Ticks Target People as Climate Warms

Graphic by Annabel Driussi

by Natasha Lasky, ODP Contributing Writer

A new study presented during the American Society of Tropical Medicine and Hygiene Annual Meeting revealed that 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 rise. 

Why This Matters: Ticks are thriving on a warming planet as their numbers skyrocket and tick season lasts longer. This poses a serious risk to people and wildlife as ticks have more opportunities to target their hosts. 

RMSF is a life-threatening illness that causes fevers, rashes, severe headaches, swelling of the eyes and hands, nausea, and vomiting. Though it can be treated with antibiotics, if left untreated, RMSF kills 30% of those infected. RMSF among humans is on the rise— in 2017, there were more than 6,000 cases, a 12-fold increase compared to the 495 cases reported in 2000.

Likewise, cases of Lyme disease in the United States have doubled over the past twenty-years to about 30,000 cases a year. And we’re also seeing ticks that carry Lyme disease spread to northern New England and the midwest, while other ticks that are normally found in the south have spread to New York and New Jersey. 

In addition, bacteria-based tick-borne diseases are becoming more and more common: anaplasmosis, which can cause fever and chills, and a rare but fatal condition called Powassan virus.

As Joel Breman, the president of ASTMH, in the statement:

“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.”


The Experiment: Before this study, there was some initial research that suggested brown dog ticks were more likely to bite humans in warmer weather.

To test this theory, a team of researchers at the UC Davis School for Veterinary Medicine built two large wooden boxes and connected them with a clear plastic tube. One box contained a dog, and the other contained a graduate student — 20 ticks were placed into the plastic tube, and for twenty minutes, the researchers observed which way the ticks chose to crawl. They performed this test in both 74 degree and 100-degree temperatures. 

Luckily, mesh barriers kept the ticks from biting either participant, but it was clear to the researchers that as the temperature increased, the ticks were two and a half times more likely to move towards the human rather than the dog

It’s still unclear exactly why hotter temperatures make ticks more likely to bite humans. Study author  Lauren Backus, had a theory: “At hotter temperatures, they might be more eager to find a host, because at higher temperatures, they’re more likely to dry out and die faster. And so that might be why they’re going toward the host more aggressively and more quickly for survival.” In any case, those venturing outdoors should heed this warning, especially as numbers of casual hiking have spiked during the COVID pandemic. 


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