Non–Lyme disease, tick-borne illnesses — such as spotted fever group rickettsiosis (SFGR), ehrlichiosis, and alpha-gal syndrome (AGS) — are emerging public health threats, but whether prior tick exposures are responsible for long-term complications, such as musculoskeletal symptoms or osteoarthritis, has been unclear.
Many patients attribute their nonspecific long-term symptoms, such as musculoskeletal pain, to previous illnesses from tick bites, note authors of a study published in JAMA Network Open. But the researchers, led by Diana L. Zychowski, MD, MPH, with the Division of Infectious Diseases at the University of North Carolina at Chapel Hill, found that Ehrlichia or Rickettsia seropositivity was not associated with chronic musculoskeletal symptoms, though they write that “further investigation into the pathogenesis of [alpha-gal] syndrome is needed.”
Tick-Borne Illness Cases Multiplying
Cases of tick-borne illness (TBD) in the United States have multiplied in recent years. More than 50,000 cases of TBD in the United States were reported in 2019, which doubled the number of cases over the previous 2 decades, the authors note.
Most of the cases are Lyme disease, but others — including SFGR and ehrlichiosis — represent an important public health threat, especially in southeastern states, the authors write. Cases of ehrlichiosis, for example, transmitted by the lone star tick, soared more than 10-fold since 2000.
The goal of this study was to evaluate whether there was an association between prior exposure to TBDs endemic to the southeastern United States and chronic musculoskeletal symptoms and radiographic measures of osteoarthritis.
Researchers analyzed 488 blood samples from the fourth visit (2017-2018) of the Johnston County Osteoarthritis (JoCo OA) project, an ongoing population-based study in Johnston County, North Carolina. JoCo OA participants include noninstitutionalized White and Black Johnston County residents 45 years old or older with osteoarthritis.
They measured seroprevalence of Rickettsia- and Ehrlichia-specific immunoglobulin G (IgG) as well as alpha-gal immunoglobulin E (IgE) in patient samples. Only alpha-gal IgE was linked in the study with knee pain, aching, or stiffness. Antibodies to Rickettsia, Ehrlichia, and alpha-gal were not associated with radiographic, symptomatic knee osteoarthritis.
“To our knowledge,” the authors write, “this study was the first population-based seroprevalence study of SFGR, Ehrlichia, and [alpha]-gal.”
The study also found a high prevalence of TBD exposure in the cohort. More than a third (36.5%) had either an alpha-gal IgE level greater than 0.1 IU/mL, a positive test for SFGR IgG antibodies, or a positive test for Ehrlichia IgG antibodies.
Given that not every tick carries an infectious pathogen, the findings show human-tick interactions are common, they write.
“These findings suggest that substantial investment is required to examine the pathogenesis of these TBDs and interventions to reduce human-tick interactions,” the authors conclude.
This study was funded by a Creativity Hub Award from the University of North Carolina Office of the Vice Chancellor for Research. The JoCo OA project is supported in part by grants from the Association of Schools of Public Health/Centers for Disease Control and Prevention (CDC); and grants from the National Institute of Arthritis and Musculoskeletal and Skin Diseases. Authors reported grants from the National Institutes of Health, the CDC, and several pharmaceutical companies.