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Public Radio's Environmental News Magazine (follow us on Google News)

Native Virus

Air Date: Week of

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It's long been assumed that Europeans were the bearers of the massive plagues that devastated Mexico in the 16th century. But now some scientists say the diseases may have been native to Mexico. And as Ingrid Lobet reports, drought, not colonialists, may have been the crucial factor in their spread.


CURWOOD: Spanish ships first set anchor off the coast of Mexico in 1519. A hundred years later, nine out of every ten native Mexicans was dead, mostly from disease. Smallpox germs from Europe were responsible for the first colonial plague in Mexico, in 1520. But now, some scientists say there were two subsequent epidemics that may have been caused by viruses native to the region. And those diseases may have been brought on by extreme drought. Ingrid Lobet has our report.


LOBET: Although Dr. Rodolfo Acu–a Soto is an epidemiologist, often you'll find him in a Catholic church, the guardian of so much of Mexico's past. He's a student of his country's rich history of plague, trying to understand what might happen in future epidemics. Here, and not for the first time, he talks a priest into opening a dusty archive.

[talking in Spanish]

LOBET: From a back room at the main cathedral in Oaxaca, a young cleric brings out a leather-bound city record dating to the late 1700s. It's a foot and a half high and three inches thick.

[talking in Spanish]

TRANSLATOR: Gorgeous, look at these letters scripted in gold. Pure cellulose paper, imported from Spain. And how much must this weigh, 11 pounds?

LOBET: The records paint a vivid picture of death in colonial Mexico. Here, Acu–a reads from an old municipal burial record.

[talking in Spanish]

TRANSLATOR: Fever, tuberculosis, chicken pox, gastroenteritis, enteritis, enterocolitis.

LOBET: No one, it seems, died of old age.

TRANSLATOR: Infant seizure, pneumonia, fever, pneumonia, typhoid fever, cholera, diarrhea, diarrhea, cholera.

LOBET: Even though the sweeping plagues happened centuries ago, they're well- documented. One reason is providence. It turns out, King Philip of Spain sent his personal physician to the New World just as the Great Plague of 1576 was sweeping Mexico. So Dr. Hernandez, the King's doctor, perhaps the best-trained western physician in the world at the time, witnessed the epidemic. He was examining patients, performing autopsies, and making notes about a plague so violent it would still be in the history books 400 years later. Yet, these notes lay forgotten until Dr. Acu–a and another research team stumbled upon them.

ACUNA: The descriptions are horrendous. It started with fever, chills, and in four or five days, they died. They bled through the noses, ears, mouth, everywhere. They become jaundiced, yellow. And also, they have these kind of ulcers in the lips and the genitals. They become mad, kind of insane, absolutely. And they were very anxious. And, enormous thirst.

LOBET: Dr. John Marr is a New York epidemiologist. He and his partner, Dr. Barry Kiracofe, an architectural historian, have been looking at this same 16th century record of the King's physician, as well as even older native accounts of epidemics in the Americas. Dr. Marr agrees it's clear that the common belief that Mexican Indians were killed off by smallpox is not scientifically viable.

MARR: So it was clear to me, at least, because Dr. Kiracofe had collected a number of primary resource papers, written by Spaniards, that the signs and symptoms of this disease that killed so many Aztecs included bleeding from the eyes, the ears, the nose, the mouth, vaginal bleeding, bleeding from the stomach, bleeding into the urine, bleeding under the skin, and a fulminant, rapid death within three or four days.

LOBET: Marr and Acu–a say modern medicine recognizes these symptoms. They are characteristic of a class that includes Ebola Fever, Rocky Mountain Spotted Fever, and certain kinds of Dengue-- a class Americans have been hearing more about recently--hemorrhagic fevers.

MARR: I would say, unequivocally, I fortunately had some guidance from some of the experts at the CDC. I talked with many people who are expert virologists and epidemiologists, and I think they would all conclude that it was a hemorrhagic fever.

LOBET: But what that disease was, whether it was transmitted by insect or mammal and under what conditions are still open questions. One hypothesis is tied closely to draught, a calamitous draught, stretching across North and Central America, one far worse than the Oklahoma dust bowl.


