A Lethal Disease Hidden in Plain Sight in Mexico

It’s among the deadliest of severe infectious diseases. It moves rapidly to damage all tissues and organs. It causes telltale red spots to erupt on the body.

Rocky Mountain Spotted Fever (RMSF) is also bacterial threat that continues to spread in the Americas because of a lack of research and awareness, according to experts at a Nov. 14, 2024, session at the annual meeting of the American Society of Tropical Medicine & Hygiene.

RMSF’s case fatality rate (CFR) in recent years has rivaled that of dengue, yellow fever, and bubonic plague. Its CFR has ranged from 5% in Arizona to nearly 40% in parts of Mexico and above 50% in Sao Paulo, Brazil, according to data presented by the Christopher Paddock of the CDC’s Rickettsial Zoonoses Branch.

A Scourge in Northern Mexico
The disease is a significant public health threat in northern Mexico, where nearly 10,000 cases have been documented in the last 15 years, said Gerardo Álvarez-Hernández, of the University of Sonora. 

RMSF was initially recognized in Mexico in the 1940s—decades after it was first documented in the Bitterroot valley in Montana. However, awareness of the disease plummeted after cases fell in the subsequent decades. The disease began to resurge in the early 2000s, especially in the country’s northern border region with the U.S.

“The disease in Mexico is a social and public health problem unfairly affecting vulnerable individuals and communities,” said Álvarez-Hernández.

The bacterium Rickettsia rickettsii spreads via several tick species that feed on stray dogs and infect humans. The lack of control of both the ticks and stray dogs means lead to outbreaks among vulnerable populations, disproportionately affecting people living in poverty, per a July 2024 PLOS Neglected Tropical Diseases article by Gerardo Álvarez-Hernández and colleagues. 

Rapid Infection
Part of the reason for disease’s high fatality rate there is that it initially causes nondescript symptoms including fever, malaise, and headache, which delay diagnosis and treatment. The rash—which can appear as pinpoint dots or large red splotches—occurs in three to four days after initial symptoms, Álvarez-Hernández said. From onset of symptoms, patients can die in just seven or eight days—or even sooner. Survivors can face “permanent cognitive deficits and amputations resulting from gangrene of extremities and appendages,” according to the PLOS article.

Death can be avoided if the patient is treated early with the antibiotic doxycycline.

What’s Needed? 
Álvarez-Hernández and others have called for:

• More robust epidemiological surveillance to track the disease and improve data on the number of cases.
• Greater education of people in communities in endemic areas to increase awareness of RMSF.
• Better training for physicians about the signs of RMSF infection and best practices in care and treatment.
• Improved diagnostic capabilities.

Álvarez-Hernández also advocates for official recognition of RMSF as a neglected tropical disease, which would draw greater political and scientific interest as well as funding for research and intervention programs. 

“After 20 years working with this, we need political will,” said Álvarez-Hernández. "We need resources. We need budgets. We need scientific effort to deal with the disease.”

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