Texas, USA, is home to several human-biting tick species that carry and transmit bacterial pathogens, including Rickettsia, Borrelia, and Ehrlichia spp. (1–3). Since 2004, the University of North Texas Health Tick-Borne Disease Laboratory (Fort Worth, TX, USA) has performed pathogen testing of ticks removed from humans and submitted to the Texas Department of State Health Services (1,4,5). Building on previous surveillance efforts, we further analyzed the temporal and geographic distributions of tick species and tickborne bacteria in Texas. The data reflected human–tick interactions rather than natural tick activities and distributions and could be useful in informing public health risk in Texas.

Entomologists at the Texas Department of State Health Services identified tick species morphologically and classified unidentified specimens by tick mitochondrial 16S rRNA gene analysis. They used PCRs and Sanger sequencing (1) to determine the presence of bacteria: Borrelia by using the flaB gene target, Ehrlichia by using the dsb gene target, and Rickettsia by using the rompA gene target. We excluded 2020 data from the temporal analysis because of testing delays caused by the COVID-19 pandemic.

A total of 1,625 ticks (9 species) from Texas were tested from October 1, 2014, through September 30, 2021. The most frequently submitted tick species was Amblyomma americanum (48.9%), followed by Dermacentor variabilis (21.2%), A. maculatum (11.9%), Ixodes scapularis (10.0%), Rhipicephalus sanguineus (3.8%), and A. mixtum (3.4%) (Appendix Table 1). Nymphs represented a substantial proportion of A. americanum (42.8%) and A. mixtum submissions (60.0%), and larvae were 2.1% (A. americanum) and 3.6% (A. mixtum) of submissions. By contrast, the other submitted species were mostly adults. The female-to-male ratio was close to 1 (0.87–1.2) for most species, except for I. scapularis (90.7%) and D. variabilis (62.3%) tick submissions, which were mostly female.

Figure 1

Figure 1. Box plot graph displaying temporal patterns of ticks submitted in Texas, USA, 2014–2021. A) Adult ticks; B) nymphs; C) Rickettsia amblyommatis and R. tamurae subspecies ...

Adult A. americanum, A. maculatum, D. variabilis, and I. scapularis tick submissions demonstrated clear temporal patterns (Figure 1, panel A; Appendix Table 2). Adult A. americanum submissions were much higher in May–July. We observed the highest adult A. maculatum tick submissions in August. Submission of adult I. scapularis ticks peaked in March, and D. variabilis ticks peaked in June. We observed no obvious temporal patterns in nymphal A. americanum or A. mixtum submissions (Figure 1, panel B).

We identified 9 bacterial species from ticks and an overall prevalence rate of 26.0%, largely comprising spotted fever group rickettsiae. Rickettsia amblyommatis was the most common bacterium, with the following prevalence rates in each tick species: A. mixtum, 34.6%; A. americanum, 26.8%; R. sanguineus, 1.6%; D. variabilis, 0.58%; and A. maculatum, 0.5% (Appendix Table 1). R. tamurae subspecies buchneri, the second most frequent bacterial species, was detected only in I. scapularis ticks (85.2% positive rate, 90% in females, whereas all male ticks tested negative). R. amblyommatis and R. tamurae subsp. buchneri–positive ticks demonstrated temporal patterns similar to the overall submission patterns of A. americanum and I. scapularis ticks; peaks occurred from May–July for R. amblyommatis and in March for R. tamurae subsp. buchneri (Figures 1, panel C; Appendix Table 2). Lacking clinical evidence, the pathogenicity of R. amblyommatis is unclear. R. tamurae subsp. buchneri is thought to be a nonpathogenic endosymbiont of I. scapularis ticks, providing essential nutrients for tick survival (6). The presence of those 2 organisms might reduce the transmission of other pathogenic Rickettsia spp. in ticks (6,7).

Figure 2

Figure 2. Geographic distribution of tick submissions and bacteria-positive ticks in Texas, USA, 2014–2021. A) Amblyomma americanum ticks. B) Dermacentor variabilis ticks. C) A. maculatum ticks. D) ...

Tick submissions primarily originated from eastern, central, and southern Texas, with a few from the panhandle and far western counties (Figure 2, panels A–F). The most tick submissions were from Travis County (n = 199), followed by Anderson County (n = 134). The most A. americanum tick submissions were from Anderson County (n = 130), and the most D. variabilis tick submissions were from Uvalde County (n = 35). The most A. maculatum (17), I. scapularis (n = 37), and R. sanguineus (n = 6) tick submissions were from Travis County. Nearly all (97.5%) I. scapularis submissions were from eastern Texas (east of 98°W longitude). All A. mixtum submissions originated from the southeastern area of the state, below 31°N latitude and east of 100°W longitude, with the most from Cameron County. The most R. amblyommatis ticks were from Anderson County and the most R. tamurae subsp. buchneri positive ticks were from Travis County (Figure 2, panels G–H). Ticks carrying Candidatus B. lonestari, E. chaffeensis, and R. parkeri were mainly from eastern and central Texas (Figure 2, panel I). Similar to our previous report, the prevalence of Candidatus B. lonestari (0.5%) and E. chaffeensis (0.4%) n A. americanum ticks and R. parkeri (5.2%) in A. maculatum ticks remained low and were found primarily in eastern and central Texas (1,4,5).

In conclusion, the temporal and geographic patterns of human–tick encounters and tickborne pathogens provide valuable guidance for outdoor activities and public health planning. The overall bacterial prevalence rate (26%) in ticks was slightly higher than our previous report (23%), highlighting the need for continued tick pathogen surveillance in this region.

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Suggested citation for this article: Zhang Y, Mitchell EA, Kilgore RJ, Allen MS. Surveillance of ticks and tickborne Borrelia, Ehrlichia, and Rickettsia spp., Texas, USA, 2014–2021. Emerg Infect Dis. 2026 Jul [date cited]. https://doi.org/10.3201/eid3208.251104