LOBET: A team of researchers is working in the forests of Oaxaca's Sierra Madre mountains, taking core samples out of the oldest trees, mapping that famous draught, the 16th century mega-drought, in detail. Because of its perch on the Pacific, Mexico has felt the cutting edge of Earth's changing weather patterns throughout the centuries.


CLEVELAND: Whoa. Beautiful. This is a nice tree. Oooh, lovely. Okay. Sometimes, getting it started is the hardest thing, which is why I use this starter.

LOBET: Malcolm Cleveland and Matthew Terrell are tree ring researchers, or dendrochronologists, from the University of Arkansas. Cleveland crouches beside a Douglas Fir.

CLEVELAND: Probably 250, 300 years old.

LOBET: The cores are pencil thin. They say it doesn't harm the tree at all.

CLEVELAND: Break the core off.

LOBET: Terrell explains Douglas Fir is famous for its ability to reliably put on new wood every year, wood that varies in thickness with rainfall.

TERRELL: Douglas Fir is like the holy grail for dendrochronologists, not only because it has an incredibly extensive range, but it has a very good climate signal almost everywhere you find it.

LOBET: Using the core samples and slices of downed trees, the University of Arkansas team, together with Mexican foresters, have painted the first real climate history of Mexico, including a map of the mega-drought. Epiphany can come when unlike spheres collide. Epidemiologist Dr. Acu–a Soto just happened to be in the audience when the Arkansas researchers presented their climate charts at a conference. He saw that there were two tall tent poles of peak drought in Mexico just at the same time as the two most notorious 16th century plagues.

ACUNA: A very, very interesting pattern appeared. Very severe, long drought, and then suddenly within the drought is a period of rain, exactly that of the time the epidemic appears.

LOBET: Dr. Acu–a and the Arkansas team began collaborating and developed a hypothesis that involves drought, brief rain, and disease carrying rodents.

ACUNA: If water becomes scarce in the countryside, rats and, in general, all the rodents get kind of clustered around the very scarce water sources, and this is a huge fight among them. Most of them die, but the very few survivors, they have to fight all the time. If you have in this population you put water and then a plain full of food, suddenly they will explode, but the virus will also explode.

LOBET: This is very similar to what many scientists believe happened in 1993, in the American southwest, with the hanta virus outbreak that killed 26 people. Rain interrupted a drought. Suddenly, the mice had more food and their numbers exploded, bringing them and their deadly feces into more contact with people. But the idea that such a rodent-borne epidemic wiped out the Mexican Indian population four centuries ago, is new.

CLEVELAND: The story of Cocoliztli and the whole idea that a lot of what I learned in college about Mexican history and the history of the new world could be wrong, basically. I was really shocked by that.

LOBET: Acu–a and the others stress the drought rodent connection is only a hypothesis. There is another theory to explain why rodents might suddenly have come into more contact with people. Drs. Marr and Kiracofe suggest that when the Spanish demanded the Indians grow and store wheat, it meant people moving in on the rodents territory, and the stored wheat created a magnet for them.


LOBET: Two days later, back in Oaxaca, Matthew Terrell stumbles out of the forest, with 40 pounds of slices from downed Douglas Fir imprinting his pack straps onto his bones. They'll take the slices and the core samples back to Arkansas to analyze, to see if they've pushed the climate record back, or, at least, bolstered their shakier data.

TERRELL (in background): I mean, I feel like I was going to blow my knee out, man.

LOBET: Though they're fascinated by the past, their real hope is that it will help understand current climate change. Dr. Acu–a, too, believes climate could influence future plagues, and he likes to remind Americans that great civilizations like Mexico's Mayan and Tule empires collapsed in mid-splendor, probably because of desiccating drought.

ACUNA: Most epidemics happen in the worst drought in the last 2000 years. We have been very, very lucky not to have something like that, and nobody can say we will not have that in the future.

LOBET: It's hard to say if we're in the middle of our splendor as a civilization. Our mastery of agriculture can seem breathtaking. But it still depends on rainfall. It's something Acu–a says he can't help contemplating during his commute, as he crests the hills that separate suburban Cuernavaca from the smoky bowl of Mexico City and looks down on the largest concentration of people in human history.

For Living on Earth, I'm Ingrid Lobet.



Medical History article on Huey Cocoliztli
Tree-Ring Laboratory
Dr. Marr's website on ten plagues of Egypt
Dr. Marr's work">


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