“The history of interactions among disparate peoples is what shaped the modern world through conquest, epidemics and genocide. Those collisions created reverberations that have still not died down after many centuries, and that are actively continuing in some of the world’s most troubled places.”
(Jared Diamond. Guns, Germs and Steel: The Fate of Human Societies)

“History is a version of past events that people have decided to agree upon”
(Napoleon Bonaparte)

The issue of past and future climate change in relation to infectious diseases has become an ongoing source of intense and increasingly polarizing debate. Science journalist, Linda Marsh’s recently released, Fevered: How a Hotter Planet Will Harm Our Health and How We Can Save Ourselves, joins the discussion with a fresh look at the decimation of Pre- Colombian civilizations at the time of the Spanish conquest. Scholars have long speculated that climate change and lethal epidemics played a major role in the collapse of the Mayan civilization. In this book, Marsh focuses her attention on the impact of climate change and disease upon the much later empire of the Mexicas, commonly referred to now as Aztecs. Her subsequent conclusions are primarily based upon the investigations of Mexican Dr. Rodolfo Acuna-Soto, a Harvard trained infectious disease specialist and research professor at the National Autonomous University of Mexico, in Mexico City.

In 1519 when Hernan Cortes and his army arrived in what is now Mexico, there were approximately 25 million indigenous people living there. By the next century as few as 1.2 million had survived. This drastic population reduction has been attributed to a lack of immunity to measles, mumps and smallpox; which are known to have devastated huge populations of North American indigenous, as a result of contact with Europeans and their descendants. In Mexico, records show that a smallpox epidemic erupted in 1519 and 1520 shortly after the Spanish arrived, which proved fatal to between 5 and 8 million natives. Later in 1545 and then1576, an even more virulent epidemic erupted in Mexico City and then swept through the highlands, with a death toll as high as 17 million. Dr. Rodolfo Acuna-Soto was puzzled as to how a disease epidemic attributed to the Europeans could prove so deadly, so long after they arrived, since the Aztecs and other tribes who had survived the previous plague would have conferred immunity to their descendants.

In search of answers, Acuna-Soto spent over a decade examining ancient records left by 16th century Spanish priests, who together with the Aztecs, endeavored to preserve records of their history, culture and language. He found that these texts also documented climatic events such as storms and frosts as well as illness. Within these accounts of plagues of cocoliztli, (Nahuati for “pest”), he found descriptions of a disease that seemed even more virulent than smallpox. Acuna-Soto then turned to extensive diaries kept by Fernando Hernandez, who was personal physician to King Phillip II and Surgeon General of New Spain during a second catastrophic outbreak of 1576. Dr. Hernadez described a highly contagious and rapidly advancing scourge, usually fatal; after just a few days of raging fevers, jaundice, tremors, dysentery, chest and abdominal pain, dry black tongue, extreme thirst, delirium and seizures, as well as blood gushing from nose and ears. To Acuna-Soto, these descriptions were not all that consistent with smallpox or any other known European disease, but rather with some form of hemorrhagic fever. He then wondered, if indeed Europeans were not responsible for transmitting this disease , how and why did it come about ? A word of caution here; because there is, in fact, (although extremely rare), a lethal form of hemorrhagic smallpox known by the folk name of “the purples”, due to dark colorations caused by massive internal and sub-cutaneous bleeding.

As Acuna-Soto’s research continued, he noticed a pattern; while the plague had been preceded by years of severe drought, the outbreaks only occurred during wet weather. To confirm his observations he consulted with a team of dendro-chronologists, who study tree ring patterns in order to date climate patterns. Together they compared 16th century accounts of epidemics with tree ring patterns found in 450 Douglas firs in a remote region of central Mexico near Durango. According to the tree ring data, most of the severe and sustained drought along the North American continent, during the last 500 years, took place during the 16th century. However, there were heavy downpours around 1545 and 1576 which coincided with the outbreaks of cocolitztli. As a result, Acuna-Soto concluded that the deadly cocolitzli that decimated the Aztecs was an indigenous hemorrhagic fever virus spread by rodents. During the drought, he reasoned, food and water were scarce, and then when the rains returned, the rat population suddenly proliferated and spread the lethal scourge. (Linda Marsa, “Climate, Not Spaniards, Brought Diseases That Killed the Aztecs”, Discover Magazine, August, 2013).

While such conclusions seem reasonable, one is left to wonder if only the Aztecs and other natives were affected and why this cocoliztl virus did not spread back to Europe? This question then leads us into larger epidemiological questions about the transmission of various diseases between Europeans and the New World inhabitants. While various theories abound, researchers have failed to reach a definitive consensus.

In the case of syphilis, for example, its origin remains unknown. In present time, there are two primary theories. While some maintain that this disease was carried from the Americas back to Europe by Christopher Columbus, others also argue that it did exist in Europe but was previously unrecognized. Meanwhile, the role of climate change in the origin and transmission of disease remains an ongoing topic of research, discovery and controversy.

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