Factors associated with seroconversion to the major piroplasm surface protein of the bovine haemoparasite Theileria orientalis.

Cheryl Jenkins,Daniel R Bogema

doi:10.1186/s13071-016-1395-7

Abstract

BackgroundBovine theileriosis caused by Theileria orientalis is an emerging disease of cattle in the Asia-Pacific region where it causes a significant economic burden to meat and milk production. While host immunological responses to the lymphocyte-transforming species of Theileria, T. parva and T. annulata, have been well studied, little is known about the immune response to this non-transforming species.MethodsWe developed a recombinant antigen ELISA based on the major piroplasm surface protein (MPSP) of T. orientalis and investigated whether seroconversion to the MPSP was associated with clinical factors (anaemia), parasite burden and parasite genotype. We also examined the dynamics of seroconversion in animals acutely infected with T. orientalis.ResultsIn cattle testing qPCR positive for T. orientalis, seroconversion was more frequent in anaemic compared to normal cattle (P < 0.0001). The ELISA ratio (ER) was highly correlated with total parasite burden as measured by qPCR (r = 0.69; P < 0.0001); however when loads of individual genotypes of the parasite were examined, only the pathogenic Ikeda genotype was highly correlated with ER. Conversely, seroconversion was less frequently detected in the presence of benign T. orientalis genotypes. Temporal measurement of the serological response, parasite burden and packed cell volume (PCV) in acutely infected animals revealed that seroconversion to the MPSP occurs within 2-3 weeks of the initial qPCR detection of the parasite and coincides with a peak in infection intensity and a declining PCV.ConclusionWhether the serological response to the MPSP is immunoprotective against re-infection or recrudescence requires further investigation; however the MPSP represents a promising target for a subunit vaccine given that genetic variability within the MPSP results in differential pathogenicity of T. orientalis.

Highlights

Bovine theileriosis caused by Theileria orientalis is an emerging disease of cattle in the Asia-Pacific region where it causes a significant economic burden to meat and milk production
Immunological cross-reactivity between genotype major piroplasm surface protein (MPSP) While the MPSP gene is the most commonly used marker to discriminate between the various T. orientalis genotypes, the proteins encoded by these genes display a high degree of sequence conservation
Some variability in the reactivity of serum in detecting their specific targets was observed based on the intensity of the bands detected (Fig. 1); the MPSP antigens were pooled for subsequent use in the ELISA assay

Summary

Introduction

Bovine theileriosis caused by Theileria orientalis is an emerging disease of cattle in the Asia-Pacific region where it causes a significant economic burden to meat and milk production. Theileria orientalis is an emerging apicomplexan pathogen of cattle in the Asia-Pacific region. Many recent studies have focussed on identification and differentiation of various genotypes of T. orientalis. These genotypes are defined based on sequence variations in the gene encoding the major piroplasm surface protein (MPSP), an immunodominant antigen expressed during both sporozoite and piroplasm phases of the T. orientalis life-cycle [4]. While eleven genotypes of T. orientalis have been identified globally (Types 1-8 and N1-N3) [5], disease outbreaks in cattle have been largely limited to Type

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Conclusion