Survey on the Presence of Equine Tick-Borne Rickettsial Infections in Southcentral United States.
Authors: Duncan Kathryn T, Sundstrom Kellee D, Hunt Devery, Lineberry Megan W, Grant Amber, Little Susan E
Journal: Journal of equine veterinary science
Summary
Tick-borne rickettsial diseases represent an understudied threat to equine health in North America, prompting researchers to investigate the prevalence of Rickettsia and Ehrlichia species in ticks collected from horses across Oklahoma and to assess serological evidence of infection in the equine population. Duncan and colleagues examined 352 ticks harvested from infested horses alongside serum samples from both infested and non-infested animals, using polymerase chain reaction sequencing to identify rickettsial pathogens and immunological assays to detect antibodies against these agents. The survey revealed that over 71% of tick-infested horses carried at least one infected tick, with Rickettsia species present in approximately 26% of all ticks tested (predominantly *R. amblyommatis*), whilst Ehrlichia species occurred in roughly 3% of specimens; significantly, nearly 30% of examined horses demonstrated circulating antibodies to Ehrlichia spp., indicating current or previous exposure, despite an absence of antibodies to *R. rickettsii* or *Anaplasma* spp. These findings establish that rickettsial pathogens are circulating within equine tick populations in the southcentral United States and that horses are developing immune responses to at least some of these agents, creating an urgent need for clinicians, farriers and equine managers to investigate whether these infections contribute to recognised disease presentations and to establish appropriate surveillance and prevention protocols in affected regions.
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Practical Takeaways
- •Tick-borne rickettsial infections are present in Oklahoma horses and their tick vectors; veterinarians should consider these agents as potential causes of clinical disease and counsel clients on tick control
- •Serologic evidence of Ehrlichia exposure in nearly 30% of horses suggests these infections may be more clinically relevant than previously recognized and warrants further investigation of associated clinical signs
- •Effective tick management programs are essential for horses in the southcentral United States to reduce exposure to these rickettsial pathogens
Key Findings
- •Rickettsia spp. were identified in 25.9% of ticks collected from horses in Oklahoma, with R. amblyommatis comprising 80.2% of detections
- •Ehrlichia spp. were identified in 2.8% of ticks tested, with E. ewingii most frequently detected
- •71.4% of horses with tick infestations hosted at least one tick containing a rickettsial agent
- •29.6% of horses examined had circulating antibodies to Ehrlichia spp., indicating past or current infection, while none had antibodies to R. rickettsii or Anaplasma spp.