Historical Review: Megadrought And Megadeath In 16th Century Mexico (Hemorrhagic Fever)

Rodolfo Acuna-Soto,* David W. Stahle, † Malcolm K. Cleaveland,† and Matthew D. Therrell† *Universidad Nacional Autonoma de Mexico, Ciudad Universitaria, Mexico and †University of Arkansas, Fayetteville, Arkansas, USA

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.

Figure 1. The 16th-century population collapse in Mexico, based on estimates of Cook and Simpson (1)....

Figure 2. Winter-spring precipitation reconstructed from tree ring data, Durango, Mexico ...

The epidemic of cocoliztli from1545 to 1548 killed an estimated 5 million to 15 million people, or up to 80% of the native population of Mexico (Figure 1). In absolute and relative terms the 1545 epidemic was one of the worst demographic catastrophes in human history, approaching even the Black Death of bubonic plague, which killed approximately 25 million in western Europe from 1347 to 1351 or about 50% of the regional population.

The cocoliztli epidemic from 1576 to 1578 cocoliztli epidemic killed an additional 2 to 2.5 million people, or about 50% of the remaining native population. Newly introduced European and African diseases such as smallpox, measles, and typhus have long been the suspected cause of the population collapse in both 1545 and 1576 because both epidemics preferentially killed native people. But careful reanalysis of the 1545 and 1576 epidemics now indicates that they were probably hemorrhagic fevers, likely caused by an indigenous virus and carried by a rodent host. These infections appear to have been aggravated by the extreme climatic conditions of the time and by the poor living conditions and harsh treatment of the native people under the encomienda system of New Spain. The Mexican natives in the encomienda system were treated as virtual slaves, were poorly fed and clothed, and were greatly overworked as farm and mine laborers. This harsh treatment appears to have left them particularly vulnerable to epidemic disease.

Cocoliztli was a swift and highly lethal disease. Francisco Hernandez, the Proto-Medico of New Spain, former personal physician of King Phillip II and one of the most qualified physicians of the day, witnessed the symptoms of the 1576 cocoliztli infections. Hernandez described the gruesome cocoliztli symptoms with clinical accuracy (4,5). The symptoms included high fever, severe headache, vertigo, black tongue, dark urine, dysentery, severe abdominal and thoracic pain, large nodules behind the ears that often invaded the neck and face, acute neurologic disorders, and profuse bleeding from the nose, eyes, and mouth with death frequently occurring in 3 to 4 days. These symptoms are not consistent with known European or African diseases present in Mexico during the 16th century.

The geography of the 16th century cocoliztli epidemics supports the notion that they may have been indigenous fevers carried by rodents or other hosts native to the highlands of Mexico. In 1545 the epidemic affected the northern and central high valleys of Mexico and ended in Chiapas and Guatemala (4). In both the 1545 and 1576 epidemics, the infections were largely absent from the warm, low-lying coastal plains on the Gulf of Mexico and Pacific coasts (4). This geography of disease is not consistent with the introduction of an Old World virus to Mexico, which should have effected both coastal and highland populations.

Tree-ring evidence, reconstructed rainfall over Durango, Mexico during the 16th century (6), adds support to the hypothesis that unusual climatic conditions may have interacted with host-population dynamics and the cocoliztli virus to aggravate the epidemics of 1545 and 1576. The tree-ring data indicate that both epidemics occurred during the 16th century megadrought, the most severe and sustained drought to impact north central Mexico in the past 600 years (Figure 2; [7]). The scenario for the climatic, ecologic, and sociologic mediation of the 16th-century cocoliztli epidemics is reminiscent of the rodent population dynamics involved in the outbreak of hantavirus pulmonary syndrome caused by Sin Nombre Virus on the Colorado Plateau in 1993 (8,9). Cocoliztli was not pulmonary and may not have been a hantavirus but may have been spread by a rodent host. If true, then the prolonged drought before the 16th-century epidemics would have reduced the available water and food resources. The animal hosts would then tend to concentrate around the remnants of the resource base, where heightened aggressiveness would favor a spread of the viral agent among this residual rodent population. Following improved climatic conditions, the rodents may have invaded both farm fields and homes, where people were infected through aspiration of excreta, thereby initiating the cocoliztli epidemic. The native people of Mexico may have been preferentially infected because they worked the agricultural fields and facilities that were presumably infested with infected rodents.

