Genetic diversity of Theileria equi and Babesia caballi infecting horses of Central-Southern Italy and preliminary results of its correlation with clinical and serological status

Babesia caballi and Theileria equi are tick-borne pathogens causing equine piroplasmosis infecting the Equidae family in which they cause significant sanitary and economic losses. Furthermore, equine piroplasmosis is included in the World Animal Health Organization (OIE) notifiable diseases list with possible movement restrictions for positive horses. Thirty-nine EDTA and whole-blood samples collected during 2013 and 2014 from symptomatic and asymptomatic horses of Central-Southern Italy were included in the present study either because of their strongly positive results in Real Time (RT) PCRs targeting the 18S rRNA gene specific for each piroplasm and/or due to their serological ELISA/18S rRNA RT-PCR discordant results. A nested PCR amplifying the hypervariable V4 region of the 18S rRNA gene of both piroplasms was performed on all samples. T. equi positive samples were also analysed with a PCR targeting the equi merozoite antigen 1-gene (EMA-1). The sequences obtained were thirty for T. equi, 25 of which were for the hypervariable V4 region of the 18S rRNA gene and 13 for the EMA-1 gene, with eight samples positive for both targets, while only six 18S rRNA gene sequences were retrieved for B. caballi. The phylogenetic analysis results are as follows: T. equi sequences of the 18S rRNA gene clustered in three different phylogenetic groups, respectively in the A (15), B (9) and C (1) while those of B. caballi in the A (1), B1 (3) and B2 (2) groups. T. equi sequences for EMA-1 gene clustered in A (11) and in B (2). This analysis confirms that both T. equi and B. caballi sequences present a genetic heterogeneity independently of their geographical location, similar to that reported by other authors. Statistical associations were evaluated between phylogenetic groups of T. equi 18S rRNA gene and each of the following variables, using Fisher's exact test: clinical signs, serological ELISA/ 18S rRNA RT-PCR discordant results and T. equi EMA-1 negativity. The different groups were found to be statistically related to the presence of signs (less present in group B samples), to ELISA negativity/18S rRNA RT-PCR positivity (more seronegative samples in group B). No statistical analysis was performed for the B. caballi as the number of sequences available was insufficient and for the EMA - 1 sequences which almost all grouped in the same cluster. The results here obtained provide additional information about T. equi and B. caballi sequences, which could also be used to verify the performance of serological and molecular diagnostic methods.