Seroprevalence and epidemiology of typhus group Rickettsia infection in Texas

Abstract

Background: Typhus group Rickettsia (TGR) are a subgroup of vector-borne bacterial pathogens in the genus Rickettsia. Flea-borne TGR rickettsiosis in humans is most often caused by R. typhi. Clinical disease characteristically presents as fever, rash, headache, nausea, and vomiting, making it difficult to distinguish clinically from other flu-like syndromes. If left untreated or with delayed treatment, severe and life-threatening disease can develop. TGR is a growing public health concern in Texas, where surveillance data indicates increasing incidence of flea-borne rickettsiosis, from 157 reported cases in 2008 to 738 in 2018. Fleas that transmit TGR take bloodmeals from a variety of mammalian species, including farm, wild, and domestic animals. For this reason, individuals with frequent animal contact or who engage in outdoor activities with abundant wildlife could be at heightened risk of TGR exposure. Greater understanding of the local epidemiology in the southern United States, where the ecology is conducive to TGR endemicity, in needed. Methods and materials: As part of an attempt to understand the epidemiology of zoonotic and vector-borne diseases in Texas, we conducted serologic screening among individuals engaged in hunting and/or ranching across the state of Texas, enrolled from 2015 to 2018. Serum was tested for IgG to TGR using a commercial ELISA kit, tested in parallel for IgG to Spotted Fever Group Rickettsia (SFGR), and confirmed by immunofluorescence assay. Utilizing interview data on demographics, behaviors, and other potential exposures, we defined characteristics associated with TGR seropositivity. Results: Among 631 study participants, ages 6 to 81 (median 48) years and 80% male, 35% had IgG against TGR by ELISA. To characterize the local epidemiology, spatial distribution of TGR seropositivity are demonstrated, with hotspot and overlay analyses. Potential risk factors for TGR exposure are reported as odds ratios with 95% confidence intervals. Conclusion: This new evidence of highly prevalent TGR exposure among a presumed high-risk population from across Texas suggests that TGR infections may be going under-recognized and underreported, with higher incidence than previously thought, at least in some groups. These findings can drive targeted educational campaigns to raise awareness about risk factors and disease prevention, facilitate early clinical recognition, and inform surveillance strategies.