Ehrlichia sp. infection in carthorses of low-income owners, Southern Brazil

• Anti-Ehrlichia sp. antibodies were detected in carthorses by a comprehensive serological survey with three different methods;.
• Detection of Ehrlichia DNA, sequencing and phylogenetic analysis of 16 S rRNA and dsb genes confirmed infection;.
• This is the first report of a natural infection of this bacteria in horses from South America;.
• Clinical signs and the tick vector remain unknown.

Although well established in dogs, Ehrlichia sp. infection has been scarcely reported in horses. The aim was to perform a comprehensive serological and molecular survey for the detection of Ehrlichia spp. in carthorses from Southern Brazil. Blood samples from 190 carthorses from Paraná State were sampled. Horses were also tested for Borrelia burgdorferi and Anaplasma phagocytophilum. Anti-Ehrlichia sp. antibodies were detected by a commercial rapid ELISA, and immunofluorescence antibody assays (IFA) with E. chaffeensis and E. canis as crude antigens. The molecular and phylogenetic analysis of Ehrlichia sp. was based on 16 S rRNA and dsb genes. A total of 52 (27.4%), 4 (2.1%), and 3 (1.6%) horses were positive for Ehrlichia spp., Anaplasma spp. and Borrelia burgdorferi, respectively, by the commercial rapid ELISA. Thirty-eight (20.0%) and 37 (19.5%) horses showed anti-E. chaffeensis and anti-E. canis antibodies by IFA, respectively. One blood sample that also showed anti-E. chaffeensis antibodies was PCR positive for the 16 S rRNA and dsb genes of Ehrlichia spp., showing an identity of >98.0% to the uncultured Ehrlichia sp. previously detected in Brazilian jaguars (Panthera onca). Anti-Ehrlichia sp. antibodies and Ehrlichia DNA were detected in carthorses from Southern Brazil, which may post public health concerns due to intimate contact with low-income owners. This is the first report of a natural infection of this bacteria in horses from South America. Clinical signs and the tick vector remain unknown.