Beyond Rocky Mountain spotted fever: investigation of the presence and diversity of spotted fever Rickettsia species in ticks submitted from forestry workers.

Ticks present a significant risk to people in the southern United States, particularly those who spend time outdoors, as ticks can transmit agents that cause various diseases. This study evaluated the risk of exposure to ticks positive for spotted fever group (SFG) Rickettsia species among forestry workers. From 2017 to 2021, forestry workers passively collected ticks during field surveys for the USDA Forest Service's Forest Inventory and Analysis program. We screened 1395 ticks for SFG-Rickettsia, including Amblyomma americanum (51.5% positive, N = 1,279), A. maculatum (40% positive, N = 10), and Dermacentor variabilis (22.6%, N = 106). The agent of Rocky Mountain spotted fever, R. rickettsii, was not detected; however, 7 different SFG Rickettsia species were identified. Rickettsia amblyommatis was the most common, present in 95.7% of A. americanum ticks. The pathogenic R. parkeri was rare, detected in 2 A. americanum nymphs and 2 A. maculatum males only. Several Rickettsia species, such as R. montanensis, R. monacensis, Candidatus R. andeanae, and R. tamurae subsp. buchneri, were identified in D. variabilis. Some of these species are suspected to be pathogenic. Rickettsia-positive ticks were detected year-round, with the highest prevalence in Tennessee and Kentucky, possibly due to larger sample submissions, which may have increased detection rates. Dermacentor variabilis were less likely to be Rickettsia-positive compared to A. americanum. Male ticks were less likely to carry Rickettsia than females and nymphs. The presence of Rickettsia-positive ticks found in this study poses a risk to forestry workers, emphasizing the importance of ongoing surveillance and education to prevent tick-borne infections.