As Earth Warms, the Diseases That May Lie Within Permafrost Become a Bigger Worry


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By Sara Goudarzi, Scientific American – 30 October 16
Source: Reader Supported News

 

Scientists are witnessing the theoretical turning into reality: infectious microbes emerging from a deep freeze

 

This past summer anthrax killed a 12-year-old boy in a remote part of Siberia. At least 20 other people, also from the Yamal Peninsula, were diagnosed with the potentially deadly disease after approximately 100 suspected cases were hospitalized. Additionally, more than 2,300 reindeer in the area died from the infection. The likely cause? Thawing permafrost. According to Russian officials, thawed permafrost—a permanently frozen layer of soil—released previously immobile spores of Bacillus anthracis into nearby water and soil and then into the food supply. The outbreak was the region’s first in 75 years.

Researchers have predicted for years that one of the effects of global warming could be that whatever is frozen in permafrost—such as ancient bacteria—might be released as temperatures climb. This could include infectious agents humans might not be prepared for, or have immunity to, the scientists said. Now they are witnessing the theoretical turning into reality: infectious microorganisms emerging from a deep freeze.

Although anthrax occurs naturally in all soil and outbreaks unrelated to permafrost can occur, extensive permafrost thaw could increase the number of people exposed to anthrax bacteria. In a 2011 paper published in Global Health Action, co-authors Boris A. Revich and Marina A. Podolnaya wrote of their predictions: “As a consequence of permafrost melting, the vectors of deadly infections of the 18th and 19th centuries may come back, especially near the cemeteries where the victims of these infections were buried.”

And permafrost is indeed thawing—at higher latitudes and to greater depths than ever before. In various parts of Siberia the active layer above permafrost can thaw to a depth of 50 centimeters every summer. This summer, however, there was a heat wave in the region, and temperatures hovered around 35 degrees Celsius—25 degrees warmer than usual. The difference possibly expanded or deepened the thaw and mobilized microorganisms usually stuck in rigid earth. Although scientists have yet to calculate the final depth, they postulate that it is a number that has not been seen in almost a century. Permafrost thaw overall could become widespread with temperatures only slightly higher than those at present, according to a 2013 study in Science. Heat waves in higher latitudes are becoming more frequent as well.

What thawing permafrost could unleash depends on the heartiness of the infectious agent involved. A lot of microorganisms cannot survive in extreme cold, but some can withstand it for many years. “B. anthracis are special because they are sporulating bacteria,” says Jean-Michel Claverie, head of the Mediterranean Institute of Microbiology and a professor at Aix-Marseille University in France. “Spores are extremely resistant and, like seeds, can survive for longer than a century.”

Viruses could also survive for lengthy periods. In 2014 and 2015 Claverie and his colleague Chantal Abergel published their findings on two still infectious viruses from a chunk of 30,000-year-old Siberian permafrost. Although Pithovirus sibericum and Mollivirus sibericum can infect only amoebas, the discovery is an indication that viruses that infect humans—such as smallpox and the Spanish flu—could potentially be preserved in permafrost.

Human viruses from even further back could also make a showing. For instance, the microorganisms living on and within the early humans who populated the Arctic could still be frozen in the soil. “There are hints that Neandertals and Denisovans could have settled in northern Siberia [and] were plagued by various viral diseases, some of which we know, like smallpox, and some others that might have disappeared,” Claverie says. “The fact that there might be an infection continuity between us and ancient hominins is fascinating—and might be worrying.”

Janet Jansson, who studies permafrost at the Pacific Northwest National Laboratory in Washington State, is not worried about ancient viruses. Several attempts to discover these infectious agents in corpses have come up empty, she notes. She does advocate, however, for further research to identify the wide range of permafrost-dwelling organisms, some of which could pose health risks. To accomplish that goal, she and others are using modern molecular tools—such as DNA sequencing and protein analysis—to categorize the properties of unknown microorganisms, sometimes referred to as microbial dark matter.

The likelihood and frequency of outbreaks similar to the one in Siberia will depend on the speed and trajectory of climate change. For instance, it is possible that another heat wave will expose the carcasses of animals infected by anthrax, Revich says. “The situation on the Yamal Peninsula has shown that the risk of the spread of anthrax is already real,” he adds.

In effect, infectious agents buried in the permafrost are unknowable and unpredictable in their timing and ferocity. Thus, researchers say thawing permafrost is not our biggest worry when it comes to infectious diseases and global warming. The more immediate, and certain, threat to humans is the widening geographical ranges of modern infectious diseases (and their carriers, such as mosquitoes) as the earth warms. “We now have dengue in southern parts of Texas,” says George C. Stewart, McKee Professor of Microbial Pathogenesis and chair of the department of veterinary pathobiology at the University of Missouri. “Malaria is seen at higher elevations and latitudes as temperatures climb. And the cholera agent, Vibrio cholerae, replicates better at higher temperatures.”

