Detection of Ehrlichia sp. in Amblyomma sculptum parasitizing horses from Brazilian Pantanal wetland

Abstract

Bacteria of the genus Ehrlichia are transmitted by ticks and also are an important cause of infection in wild and domestic mammals. Infection with Ehrlichia spp. has been reported in horses, especially in the USA, Nicaragua and Brazil. In this study, we report the parasitism by Amblyomma sculptum, Rhipicephalus microplus and Dermacentor nitens ticks in horses from a ranch located in south Pantanal wetland. Molecular and serological analyzes to determine infection by Ehrlichia spp. in horses and their respective ticks were carried out. A total of 12 horses were submitted to blood collection to investigate antibodies by indirect immunofluorescence assay (IFA) using Ehrlichia canis crude antigens and to be tested by polymerase chain reaction (PCR) in order to amplify fragments of the 16S rRNA, dsb, groEL and sodB gene of Ehrlichia spp. A total of 164 tick specimens were removed from horses, stored in isopropanol and later identified as D. nitens, A. sculptum and R. microplus. DNA from ticks were extracted and subjected to the same PCR assays to detect Ehrlichia spp. Anti-Ehrlichia spp. antibodies were detected in five/12 (41.7 %) horses by IFA, with antibody titers ranging from 40 to 160. All horse DNA samples were negative for the 16S rRNA, dsb, groEL and sodB of Ehrlichia spp. One A. sculptum female was positive to all target genes of Ehrlichia. This tick was parasitizing an Ehrlichia-seropositive horse with antibody titer of 80. Nucleotide sequences of 16S rRNA, dsb, groEL and sodB genes showed close relationship with different strains of Ehrlichia detected in wild mammals, Amblyomma ticks and horses from Brazil and Argentina. Detection of anti-Ehrlichia sp. antibodies suggests that horses have been exposed to an ehrlichial agent in the Pantanal. Future studies on Ehrlichia infection should be carried out to better elucidate and to bring new information about equine ehrlichiosis, since these animals are important hosts of ticks in the Brazilian Pantanal wetlands.

Keywords: Ehrlichiosis; Horse; Pantanal; Tick-borne disease; Ticks.