on the bioRxiv server on February 8. . . .
In 1519, when forces led by Spanish conquistador Hernando Cortés arrived in Mexico, the native population was estimated at about 25 million. A century later, after a Spanish victory and a series of epidemics, numbers had plunged to around 1 million. The largest of these disease outbreaks were known as cocoliztli (from the word for ‘pestilence’ in Nahuatl, the Aztec language). Two major cocoliztli, beginning in 1545 and 1576, killed an estimated 7 million to 18 million people living in Mexico’s highland regions.
“In the cities and large towns, big ditches were dug, and from morning to sunset the priests did nothing else but carry the dead bodies and throw them into the ditches,” noted a Franciscan historian who witnessed the 1576 outbreak.
There has been little consensus on the cause of cocoliztli—although measles, smallpox and typhus have all been mooted. In 2002, researchers at the National Autonomous University of Mexico (UNAM) in Mexico City proposed that a viral haemorrhagic fever, exacerbated by a catastrophic drought, was behind the carnage. They compared the magnitude of the 1545 outbreak to that of the Black Death in fourteenth-century Europe.
In an attempt to settle the question, a team led by evolutionary geneticist Johannes Krause at the Max Planck Institute for the Science of Human History in Jena, Germany, extracted and sequenced DNA from the teeth of 29 people buried in the Oaxacan highlands of southern Mexico. All but five were linked to a cocoliztli that researchers think ran from 1545 to 1550.
Ancient bacterial DNA recovered from several of the people matched that of Salmonella, . . . Further sequencing of short, damaged DNA fragments from the remains allowed the team to reconstruct two genomes of a Salmonella enterica strain known as Paratyphi C. Today, this bacterium causes enteric fever, a typhus-like illness, that occurs mostly in developing countries. If left untreated, it kills 10–15% of infected people. . . .
Krause and his colleagues’ proposal is helped by another study posted on bioRxiv . . . which raises the possibility that Salmonella Paratyphi C arrived in Mexico from Europe. A team . . . collected and sequenced the genome of the bacterial strain from the remains of a young woman buried around 1200 in a cemetery in Trondheim, Norway. It is the earliest evidence for the now-rare Salmonella strain, and proof that it was circulating in Europe . . .
The existence of Salmonella Paratyphi C in Norway 300 years before it appeared in Mexico doesn’t prove that Europeans spread enteric fever to native Mexicans, says Schroeder, but that hypothesis is reasonable. A small percentage of people infected with Salmonella Paratyphi C carry the bacterium without falling ill, so apparently healthy Spaniards could have infected Mexicans who lacked natural resistance. Paratyphi C is transmitted through faecal material, and a collapse of social order during the Spanish conquest might have led to the poor sanitary conditions that are ripe for Salmonella spread, Krause and his team note in the paper.”
Here’s a link to the Scientific American article on cocoliztli :
https://www.scientificamerican.com/article/collapse-of-aztec-society-linked-to-catastrophic-salmonella-outbreak/?WT.mc_id=SA_FB_HLTH_NEWS
Regarding fatal transmission, did syphilis come from the New World? Tabacco comes from the US doesn’t it?
Yes, syphilis came from the New World.
It is certainly plausible that, along with ideas, diseases also more spread easily in Eurasia than the Americas just due to geography.
Another one that affected Amerindians badly was leprosy. It seems to have arrived a lot later and to have come from the east. There are accounts of the terrible effects it had in Hawaii.
I’ve read (can’t remember where) that a large percentage of Eurasians are immune to it somehow. It spread like wildfire in Hawaii.
The Hawaiians aren’t Amerindians.
Yes, you’re right, I’m wrong. They were Polynesians.
But I seem to recall that they were more susceptible than Europeans to some diseases.
Not sure if was as bad as for the Amerindians.
The Hawaii crisis was dealt with by building a remote outpost in Hawaii and banishing sufferers. Missionaries were prepared to go there and one of them died of leprosy.