Unlike the zombie microbes lurking in the permafrost, modern spreading diseases are more of a known quantity, and there are proved ways to curb them: mapping trends, eliminating mosquito-breeding sites and spraying insecticides. Of course, dramatically lowering fossil-fuel emissions to combat climate change could tackle both threats—the resurgence of ancient and deadly pathogens and the widening ranges of infectious diseases—in one shot.

The Plagues of Global Warming


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By Elizabeth Kolbert, The New Yorker, 27 February 15
Source: Reader Supported News

The black rat—also known as the ship rat, the roof rat, and the house rat—is actually gray. It has large ears and a tail that’s longer than its body. The black rat (Rattus rattus) probably evolved in tropical Asia, and then was spread around the world by humans—first by the Romans and later by European colonists. According to Juliet Clutton-Brock, the author of “A Natural History of Domesticated Mammals,” it has been blamed for causing “a greater number of deaths in the human species than any natural catastrophe or war.” But perhaps the rat has gotten a bad rap?

A paper published the other day in the Proceedings of the National Academy of Sciences, which quickly made headlines all around the world, argues that the prevailing theory of how the Black Death spread is unfair to rats. Really, the authors of the study contend, the animal responsible was a Central Asian species like the great gerbil. (Great gerbils are only distantly related to the fuzzy rodents that American kids keep as pets, though they may look a lot alike to parents.)

The authors of the study were trying to address one of the mysteries about the Black Death. Why, after killing something like twenty-five million people in Europe in the mid-fourteenth century, did outbreaks of plague keep flaring up and then dying down again? (The Great Plague of London, in the mid-seventeenth century, killed roughly a fifth of the city’s population.) The prevailing theory is—or was—that bacteria responsible for the plague, Yersinia pestis, lived on Europe’s black-rat population. The rats transmitted the bacteria to fleas, which, episodically, transmitted them to humans. But the scientists who conducted the PNAS study concluded that there were no “permanent plague reservoirs in medieval Europe.”

Instead, they posit, the plague bacterium kept being reintroduced to Europe from Asia, where it lived on the native rodent populations. They came to this conclusion after comparing tree-ring records from Europe and Asia with records of plague outbreaks. What they found was that plague seemed to show up at port cities in Europe several years after climate conditions favored a burst of population growth among rodents in Central Asia. (This theory does not completely exonerate black rats, as they would still have helped their Asian rodent brethren spread the disease once it reached Europe.)

“We show that, wherever there were good conditions for gerbils and fleas in Central Asia, some years later the bacteria shows up in harbor cities in Europe and then spreads across the continent,” one of the authors of the study, Nils Christian Stenseth, a biologist at the University of Oslo, told the BBC.

Plague is no longer a worry in Europe, although there are still occasional outbreaks in other parts of the globe. What’s perhaps the most important insight from the study has little to do with Yersinia pestis or giant gerbils. It’s that climate and human health are, in significant though often roundabout ways, related. As the climate changes, this has important—and, at the same time, hard to predict—implications.

The list of diseases (and disease vectors) that could potentially be affected by climate change is a long and various one. It includes tick-borne diseases, such as Lyme disease, and mosquito-borne diseases—dengue fever, West Nile virus, malaria. It also includes waterborne diseases, such as cholera, and fungal diseases, such as valley fever. An upcoming issue of Philosophical Transactions B, a journal of Britain’s Royal Society, is wholly devoted to the subject of “climate change and vector-borne disease.”

Rising temperatures may already be contributing to the spread of some diseases, like chikungunya, a mosquito-borne virus that, not long ago, was confined to Africa and Asia. (The name of the virus, from Kimakonde, a language spoken in Tanzania and Mozambique, means “to become contorted,” which is what happens to the virus’s victims, who experience severe joint pain.) In recent years, cases have shown up in Italy and the Caribbean, and, just last year, in Florida. While the recent spread of chikungunya probably has more to do with global trade and travel than with climate change, the mosquito that transmits the virus seems to be able to survive in more and more places as the globe warms.

“All the blocks are falling into place,” Walter Tabachnick, the director of the Florida Medical Entomology Laboratory, at the University of Florida, told NPR a few weeks ago. “You’ve got to be worried about this.”

Which brings us back to giant gerbils. If the new PNAS study is correct, then millions in Europe died because the climate conditions were sometimes favorable for these rodents a quarter of the way around the world. The indirect nature of the connection makes it hard to foresee what warming will mean for human health, which—in case you needed it—is another thing to worry about.