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Tick-borne relapsing fever: an interstate outbreak originating at Grand Canyon National Park
Abstract:
During the 1973 summer season, 27 employees and 35 overnight guests at the North Rim, Grand Canyon National Park, Arizona, acquired febrile illnesses compatibel with relapsing fever. Sixteen cases were confirmed by finding Borrelia spirochetes in peripheral blood smears or inoculated Swiss mice. Retrospective surveys of 278 employees and 7247 guests at the park revealed that acquisition of illness was significantly associated with the persons sleeping in rustic log cabins and acquiring bites of "unknown" insects. From rodent nesting materials found in the walls and attics of cabins where cases had occurred, infective Ornithodoros hermsi ticks were recovered. Exceptional activity of ticks in human populations appeared to have resulted from a decreased population of the ticks' usual rodent hosts. Vector control activities consisted of spraying the cabins with residual insecticide, removing nesting materials, and "rodent proofing." This outbreak, the largest yet identified in North America, extends the known range of a principal vector and establishes the North Rim as an endemic source of tick-borne relapsing fever.
Insights
An outbreak of tick-borne relapsing fever occurred at Grand Canyon National Park in 1973. The illness was linked to Ornithodoros hermsi ticks, likely due to a decrease in their usual rodent hosts.
Area of Science:
- Epidemiology
- Infectious Diseases
- Arthropod-borne Illnesses
Background:
- Relapsing fever is a bacterial infection transmitted by ticks or lice.
- Tick-borne relapsing fever (TBRF) is caused by Borrelia species and transmitted by soft ticks.
- Grand Canyon National Park is a popular tourist destination with unique ecological factors.
Observation:
- In 1973, 27 employees and 35 guests at Grand Canyon's North Rim developed febrile illnesses consistent with relapsing fever.
- Sixteen cases were confirmed by detecting Borrelia spirochetes.
- Illness was associated with sleeping in rustic cabins and unknown insect bites.
Findings:
- Infective Ornithodoros hermsi ticks were recovered from rodent nesting materials in cabins.
- A decreased population of the ticks' usual rodent hosts likely led to increased tick activity in humans.
- This was the largest North American outbreak of TBRF identified to date.
Implications:
- The North Rim of Grand Canyon is established as an endemic source of tick-borne relapsing fever.
- The known geographic range of Ornithodoros hermsi, a principal vector, has been extended.
- Public health awareness and vector control measures are crucial in preventing future outbreaks.