Tick-Borne Fever Epidemic In Mexico May Be Spreading Into U.S.

An epidemic of Rocky Mountain spotted fever transmitted by brown dog ticks that began in Mexico in 2008 has not been contained and researchers warn that it may be spreading into the United States. According to a study in the CDC's Emerging Infectious Diseases Journal, the risk to humans of catching the disease is heightened because the brown dog tick is "cosmopolitan" and prefers a dog as its host.

Officials in Mexico declared the epidemic an "epidemiologic emergency" in 2015 and as of 2018, around 4,000 people have been affected by it. The study says a fatal 2014 case of Rocky Mountain spotted fever in Imperial County, California was probably associated with the Mexican epidemic.

Since 2000, the incidence of Rocky Mountain spotted fever in the United States has increased four fold, which the CDC says is in part due to increased transmission by the brown dog tick. The disease is responsible for more human deaths than any other tick-borne disease in North America.

The study says more information is needed to understand why the epidemic emerged.

"The RMSF epidemic in Mexicali has not been contained and may be spreading to other parts of Baja California and into the United States," the researchers write.

The CDC notes dog spay and neuter programs, treatment of houses against ticks and use of a tick collar have helped contain more localized and smaller epidemics.

In 2016, more than 4,269 cased of spotted fever Rickettsiosis were reported in the United States but its unclear how many of those were specifically Rocky Mountain spotted fever. According to the CDC, most cases of the disease in the United States have been spread by bites of infected dermacentor or American dog ticks.

Signs and symptoms of Rocky Mountain spotted fever include:

• Fever
• Headache
• Rash
• Nausea
• Vomiting
• Stomach pain
• Muscle pain
• Lack of appetite

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