Survey on the Presence of Equine Tick-Borne Rickettsial Infections in Southcentral United States.

The study aims to evaluate the risk of transmission of tick-borne rickettsial infections to horses in Oklahoma, United States. Researchers discovered the presence of Rickettsia spp. and Ehrlichia spp. in equine ticks and evidence of past or current infection with Ehrlichia spp. in Oklahoma horses.

Collection and Evaluation of Ticks and Horses

• The study focused on the collection of ticks from horses in Oklahoma for a better understanding of the possible transmission risk of tick-borne rickettsial diseases.
• The gathered ticks consisted of different species – Amblyomma americanum, Dermacentor albipictus, D. variabilis, and A. maculatum – and totaled 352. They were assessed for the presence of Rickettsia spp. and Ehrlichia spp. This was accomplished through techniques like polymerase chain reaction (PCR) and sequence analysis.
• Serum samples were handled from both infested and noninfested horses. These were assessed for antibodies to R. rickettsii using indirect fluorescence antibody testing (IFA) and Ehrlichia spp. and Anaplasma spp. through an enzyme-linked immunoassay (ELISA).

Prevalence of Rickettsial Infections in Ticks and Horses

• Results indicated that 71.4% of horses with tick infestations hosted at least one tick where a rickettsial agent was detected.
• Rickettsia spp. were found in 25.9% (91/352) of the tested ticks, with R. amblyommatis the most frequently identified species. It was present in 80.2% (73/91) of the infected ticks.
• Ehrlichia spp. were found in 2.8% (10/352) of the tested ticks with E. ewingii being the most commonly identified variant.

Evidence of Past or Current Infections in Horses

• The serologic screening revealed no horses had antibodies to R. rickettsii or Anaplasma spp., yet 29.6% of the examined horses had circulating antibodies to Ehrlichia spp. This points towards a history of infection or a current infection in these horses.

Implications for Equine Health

• The results demonstrate the presence of Rickettsia spp. and Ehrlichia spp. in equine ticks in Oklahoma and suggest a history of infection or current infection with Ehrlichia spp. in horses.
• These findings indicate the potential risk these pathogens pose to equine health, emphasizing the need for further exploration and research into the relationship between these agents and equine health.