Serological evidence of <i>Rickettsia</i> in horses and survey of tick-borne agents in ticks from horses and wildlife in the state of Pernambuco, Brazil

Tick-borne diseases are among the most widespread vector-borne infections, including zoonoses caused by bacterial and protozoal microorganisms. This study consisted of a serosurvey for Rickettsia spp. in 270 horses from 11 farms in the coastal region of Pernambuco, Brazil. Through the indirect immunofluorescence assay (IFA) based on antigens of five Rickettsia species, 164 (60.7%) horses were seroreactive to Rickettsia spp., with seroreactivity among farms ranging from 10 to 100%. Through molecular analysis, all 270 horse blood DNA samples tested negative by PCR assays targeting Anaplasmataceae family or genus Borrelia agents. A total of 1,852 ticks was collected from horses and identified as 1,850 Dermacentor nitens Neuman, 1897, and two Rhipicephalus microplus (Canestrini, 1888). No rickettsial DNA was amplified from horse ticks. Additionally, 48 tick specimens were collected from 14 wild vertebrates from the same study region, and identified into six species: Amblyomma fuscum Neumann, 1907, Amblyomma longirostre (Koch, 1844), Amblyomma nodosum Neumann, 1899, Amblyomma rotundatum Koch, 1844, Amblyomma varium Koch, 1844, and Ornithodoros mimon Kohls, Clifford & Jones, 1969. Twenty-five of these ticks were processed by molecular analysis, which resulted in no amplification of DNA from Anaplasmataceae, Piroplasmida, Borrelia, or Coxiella. However, three adults of A. nodosum contained DNA of Rickettsia parkeri Lackman et al., 1965 strain NOD, and two larvae of A. longirostre contained DNA of Rickettsia amblyommatis Karpathy et al. (2016). This study provides serological evidence of exposure to spotted fever group (SFG) rickettsiae in horses and reports two SFG agents infecting ticks from wildlife in Northeastern Brazil.