Climate change

Plague is more likely now thanks to climate change


A closed sign is posted in a parking lot near the Rocky Mountain Arsenal Wildlife Refuge warning of the plague.

A closed sign is posted in a parking lot near the Rocky Mountain Arsenal Wildlife Refuge.
Photo: David Zalubowski (PA)

The risk of plague spreading from humans to animals in the western United States has increased since 1950 thanks to climate change, news to study found. Importantly, the research yields valuable insight into how this deadly disease historically moved and developed in the United States, which can help us better understand its future.

“We want to understand where the plague (yes, ‘the plague’, which is still a common disease of wildlife) can exist in the United States, how it can exist has changed over the last century, and why the plague can exist in those places it does, and doesn’t say 20 miles down the road, ”study co-author Boris Schmid said in an email.

Yersinia pestis is the bacteria that causes plague, including this plague, the medieval black plague, which killed approximately 25 million people over four years in the 1300s. The bacteria are spread to humans from animals, the most notorious of which are rats, which carry plague-infested fleas with them. Scientists have speculated that the plague, like many other infectious diseases, will likely increase its spread to humans as the planet warms and people come into ever closer contact with wildlife.

But there isn’t a lot of research out there on what historically are the best conditions for the plague to grow and spiral out of control. As a result, there are still a lot of big questions about the plague – like why it hasn’t spread to certain geographic areas, or why human cases don’t always overlap with where animals carry the plague. disease – which remain unanswered.

Much of the current modeling of how infectious diseases might spread with climate change is based on so-called species distribution models, or projections of how wildlife habitats might grow and switch. This type of modeling oversimplifies outbreaks by neglecting many important details about how plague bacteria interact with the environment, including things like soil type and elevation, which can help tell better stories about how it spreads from animals to humans, and why epidemics can happen in some places and not in others.

“Strangely enough, most of what we know about climate and disease comes from extrapolating the future based on the present, but we don’t know much about the recent past,” the co- study author Colin Carlson on Twitter DM.

The authors of the study went to great lengths to understand these details better. Using a wealth of historical data, including animal serology tests, human plague case records, climate records, and soil data sets, the researchers built a model to examine the relationships between these data points that could more precisely identify the conditions that favor the development of the disease and how they evolve over time. Their results were published in Global Change Biology on Friday.

The study found that rodent communities in some areas at higher elevationns were up to 40% more likely to harbor the disease, which the researchers say is due to warming since 1950. This in turn means that the risk of spreading plague from rodents to humans has also increased, though more lightly.

“It’s a big, messy, tangled system, and there are a lot of different levers controlling the ecology of the disease,” Carlson said. “But as we start to identify the bigger ones, we can look at how the key variables have changed since 1950, and it turns out that more and more of this region is starting to match the conditions that allow the plague to linger in. animals, and more and more, to make the leap into people.

Just because there is an increasing likelihood that the plague may develop through climate change doesn’t mean you need to start worrying about the second coming of the Black Death. These days, it’s fairly treatable with modern antibiotics, but it’s still not something that many people want to risk catching.

“The plague is probably of little concern, compared to the risk of wildfires, etc., when the western United States warms,” ​​Schmid said. “If you sleep in a place where you don’t get bitten by fleas, then you have eliminated the main route by which the disease spread to humans. “

But the research has important ramifications for other types of disease and a worrying look at our future. Crucial point: the study illustrates how the simple act of counting Human plague cases underestimate the amount of disease incubating in the wilderness of the western United States

“I think we are probably underestimating how much climate change could affect human and animal health,” Carlson said. “There’s this misconception that the biggest impacts will be caused by heat and disaster, and I just don’t think that’s a sure thing – I think it’s just harder to reconstruct the climate signal. for infectious diseases because they are a little more complicated biologically. But the pandemic tells us how important these diseases are to the world – even rare spillover events can have big consequences. “