BackgroundTransmission of arthropod-borne apicomplexan parasites that cause disease and result in death or persistent infection represents a major challenge to global human and animal health. First described in 1901 as Piroplasma equi, this re-emergent apicomplexan parasite was renamed Babesia equi and subsequently Theileria equi, reflecting an uncertain taxonomy. Understanding mechanisms by which apicomplexan parasites evade immune or chemotherapeutic elimination is required for development of effective vaccines or chemotherapeutics. The continued risk of transmission of T. equi from clinically silent, persistently infected equids impedes the goal of returning the U. S. to non-endemic status. Therefore comparative genomic analysis of T. equi was undertaken to: 1) identify genes contributing to immune evasion and persistence in equid hosts, 2) identify genes involved in PBMC infection biology and 3) define the phylogenetic position of T. equi relative to sequenced apicomplexan parasites.ResultsThe known immunodominant proteins, EMA1, 2 and 3 were discovered to belong to a ten member gene family with a mean amino acid identity, in pairwise comparisons, of 39%. Importantly, the amino acid diversity of EMAs is distributed throughout the length of the proteins. Eight of the EMA genes were simultaneously transcribed. As the agents that cause bovine theileriosis infect and transform host cell PBMCs, we confirmed that T. equi infects equine PBMCs, however, there is no evidence of host cell transformation. Indeed, a number of genes identified as potential manipulators of the host cell phenotype are absent from the T. equi genome. Comparative genomic analysis of T. equi revealed the phylogenetic positioning relative to seven apicomplexan parasites using deduced amino acid sequences from 150 genes placed it as a sister taxon to Theileria spp.ConclusionsThe EMA family does not fit the paradigm for classical antigenic variation, and we propose a novel model describing the role of the EMA family in persistence. T. equi has lost the putative genes for host cell transformation, or the genes were acquired by T. parva and T. annulata after divergence from T. equi. Our analysis identified 50 genes that will be useful for definitive phylogenetic classification of T. equi and closely related organisms.

BackgroundEquine piroplasmosis (EP) caused by Theileria equi, Babesia caballi, or both, contributes to significant economic loss in the equine industry and remains uncontrolled in Egypt. This study focuses on surveying T. equi and B. caballi infections and hematological disorders in equine populations in Egypt.MethodsTheileria equi and B. caballi infections were assessed in blood from 88 horses and 51 donkeys in Egypt using light microscopy, indirect immunofluorescent antibody test (IFAT), nested PCR (nPCR), and competitive-ELISA (cELISA) assays. PCR products were examined for specificity by DNA sequencing. Hematological alterations were evaluated using a standard cell counter.ResultsMicroscopic analysis revealed EP infection in 11.4 % and 17.8 % of horses and donkeys respectively. IFAT detected 23.9 % and 17.0 % infection of T. equi and B. caballi, respectively, in horses, and 31.4 % of T. equi and B. caballi in donkeys. T. equi cELISA detected 14.8 % and 23.5 % positive horses and donkeys, respectively, but the B. caballi RAP-1-based cELISA failed to detect any positives, a result hypothesized to be caused by sequence polymorphism found in the rap-1 genes. Nested-PCR analysis identified 36.4 % and 43.1 % positive horses and donkeys, respectively for T. equi and it also identified 19.3 % and 15.7 % positive horses and donkeys, respectively for B. caballi. The overall EP incidence found in the population under study was relatively high and comparable regardless of the diagnostic method used (56.8 % using nPCR and 48.9 % using IFAT). Hematologic analysis revealed macrocytic hypochromic anemia and thrombocytopenia in all piroplasma-infected horses.ConclusionsThe data confirm relatively high levels of EP, likely causing hematological abnormalities in equines in Egypt, and also suggest the need for an improved serological test to diagnose B. caballi infection in this region.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-016-1539-9) contains supplementary material, which is available to authorized users.

No abstract