The Same Genes Are Associated with Protozoan Infections in Domestic Horses and Donkeys

Piroplasmoses are tick-borne diseases of various vertebrate hosts caused by blood parasites belonging to the genera Babesia and Theileria. Individual horses and donkeys remaining free of infection with Theileria equi and others more prone to infection with Babesia caballi were observed. This suggests, along with reports on associations between protozoan infections and host genetic variability in other species, the existence of specific genes involved in resistance/susceptibility to protozoan infections in Equids.

Local resident horse (Camargue, Murgese, Romanian, Arab) and donkey (Italian, Jordanian and Kenya local breeds) populations permanently exposed to infections with T. equi and B. caballi were analyzed to identify candidate host genotypes associated with infection. The Italian and Jordanian horses and donkeys were from the same areas, sharing environment, ticks and both parasites.

Randomly selected microsatellites, candidate immunity-related gene SNPs, and major-histocompatibility complex (MHC)-linked microsatellites in linkage disequilibrium with an MHC class II (Eqca-DRA) gene were used as markers. Based on a diagnostic PCR, horses were classified as double positive, Theileria equi positive, Babesia caballi positive and negative. MHC markers, the genes SLC11A1, IL17A and the microsatellite AHT004 were associated with the infections status in both species and across populations within each species. Some alleles showed associations with infection across breeds within one species. Associations between the same genes (or even alleles) and disease observed in two genetically distinct populations are more likely to be biologically plausible. The associations observed here thus indicate a role of the host genome in susceptibility to infection with these important parasites.