Six people in California have reportedly caught a “severe and fatal” tickborne disease named Rocky Mountain spotted fever (RMSF), with three dying from the infection.
According to a Morbidity and Mortality Weekly Report by the Centers for Disease Control and Prevention (CDC), the six cases were reported to the California Department of Public Health between July 2023 and January 2024.
All those infected had caught the disease after exposure to the bacteria Rickettsia rickettsii via ticks in Tecate, Mexico, near the U.S. border.
While northern Mexico has a high incidence of RMSF due to many free-roaming dogs with brown dog ticks, Tecate has not previously been known to be a high-risk RMSF region.
“This outbreak highlights a newly recognized location in Baja California with high RMSF risk,” the CDC said in the report.
RMSF is a potentially fatal bacterial infection caused by Rickettsia rickettsii bacteria, transmitted to humans through the bite of infected ticks, primarily the American dog tick, the Rocky Mountain wood tick and the brown dog tick.
“There are over 100 hard tick species that transmit an array of pathogens,” Peter Krause, a senior research scientist in epidemiology at Yale School of Public Health and Yale School of Medicine, told Newsweek. “Keep free of tick-infested vegetation such as brush and wooded areas.”
Early symptoms include fever, headache, nausea, vomiting, muscle pain, lack of appetite, and sometimes abdominal pain. A few days after the fever starts, a spotted red rash often appears, typically on the wrists and ankles and spreading to other body parts.
Severe cases can involve organ damage, particularly to the brain, heart and lungs, and may result in long-term complications or death if untreated.
“Early treatment with antibiotics lowers the risk of overall mortality to between 3 and 5 percent. Untreated cases have a from 13 percent to 25 percent rate of mortality,” the Mississippi Department of Public Health explains.
Most cases occur in the United States, particularly in the southeastern and south-central states, in regions with large numbers of American dog ticks and Rocky Mountain wood ticks. Mexico also sees several cases where brown dog ticks are prevalent.
Over 60 percent of cases are in North Carolina, Oklahoma, Arkansas, Tennessee and Missouri alone.
RMSF cases are reported under a broader category called Spotted fever rickettsiosis (SFR), which also includes cases of Pacific Coast tick fever, rickettsialpox and Rickettsia parkeri rickettsiosis. In 2022, there were 1,292 cases of SFR in the U.S., according to CDC data, and California saw an incidence rate of 0.31 per million people.
“The identification of six confirmed cases of RMSF in southern California over 6 months is unusual; during 2011–2019, an average of one confirmed RMSF case per year was reported for the state of California,” the CDC report said.
According to the CDC report, the six California cases included a 17-month-old male, male siblings aged 4.5 and 3 years, a 13-year-old boy, a 17-year-old girl and a 65-year-old man.
All patients had lived in or traveled to Tecate within 8 days of symptoms appearing, and all had had exposure to dogs in the region, with one reporting a tick bite.
The 17-month-old recovered after treatment with antibiotics, as did the 3-year-old boy and the 13-year-old boy. Unfortunately, the 4.5-year-old boy, the 65-year-old man and the 17-year-old girl all died from the infection due to cardiac failure and respiratory failure, respectively.
“This outbreak highlighted a new area of RMSF risk in Mexico and underscored the need for health care provider awareness on both sides of the U.S.-Mexico border to treat suspected RMSF patients quickly with doxycycline to reduce risk for death,” the report states.
“The rapid clinical progression of RMSF from a moderately severe illness to a life-threatening disease necessitates early initiation of doxycycline, as soon as the disease is suspected clinically, without waiting for confirmation of the diagnosis.”
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References
Kjemtrup, A. M., Hacker, J. K., Monroe, M., Williams, V., Lines, C., Lopez, K., Paddock, C. D., Carpenter, A., Salzer, J. S., Villalba, J. A., Bhatnagar, J., Shah, S., Iniguez-Stevens, E., Efthemeou, T. C., Hernandez, V., Vugia, D. J., & Kramer, V. L. (2024). Severe and Fatal Rocky Mountain Spotted Fever After Exposure in Tecate, Mexico — California, July 2023–January 2024. MMWR Morbidity and Mortality Weekly Report, 73(47), 1069–1075. https://doi.org/10.15585/mmwr.mm7347a1
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