After raging fires subside, their impact on peoples’ health will linger. During and immediately after wildfires, increased hospital visits document the direct toll of smoke and flames — from burns to trouble breathing. But the more insidious ways the fires affect people months or even years ahead has been more difficult to follow.
Animals who’ve survived previous blazes can help us better understand those long-term effects, scientists say. In California, where fire season has grown longer and more intense as a result of climate change, cats and monkeys are offering insights.
After 2008 wildfires exposed roughly 4,000 monkeys at the California National Primate Research Center at the University of California, Davis, “I looked at this as an opportunity to study how a true natural exposure might influence their long term respiratory health as well as their immune function,” says Lisa Miller, who leads the respiratory diseases unit at the center. It’s one of seven centers in the US supported by the National Institutes of Health that studies primates in order to better understand human diseases. “We have our own little town or village, if you will, of monkeys,” Miller says. “What they were exposed to is no different than what the humans that were in this area were exposed to.”
In humans, inhaling smoke can trigger asthma attacks and aggravate other preexisting lung and heart diseases. While there’s plenty of evidence of these risks, much of our understanding of these threats is based on research on air pollution in cities over time. It’s easier to study consistent sources of pollution, like city traffic, than it is to chase down data from unpredictable wildfires. Particulates that wreak havoc in the body once inhaled are present in tailpipe emissions and smoke, but there’s growing evidence that burning vegetation can have different levels of toxicity than burning gasoline. And surviving a fire comes with other stressors that might impact health.
“No epidemiologist to my knowledge has been able to tease out the long term effects for fires,” Loretta Mickley, a senior research fellow at Harvard, tells The Verge. She was part of a team that studied agricultural fires in Indonesia in 2015 and estimated that the resulting haze led to 100,000 premature deaths in the region, most within one year. Mickley and other researchers from Harvard and Columbia used established relationships between air quality and health outcomes to come to that number, which was much larger than the number of deaths documented by the governments of Indonesia, Malaysia, and Singapore. “There’s no question that when people are breathing these tiny particles, the human body will suffer,” Mickley says.
But when it comes to understanding longer-term effects, “you’d have to have very detailed data before and after a fire event,” she says. “So for example, in Indonesia, we just don’t have on-the-ground data of health that is granular enough.”
Miller’s research on primates, in contrast, is able to get more granular data because she’s been studying the primates for so long. Miller studied rhesus monkeys born just before the wildfire smoke swept through the area where the primates live in outdoor facilities, tracking their health over time. They ended up developing lungs about 20 percent smaller than monkeys born after the fire, she found. As they get older, their lungs are getting stiffer, too. They’ve got reduced lung function in comparison to counterparts who weren’t exposed. Using blood samples to mimic an infection in the lab, she found that the immune systems of monkeys born just before the fires appear to be compromised, Miller says. She points out, however, that the researchers didn’t see a significant rise in morbidity or mortality and that adult monkeys who inhaled the smoke didn’t cope with the same long-term effects.
The research has important implications for how human kids and babies might be adversely affected by smoke, according to Miller. “The takeaway is that our kids are likely to be the most vulnerable to these types of exposures,” she says. “The health outcomes of those exposures are going to stay with them for the rest of their lives.”
There’s also more to worry about than smoke with fires. Cats that survived the Tubbs Fire that ripped through Santa Rosa, California, in 2017 and Paradise, California, in 2018 wound up with some troubling heart problems, a recent study from the University of California, Davis found. Of 51 rescued felines studied, more than half developed heart muscle thickening, which could eventually lead to an enlarged heart or congestive heart failure, and 30 percent either had blood clots or were at higher risk of developing blood clots, which could lead to a stroke or sudden death. Researchers are still unsure whether these outcomes were the result of stress, smoke inhalation, burns, or a combination of all three. However, 82 percent of the cats recovered and were reunited with their owners or found new homes.
In humans, more severe burns are associated with more dramatic cardiovascular changes. But in the cats, many of those with moderate burns still had dramatic heart changes. That finding, along with more research, might eventually inform whether doctors need to be just as wary of cardiovascular issues in patients with moderate burns as they are with those whose burns are more severe. “Our hope is understanding, is this just a cat thing?” says Catherine Gunther-Harrington, one of the authors of the new study. “Or should we be more aware of the cardiovascular effects of wildfires across all species?”
“They’re not humans, so there’s always that limitation,” Miller says of using animal models to understand human health. But in the absence of data on humans, these animals can help fill in gaps in our understanding. “The hard data comes from animal models,” she says.