Spatial Distribution of Equid Exposure to Rickettsia spp. in Goiás State, Midwestern Brazil

This study sought to investigate the presence of anti-<i>Rickettsia</i> spp. antibodies in georeferenced serum samples from equids across all regions of the state of Goiás, while also presenting variables that indicate risk factors for the circulation of rickettsiae, and evaluating the presence of rickettsial DNA in ticks collected from equids and the surrounding environment in the municipalities of Uruaçu and Porangatu, located in the northern region of the state. A total of 1156 equid serum samples provided by the Goiás Agricultural Defense Agency (Agrodefesa) were analyzed for antibodies against 4 <i>Rickettsia</i> antigens. Additionally, 39 blood samples were collected from equids during a 3-day field expedition in January 2024, alongside 938 ticks collected from both animals and the environment. In total, 297 adult ticks were randomly selected for molecular analysis and tested by qPCR targeting the rickettsial <i>glt</i>A gene. Positive samples were further analyzed using cPCR to target the <i>omp</i>A and <i>glt</i>A genes. Results revealed that 9.6% (111/1156) of the serum samples were seroreactive to at least one <i>Rickettsia</i> antigen. Among these, 36% had antibodies against <i>Rickettsia rickettsii</i>, 18.9% against <i>Rickettsia parkeri</i>, 69.4% against <i>Rickettsia amblyommatis</i>, and 14.4% against <i>Rickettsia bellii</i>. Furthermore, the possible antigen responsible for a homologous reaction was found in 3.6% of equids for <i>R. rickettsii</i>, and in the same proportion for <i>R. bellii</i>, while 23.4% of animals showed antibodies for <i>R. amblyommatis</i>, and none exhibited a homologous reaction to <i>R. parkeri</i>. Meanwhile, 28.2% of the serum samples collected during the field expedition had antibodies against <i>R. amblyommatis</i>, with 72.7% identifying <i>R. amblyommatis</i> as the antigen involved in the homologous reaction. In the logistic regression analysis, the variables of education level, altitude below 500 m, and presence of female mules demonstrated a positive effect on seropositivity. Ticks from animals were identified as <i>Amblyomma cajennense</i> sensu lato, <i>Amblyomma sculptum</i>, <i>Dermacentor nitens</i>, and <i>Rhipicephalus microplus</i>, while environmental ticks were identified as <i>A. cajennense</i> s.l., <i>A. sculptum</i>, and <i>Amblyomma nodosum</i>. In the qPCR assays, two specimens of <i>A. cajennense</i> s.l., one of <i>A. sculptum</i>, and one of <i>D. nitens</i> amplified a fragment of the <i>glt</i>A gene. Of these, one <i>A. cajennense</i> s.l. specimen amplified a fragment of both the <i>omp</i>A and <i>glt</i>A genes, and one <i>A. sculptum</i> specimen amplified a fragment of the <i>glt</i>A gene through conventional PCR. Sequencing confirmed the detection of <i>R. amblyommatis</i>. These findings highlight the presence of anti-<i>Rickettsia</i> spp. antibodies in equid serum samples from all regions of the state of Goiás, emphasizing the important role of equids as sentinels for <i>Rickettsia</i> spp. To our knowledge, this study represents the largest effort to detect anti-<i>Rickettsia</i> spp. antibodies in equid serum samples in Brazil. Additionally, it is the first nationwide investigation of its kind conducted in collaboration with the Agricultural Defense Agency (Agrodefesa), serving as a significant example of the One Health approach.