Two articles/studies published in the journal, Philosophical Transactions of the Royal Society B, discuss how climate change and warmer temperatures are affecting infectious diseases and their affect on us.
First, an article by Harold W. Manter Laboratory of Parasitology at the University of Nebraska-Lincoln affiliated zoologist, Daniel Brooks warns that humans can expect more such illnesses to emerge in the future, as climate change shifts habitats and brings wildlife, crops, livestock, and humans into contact with pathogens to which they are susceptible but to which they have never been exposed.
Brooks and his co-author, Eric Hoberg, a zoologist with the U.S. National Parasite Collection of the USDA’s Agricultural Research Service, have personally observed how climate change has affected very different ecosystems. During his career, Brooks has focused primarily on parasites in the tropics, while Hoberg has worked primarily in Arctic regions.
“Over the last 30 years, the places we’ve been working have been heavily impacted by climate change,” Brooks said in an interview last week. “Though I was in the tropics and he was in the Arctic, we could see something was happening.”
Changes in habitat mean animals are exposed to new parasites and pathogens.
For example, some lungworms in recent years have moved northward and shifted hosts from caribou to muskoxen in the Canadian Arctic. Scientists also have observed that climate shifts in the late Pliocene and Quaternary periods resulted in new species of pocket gophers, with the lice that infect them following suit.
But for more than 100 years, scientists have assumed parasites don’t quickly jump from one species to another because of the way parasites and hosts co-evolve.
Brooks calls it the “parasite paradox.” Over time, hosts and pathogens become more tightly adapted to one another. According to previous theories, this should make emerging diseases rare, because they have to wait for the right random mutation to occur.
But it turns out such jumps happen more quickly than anticipated. Even pathogens that are highly adapted to one host are able to shift to new ones under the right circumstances.
“We have to admit we’re not winning the war against emerging diseases,” Brooks said. “We’re not anticipating them. We’re not paying attention to their basic biology, where they might come from and the potential for new pathogens to be introduced.”
In addition, the journal features a study by researchers at the Cary Institute of Ecosystem Studies in Millbrook, NY, which demonstrate that in the northeastern United States, warmer spring temperatures are leading to shifts in the emergence of the blacklegged ticks that carry Lyme disease and other tick-borne pathogens. At the same time, milder weather is allowing ticks to spread into new geographic regions.
Cary Institute ecologist and co-author of the study, Dr. Richard S. Ostfeld notes, “Nearly two decades of data revealed climate warming trends correlated with earlier spring feeding by nymphal ticks, sometimes by as much as three weeks. If this persists, we will need to move Lyme Disease Awareness Month from May to April.”
Risk of tick-borne illness is shaped by complex interactions among pathogens, ticks, and host animals. Take the case of Lyme disease: blacklegged ticks acquire the bacterium that causes Lyme when they feed on small mammals that harbor Borrelia burgdorferi. Ticks seek a single blood meal at each life stage: larva, nymph, and adult. Larval ticks are born free of the Borreliabacterium. Tiny infected nymphs pose the greatest threat to people.
Dr. Taal Levi of Oregon State University led the emergence analysis; he performed the work while a Postdoctoral Associate at the Cary Institute. Levi explains, “Understanding when ticks are active, and at what life stage, is essential to predicting tick-borne disease spread. Pathogens that cause a lasting host infection, such as the Lyme disease bacterium, benefit from a lag between nymphal and larval feeing. The same might not be true of other pathogens, like Powassan virus, that are transmitted when larvae and nymphs feed simultaneously.”
“Results suggest that significant climate warming may reduce risk of anaplasmosis and the Powassan virus, but increase Lyme disease risk, particularly in the Upper Midwest where tick feeding patterns are likely to become more asynchronous,” Levi said.
With Ostfeld emphasizing, “Here in the Northeast, warming is already having an effect, and people need to be tick-vigilant before May, as potentially infected nymphal ticks are searching for their blood meals earlier and earlier.”