In this cross-sectional study, the Johnston County Osteoarthritis (JoCo OA) project aimed to evaluate the potential association between prior exposure to tick-borne diseases (TBDs) and chronic musculoskeletal symptoms or osteoarthritis. TBDs, excluding Lyme disease, such as spotted fever group rickettsiosis (SFGR), ehrlichiosis, and galactose-α-1,3-galactose (α-gal) syndrome, are a growing public health concern. Despite 50,000 cases of TBD being reported in the US in 2019, the study found no link between the presence of antibodies for Ehrlichia or Rickettsia (seropositivity) and chronic musculoskeletal symptoms or osteoarthritis.
Out of the 605 participants who attended the fourth visit of the JoCo OA project, serum samples were available from 488 individuals for testing. Of those participants, 8.6% (95% CI, 5.9%-11.3%) for Ehrlichia immunoglobulin G (IgG), 17.1% (95% CI, 12.6%-21.5%) for Rickettsia IgG, and 19.6% (95% CI, 15.3%-23.8%) for α-gal immunoglobulin E (IgE) levels above 0.1 IU/mL. Of these, only the α-gal IgE levels were linked with knee pain, aching, or stiffness (mean ratio 1.30; 95% CI, 1.09-1.56tbd). There were no associations found between antibodies to Rickettsia, Ehrlichia, and α-gal and symptomatic radiographic knee osteoarthritis.
“Despite only 84 individuals (17.2%) recalling a tick bite in the past 5 years, 178 (36.5%) had either α-gal IgE level greater than 0.1 IU/mL, a positive test result for SFGR IgG antibodies, or a positive test result for Ehrlichia IgG antibodies, suggesting high levels of tick exposure in this cohort,” according to investigators. “Given that not every tick is a vector of an infectious pathogen or an allergen (for example, entomological studies suggest that <10% of lone star ticks are infected with Ehrlichia24), the findings highlight that human-tick interactions are common.”
3 Key Takeaways
- Despite a low percentage of participants recalling a tick bite in the past 5 years, the study revealed a high level of tick exposure in the cohort.
- Men were more likely than women to have antibodies indicating exposure to certain tick-borne infections such as SFGR and higher α-gal IgE levels. For female participants, current smoking status and recent tick bites were significant factors in these infections.
- The absence of an association between musculoskeletal symptoms and most tick-borne infections was a reassuring finding.
The study found that men were more likely than women to have antibodies indicating exposure to certain tick-borne infections such as SFGR (odds ratio (OR,) 3.28; 95% CI, 1.99-5.41), and higher α-gal IgE levels exceeding 0.1 IU/mL (OR, 3.25; 95% CI, 2.05-5.17). Additionally, individuals who experienced a tick bite attachment within the past 5 years were more likely to have detectable antibodies for SFGR (OR, 2.44; 95% CI, 1.39-4.26). However, upon further analysis by gender, it was determined that being a current smoker and having experienced a tick bite within the past 5 years were statistically significant factors only for female participants. Out of the 94 individuals who had α-gal IgE levels above 0.1 IU/mL, 7 (7.4%) also tested positive for Ehrlichia IgG, and 28 (29.8%) had detectable IgG antibodies to SFGR.
“It had the ability to leverage an established longitudinal cohort with a complex sampling strategy that provided weighted population prevalence rates for Ehrlichia, SFGR, and α-gal exposure,” the investigators wrote. “We are not aware of a comparable cohort wherein participants are enrolled on the basis of place of residence within a similar area of high exposure to multiple tick species.”
However, there were several limitations to the study and its findings. One limitation of the study is that a single positive antibody test (IgG titer) does not necessarily indicate active disease. Moreover, the study did not collect detailed information on symptoms or past diagnoses, which limits the ability to assess the overall impact of these infections. As a result, using these findings to estimate the overall burden of disease is not appropriate. The accuracy of the results is further complicated by the potential for cross-reactivity among different species of Ehrlichia or SFGR. Secondly, since IgG levels can remain elevated for years following exposure, it was not possible to determine a time-based relationship between exposure and musculoskeletal symptoms. Nonetheless, the lack of any association found between musculoskeletal symptoms and tick-borne infections is reassuring.
Overall, although there was no association between musculoskeletal symptoms and SFGR and Ehrlichia antibodies, α-gal IgE was associated with knee pain, aching, or stiffness. Further investigation is needed into the pathogenesis of α-gal syndrome and interventions to reduce human-tick interactions.
Reference
1. Zychowski DL, Alvarez C, Abernathy H, et al. Tick-borne disease infections and chronic musculoskeletal pain. JAMA Netw Open. Published January 11, 2024. Accessed January 26, 2024. doi:10.1001/jamanetworkopen.2023.51418