This was on the instructions of the native leaders who were terrified (understandably).
So that stopped the spread to the mainland. I read a whole book about it. It is now treatable.
The experience of Maori and other Polynesians is actually pretty important in this question in setting how important the Beringian filter Greg talks about (“Important pathogens, especially those with insect vectors like malaria, maybe couldn’t make it through Beringia.”). At least for the initial wipeouts.
Austronesian side ancestry of Polynesians probably diverge from Chinese at around 8,000 BC (early in agriculture), much later than the Chinese-like side of Amerinds (16,000 BC or earlier). But could be as late as 4000 BC. Expansion out of Taiwan probably hits around 4000 BC. Admixture with Melanesians happens around 3000 BC.
So the population diverges later, doesn’t go through the Beringian bottleneck, has their genetic diversity topped up with admixture from Melanesians.
But they still get hit by Eurasian diseases pretty bad. >50% reduction in population size for Maoris as I remember.
RE: Maori population decline:
“New Zealand (1800s):
Mark Cocker, Rivers of Blood, Rivers of Gold (1998)
Maori pop: 240,000 (pre-contact) to 40,000 (1896)
Clodfelter, Maori War (1860-72)
UK, NZ: 700 k.
Maori: 2,000”
So, around 200,000 deaths, with the vast majority of the deaths occurring because of factors like disease and hardship, not direct violence.
“New Zealand (1800s):
Mark Cocker, Rivers of Blood, Rivers of Gold (1998)
Maori pop: 240,000 (pre-contact) to 40,000 (1896)
Clodfelter, Maori War (1860-72)
UK, NZ: 700 k.
Maori: 2,000”
Should note that Cocker is a “high-counter” when it comes to pre-Contact population estimates for New Zealand. Other sources estimate the pre-Contact Maori pop. at approx 100,000. Using that as a base, the die-off would be around 60,000.
They were susceptible to smallpox. From a review of the book
I am curious why African diseases did not wipe Europeans the same way European diseases wiped Amerindians.
Mainly, latitude.
Most of them, dont do well beyond the tropics.
Europeans traveling to inland sub-Saharan Africa did poorly. I have read several accounts that describe about 90% dead on a trip of any length.
But there weren’t as many SSA’s in the Americas. And the parasites had to find suitable mosquitoes in the new world (yellow fever and falciparum malaria were the two big ones.)
And Europeans did die at fairly high rates where these two diseases became common. The suitable mosquitoes like the tropics, and never became permanently established in colder places. Read an account of the French attempt to build the Panama Canal. The fatality rate was pretty bad and this in part doomed their attempt.
Yellow fever was not permanently established in New Orleans but occurred in sporadic outbreaks over the years. People were terrified of it.
Rumours about the diseases spread around Europe and ships sailing to the fever areas had trouble finding crews.
And not all natives were killed by imported diseases. Some did survive. The same would apply to Europeans and the African diseases: some did survive.
I read once that the death rate among the crews of slavers was nearly as high as the rates for the slaves. West Africa was called “the white man’s grave”.
According to Philip Curtin, the mortality rate of early British colonial administrators in The Gambia in the 18th century exceeded 80%. This sample was rather small, and the figure was computed largely on a limited number of expeditions. By the way,
The choice of colonial outposts by the British in this part of West Africa in retrospect was crazy. For instance, the main British outpost in The Gambia was the island of Bathurst (which is now the capital and has been renamed as Banjul). It was, and to some extent it still is, a mosquito infested swamp. Another colonial outpost in the interior (about 150km from the Atlantic coast) of this colony was an island in the middle of River Gambia. It was, and still is, a mosquito infested swamp village. No wonder their mortality rate was so damn high in that part of the world.
I just read McCollough’s book on the Panama Canal. The accounts of mosquito control that Gorgas put into effect are interesting. Walter Reed had died of appendicitis in 1902 so Gorgas took over.
