Rocky Mountain Spotted Fever Risks Examined

dog with ticks
Many of the dogs researchers examined in Mexicali were infested with ticks. Some of the dogs carried thousands of ticks. Janet Foley/UC Davis

In Mexicali, Mexico, an uncontrolled epidemic of Rocky Mountain spotted fever, one of the deadliest tickborne diseases in the Americas, has affected more than 1,000 people since 2008.

A binational team of researchers led by the University of California, Davis, has conducted the first comprehensive study to examine risk factors for the disease in Mexicali. Researchers examined dogs, ticks, and surveyed households in 200 neighborhoods. Half of the neighborhoods in the study had diagnosed human cases of the disease. They discovered that, even though citywide only one in 1,000 ticks was infected, there were neighborhoods at very high risk, where almost one in 10 ticks were infected.

“If you live in one of these high-risk neighborhoods and you get five brown dog tick bites, that means you have a pretty good chance of being exposed to Rocky Mountain spotted fever,” said lead author Janet Foley, with the Department of Medicine and Epidemiology at the UC Davis School of Veterinary Medicine.

Rocky Mountain spotted fever is spread by the brown dog tick, which feeds on dogs and people, and thrives in hot, arid climates. Previous studies have shown that poverty, numerous stray dogs and brown dog ticks increased the risk of getting Rocky Mountain spotted fever. In Mexicali, risks were higher along the edges of poorer neighborhoods or outside of the city in rural areas.

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