Figure 3. The winter-spring precipitation totals estimated for each year in Durango, 1540–1548 ...

Ten lesser epidemics of cocoliztli began in the years 1559, 1566, 1587, 1592, 1601, 1604, 1606, 1613, 1624, and 1642 (10). Nine of them began in years in which the tree-ring reconstructions of precipitation indicate winter-spring (November-March) and early summer (May-June) drought (8). But the worst epidemic of cocoliztli ever witnessed, 1545–1548, actually began during a brief wet episode within the era of prolonged drought (Figure 3). This pattern of drought followed by wetness associated with the 1545 epidemic is very similar to the dry-then-wet conditions associated with the hantavirus outbreak in 1993 (Figure 3; [9]), when abundant rains after a long drought resulted in a tenfold increase in local deer mouse populations. Wet conditions during the year of epidemic outbreak in both 1545 and 1993 may have led to improved ecologic conditions and may also have resulted in a proliferation of rodents across the landscape and aggravated the cocoliztli epidemic of 1545–1548.

The disease described by Dr. Hernandez in 1576 is difficult to link to any specific etiologic agent or disease known today. Some aspects of cocoliztli epidemiology suggest that a native agent hosted in a rain-sensitive rodent reservoir was responsible for the disease. Many of the symptoms described by Dr. Hernandez occur to a degree in infections by rodent-borne South American arenaviruses, but no arenavirus has been positively identified in Mexico. Hantavirus is a less likely candidate for cocoliztli because epidemics of severe hantavirus hemorrhagic fevers with high death rates are unknown in the New World. The hypothesized viral agent responsible for cocoloztli remains to be identified, but several new arenaviruses and hantaviruses have recently been isolated from the Americas and perhaps more remain to be discovered (11). If not extinct, the microorganism that caused cocoliztli may remain hidden in the highlands of Mexico and under favorable climatic conditions could reappear.

Acknowledgments This research was funded by the National Science Foundation, Paleoclimatology Program Grant number ATM 9986074.

Dr. Acuna-Soto is a professor of epidemiology on the Faculty of Medicine at Universidad Nacional Autonoma de Mexico. He is particularly interested in the history and environmental context of disease in Mexico.

Oldies from the hard drive:

Dry Spell Linked to Demise of the Mayan
by Paul Recer
Thu Mar 13, 2003 5:27 PM ET
Konrad A. Hughen, a geochemist at the Woods Hole Oceanographic Institution, said sediments from the Cariaco Basin in northern Venezuela clearly record a long dry siege that struck the entire Caribbean starting in about the seventh century and lasting more than 100 years. Within this dry period, said Hughen, there were years of virtually no rainfall. It was in those periods of extra dryness, he said, that the Mayan civilization went through a series of collapses before its final demise... The civilization collapsed and many of the sites were abandoned early in the 800s. They were later reoccupied only to collapse again, with some cities deserted in 860 and others in 910... A severe dry spell in 910, he said, "was the last straw."
Maya Civilization Done In By Brightening Of The Sun
The researchers found the drought episodes occurred during the most intense part of the sun's cycle. Not only that, the researchers found the droughts occurred at times when archeological evidence reflects downturns in the Maya culture, including the 900 A.D. collapse. Such evidence includes abandonment of cities or slowing of building and carving activity. Archaeologists know the Maya were capable of precisely measuring the movements of the sun, moon and planets, including Venus. Hodell said he is unaware, however, of any evidence the Maya knew about the bicentenary cycle that ultimately may have played a role in their downfall.
Drought caused by solar cycle may have doomed the Mayans
by Lee Bowman
A cyclical brightening of the sun appears to have triggered a severe 150-year drought that brought down the civilization of some of the ancient world's most accomplished astronomers, the Mayans, according to a study published today.

Writing in the journal Science, researchers at the University of Florida and the Lawrence Livermore Laboratory in California report that evidence from lake sediments indicates the Yucatan Peninsula, center of the Mayan empire, undergoes a drought every 208 years.

