Rocky Mountain spotted fever risk is greater than expected

A recent study is providing new insight on the spread of Rocky Mountain spotted fever, which is transmitted from dogs to people through ticks. The researchers are creating models that may ultimately help to predict, or even prevent, future outbreaks of the deadly disease.

Rocky Mountain spotted fever can cause serious organ damage in humans that may lead to death if it is not caught early and treated within the first five  days. The disease can also cause serious illness in dogs if it is not treated during the early stages.

Historically, the disease was carried by the American dog tick or Rocky Mountain wood tick. In 2003, the brown dog tick was identified as a new carrier during an outbreak in Arizona. In the years that have followed, the Rickettsia rickettsii bacteria that causes spotted fever has spread to brown dog ticks across the American Southwest and parts of Mexico.

A team of researchers led by Dr. John VandenBrooks at Midwestern University set out to investigate why the brown dog tick emerged as a new carrier. The experts conducted a detailed analysis of brown dog ticks, Rocky Mountain spotted fever  infections in canines and humans, and climate data in Arizona, New Mexico, California and Mexico.

“Our results indicate that the spread of Rocky Mountain spotted fever involves a combination of factors and that the vectoring capacity of the brown dog tick may be spreading outside of the region,” said study co-author Kayla Allwardt. “This could put a much larger portion of the country at risk. Identifying the highest risk regions is essential to protecting canine and human health.”

For the analysis, the researchers collected dog and tick serum samples from 25 sites and mapped relevant environmental factors.

“We found three genetically distinct populations of ticks, which vary in the percentage of ticks that carry the R. rickettsii bacteria,” said study co-author Nicolette Roe. “These differences are a major contributor to the variation in Rocky Mountain spotted fever cases we see across the region.”

Importantly, the researchers discovered high rates of Rocky Mountain spotted fever infection in dogs across areas where no human cases had been reported. Of the 16 counties surveyed, the experts identified two as having a high risk for an outbreak, 10 at medium risk, and only four were at low risk.  

The research was presented at the meeting Experimental Biology 2022.

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By Chrissy Sexton, Earth.com Staff Writer