Tick species twice as likely to target humans over dogs at high temperatures
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Ticks carrying the bacterium that causes Rocky Mountain spotted fever are more than twice as likely to feed on humans rather than dogs when temperatures increase, study results indicate.
The results, which were presented during the American Society of Tropical Medicine and Hygiene Annual Meeting, suggest that climate change may have an impact on human disease risk, researchers said.
“The findings from the use of this simple but effective laboratory experiment to gauge how rising temperatures might lead to more human infections with a very dangerous tick-borne pathogen adds to the growing evidence of the increasing connection between climate change and its impact on health,” ASTMH president Joel Breman, MD, DTPH, FASTM, said in a press release. “Climate change is moving so quickly that it is critical to keep pace with the many ways it may alter and intensify the risk of a wide range of infectious diseases, so we are better prepared to diagnose, treat and prevent them.”
According to the CDC, prior to the availability of tetracycline antibiotics, case fatality rates for Rocky Mountain spotted fever ranged from 20% to 80%. Prompt treatment is important because the disease can be rapidly fatal if not treated within 5 days of symptoms. The bacterium that causes the illness, Rickettsia rickettsii, is spread by different ticks in different areas of the U.S.
For their study, Laura Backus, MPH, DVM, a researcher at the University of California, Davis School of Veterinary Medicine, and colleagues developed two wooden boxes that were connected via a plastic tube. They had a dog and a human enter each box, distributed ticks at the center of the tube and then observed whether the ticks moved toward the dog or the human over 20-minute periods at 74°F and 100°F.
“Our work indicates that when the weather gets hot, we should be much more vigilant for infections of [Rocky Mountain spotted fever] in humans,” Backus said in the release. “We found that when temperatures rose from about 74°F to 100°F, brown dog ticks that carry the disease were 2.5 times more likely to prefer humans over dogs.”
At 100°F, the tropical lineage brown tick was significantly likelier to target the human than the dog.
Amid a rise in tick-borne illness, NIH created a plan to accelerate research regarding ticks and tick-borne pathogens last year, including Rocky Mountain spotted fever.
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Backus LH, et al. Effect of increased temperature on host selection by the brown dog tick. Presented at: American Society of Tropical Medicine and Hygiene Annual Meeting; November 15-19, 2020; virtual.
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