This interval is almost identical to a known 206-year cycle in the sun's intensity, said David Hodell, professor of geology at the university and lead author of the study.

"Looking at this series of sediment cores, it looks like changes in the sun's energy output are having a direct effect on the climate of the Yucatan and causing the recurrence of drought, which is in turn influencing the Maya evolution," Hodell said.

Hodell and colleagues had suggested in a 1995 study that the ninth-century collapse of the classic Mayan civilization came in the midst of a period that was the driest in more than 1,000 years.

They based the conclusion on analysis of a sediment core from Lake Chichancanab, on the north-central Yucatan Peninsula in Mexico. Sediments deposited layer by layer give scientists a time line of changes in climate, vegetation and land use.

In a return trip to the lake last year, the researchers collected a new series of core samples and noted layers of gypsum concentrated at certain levels in the cores. The lake's water is nearly saturated with the mineral, but during dry periods more water evaporates and the gypsum builds up at the bottom of the lake, giving a marker for ancient droughts.

Although they vary in depth, and thus the intensity of the drought they represent, the deposits occur almost exactly every 208 years. The researchers found that this cycle closely matched a previously documented solar cycle that's tracked by measuring certain radioactive substances in the soil. These tend to peak during the most intense part of a 206-year cycle of solar activity.

During those periods, the energy received by Earth from the sun increases by less than one-tenth of 1 percent, Hodell noted. But the additional energy could have been enough to change any of several circulation patterns that affect tropical weather generally and rainfall over the Yucatan specifically, the researchers said.

Climate scientists remain uncertain how much effect the long-term solar cycles have on global temperatures. Most doubt the sun has more than a minor influence on the global warming trend that's been going on for several decades, but some contend the influence is still poorly understood and may turn out to be significant.

"The Maya were highly dependent on rainfall and surface reservoirs as their principal water supply," the researchers said, so dry spells lasting decades and even centuries would have had a particularly "detrimental impact on Maya food production and culture."

The scientists found evidence not only for arid events in the ninth century, but also for several other long droughts before and after that period. Archaeological evidence suggests social upheaval resulting from each of the droughts.
Sun key to Mayan misery?
by BBC News Online's Ivan Noble
Friday, 18 May, 2001, 12:09 GMT 13:09 UK
The ancient Mayans may have had good reason for their fascination with the heavens, new research by climate historians suggests.
"It's hard for me to believe that's just a coincidence." -- David Hodell University of Florida
It seems that the Mayan homeland in central America was plagued by droughts which appear to have followed a cycle determined by the Sun.

Researchers at the University of Florida, US, analysed sediments from a lake on the Yucatan Peninsula in Mexico and found a pattern of drought repeating every 208 years.

The pattern matches a cycle of brightening and dimming in the Sun.
Sediment sample
"It looks like changes in the Sun's energy output are having a direct effect on the climate of the Yucatan and causing the recurrence of drought, which is in turn influencing the Maya evolution," said David Hodell, lead author of the study.

In 1993, Professor Hodell and his colleagues extracted a sediment sample from Lake Chichancanab in northern Yucatan documenting 9,000 years of climate history.

They found that the driest period of the current era was from AD 800 to 1000, coinciding with the collapse of the classic Mayan civilisation in the 9th Century.

This time they went back to the lake and found data that backed up their findings and pointed to other periods of drought coinciding with other declines in Mayan building activity.

They found evidence for major dry periods between 475 and 250 BC, and AD 125 and 210, which, they believe, coincides with the abandonment of pre-classic Mayan sites in the Mayan Lowlands.
Tree rings
The evidence is by no means conclusive, but, as Professor Hodell explained to the journal Science: "It's hard for me to believe that's just a coincidence.

"I think drought did play an important role, but I'm sure there were other factors, such as increasing population, degradation of the land, and socio-political change, that interacted.

"Civilisation collapse has got to be complex," he said.

Archaeologists specialising in Mayan history have described the climate evidence as compelling, but agree with Professor Hodell that it is not sufficient by itself to explain the Mayan collapse.

But other climate researchers using tree ring dating (dendrochronology) have also found evidence of a bicentennial drought cycle in step with the variation of the Sun.

The research appears in the journal Science.

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