Warming Planet Ups Risk of Deadly Tick-Borne Fever

November 16, 2020 – Climate change, already linked to more frequent forest fires, longer droughts and more tropical storms, may also increase the risk of contracting the potentially fatal tick-borne disease known as Rocky Mountain spotted fever, new research suggests.

When temperatures rise, the brown dog tick, which carries the disease-causing bacteria, is more than twice as likely to shift its food preference from dogs to humans, according to researchers at the University of California at Davis. They will present their research today at the annual meeting of the American Society of Tropical Medicine and Hygiene.

“This risk [of contracting the disease] may increase as climate change forces us to have more frequent warm weather environments, ”says researcher Laura Backus, a graduate student at UC Davis.

Rocky Mountain spotted fever, transmitted by various types of ticks in the United States, has a 30% death rate and can kill quickly if not treated within 5 days of onset of symptoms. according to the CDC. Symptoms include fever, rash, severe headache, swelling around the eyes and the back of the hands, and stomach problems such as vomiting or nausea.

A blood test can help make the diagnosis. It is usually treated with the antibiotic doxycycline for 5 to 7 days.

Cases of Rocky Mountain spotted fever and related illnesses, known collectively as spotted spotted rickettsiosis, have increased dramatically over the past 20 years. In 2000, 495 cases were reported in the United States; in 2017, the total was over 6,000. Cases in 2018 have declined somewhat, according to the CDC.

Human versus dog experiment

To observe the effect of temperature on a tick’s preference to feed on dogs or people, the researchers built two large wooden boxes about 3 feet high and 2 feet wide, connected by a tube. made of transparent plastic. One person sat in one box and a dog in the other as ticks were released into the tube.

For 20 minutes, the researchers observed whether the ticks made their way towards dogs or people, once when the temperature was 74 degrees and then when it was 100 degrees.

The researchers tested the ticks in advance to make sure they weren’t infected. They placed meshes on each end of the tube, so ticks couldn’t come in contact with dogs or people.

Researchers studied two types of brown dog ticks – called temperate and tropical – both capable of carrying the disease. Ticks of the tropical lineage have shifted their preference considerably from dogs to humans; the temperate too, but less, says Backus. Researchers cannot say why.


Research suggests that “warmer climates will have a greater risk of transmission of Rocky Mountain spotted fever by this vector,” says Kathleen Walker, PhD, associate specialist and associate professor of entomology at the University of Arizona, Tucson. the results but was not involved in the study.

This tick lives in and around homes, she says. “People find these ticks in their beds.” The best prevention is to treat dogs – with a tick collar, an oral tick medicine prescribed by a veterinarian, or a topical tick preparation.

“The way these come into contact [with people] is through dogs, “says Walker.” If you protect the dog, you protect yourself.

Walker also suggests taking all tick bites seriously. “Take it off as soon as possible,” she said, using pliers to pull it off. Keep an eye on the area. If you have a fever or rash, see a doctor immediately, she says. Be sure to tell healthcare professionals that you have been bitten.

WebMD Health News


TropMed2020, American Society of Tropical Medicine & Hygiene Annual Meeting, November 16, 2020.

CDC: “Rocky Mountain Spotted Fever (RMSF)”.

Laura Backus, doctoral student, University of California, Davis.

Kathleen Walker, PhD, Associate Specialist and Associate Professor of Entomology, University of Arizona, Tucson.

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