That’s the book I read too. During the French attempt, the causes of yellow fever and malaria were unknown. I remember the author explaining how the legs of beds were put in small containers full of water. This was to stop creepy crawlies from getting onto the bed.
Unfortunately, this was exactly the setup that the yellow fever mosquitoes really, really like: still and clean water.
By the time the Americans started it was known about the mosquitoes. A huge campaign to get rid of standing water or to cover it was put in place. It largely worked.
This other book, “Mosquito Empire” is a great resource for how disease determined winners and losers in the Caribbean and adjoining area.
It’s well written and all sources are noted. It’s far more professional than GGS.
Yes, the best breeding water for mosquitoes are small pools of still water with no fish in them to eat the mosquito eggs or larvae.
Maybe pertussis comes from dogs?
Dogs suffer from kennel cough, which is caused by Bordetella broncheiseptica. Apparently, this organism is quite close to Bordetella pertussis. No reason to think this, but it’s a thought.
Whooping cough’s origins are unclear, but it seems recent. There’s documents back to the late 12th century describing a “violent cough”…but people cough from colds. Other herbalist and apothecarist books don’t describe any conditions reminiscent of modern whooping cough.
Remember, whooping cough isn’t a disease that hangs around a population at a low, unobtrusive level. You get epidemics (and epidemics make it into history books). The first documented epidemic was in Paris, in 1578 (Guillaume de Baillou), well after the Columbian expansion. To be fair, pertussis does seem to have been well known by that point. But where are all the outbreaks?
It doesn’t seem to have existed before the medieval period – perhaps until the late medieval period.
Likely the other way around. Bordatella wasn’t commonly seen in dogs until about 30 years ago. Before that most “kennel cough” was caused by canine parainfluenza virus.
I’m very surprised no one knew of the basic disease ecology of the New World.
For an infectious disease, the typical response is that either the disease kills the host, which in turn will usually kill the disease organisms, too, or the host’s immune system kills the disease. So how can infectious diseases persist?
A) The disease organism finds a way of hiding from the immune system. TB does this, and so do retroviruses that incorporate themselves into the host’s DNA and remain quiescent most of the time.
B) The infectious organism can exist outside the host. Cholera in the tropics is a good example. The bacillus can exist in ground water, if the temperature is warm enough. Anthrax spores are another instance.
C) Rapid mutation. Flu strains keep shifting their antigens, so the immune system isn’t ready to attack the latest strain.
D) KEEP MOVING! This is the basic measles/smallpox strategy. If there are enough people in close contact, there will always be some people around to infect that never had the disease, and thus aren’t immune.
It’s that last that is the most important. With a large enough population (for these purposes, animal hosts are included in the population), a disease once introduced circulates forever. Without a large enough population in close contact, the disease runs out of hosts and disappears.
Measles in the British Isles are an excellent example. There are many small islands with inhabitants besides Britain and Ireland. Said islands used to be measles-free for decades at a stretch, then a case would be introduced, and in a short time almost everyone who had never had it would be infected. Then the disease would disappear again.
Meanwhile, in areas with around half a million people in reasonably close contact, such London, there would always be never-infected children available to catch it.
Now, apply this to the New World in the early days of human influx. One member of a group of hunter-gatherers may have picked up measles or flu as the band migrated out of Asia. The whole band might get it. But unless hunter-gatherer bands are quite thick on the ground, the disease organism runs out of new hosts and dies off.
For thousands to tens of thousands of years, the population wasn’t large enough for disease to be endemic. Eventually, population size and density got high enough fo endemic diseases. But the organisms weren’t there to take root. Finally, Europeans arrive, and the pandemics begin. The mass deaths damped out the transmission of most of them, periodically. Alas for the Amerinds, the Europeans kept arriving, and re-introducing diseases. Eventually, extreme selection pressure toughened up the indigenes.
So it goes.