Antigenic and genotypic relatedness of buffalo-derived Theileria parva from Zambia to cattle-derived parasites and vaccine stocks

Abstract

The African buffalo (Syncerus caffer) is the natural reservoir of Theileria parva, a tick-transmitted protozoan parasite that severely constrains cattle production across eastern, southern, and central Africa. While the antigenic and genetic diversity of cattle-derived T. parva (causing East Coast fever) is well characterized in Zambia, little is known about the buffalo-derived parasites. The latter cause the equally fatal Corridor disease and impact the epidemiology and control of bovine theileriosis, particularly where live vaccines are used. This study investigated antigenic and genotypic diversity of T. parva from three Zambian buffalo populations, in comparison with cattle-derived parasites and vaccine stocks (Katete and Chitongo). Analysis of Tp1 and Tp2 antigen genes revealed contrasting diversity. Tp1 epitopes showed limited variation, whereas Tp2 exhibited extensive polymorphism, especially among buffalo-derived sequences. None of the variations have been previously reported in Zambia, suggesting ongoing diversification. Phylogenetic analysis showed paraphyletic clustering of buffalo and cattle parasites. However, some buffalo genotypes grouped closely with vaccine strains, suggesting potential cross-protection. Only two Tp2 sequences from buffalo-derived parasites clustered with those from cattle or vaccines, highlighting a risk of vaccine break-through. Population genetic analysis using multilocus genotyping demonstrated higher allelic richness and diversity in buffalo-derived parasites compared to cattle-derived. Although buffalo parasites showed greater multiplicity of infection (MOI) and unique alleles, principal coordinate analysis revealed limited genetic sub-structuring and shared alleles across hosts. These results suggest a common ancestry and overlapping transmission cycles. The greater MOI in buffalo populations highlights higher genetic exchange and can complicate control efforts. Overall, the study demonstrates extensive antigenic and genetic diversity of buffalo-derived T. parva in Zambia. These findings have critical implications for current vaccine efficacy, emphasizing the need for continuous molecular surveillance, strict livestock movement control, and vaccine efficacy trials to ensure effective management of T. parva infections.

HIGHLIGHTS • Buffalo are a major reservoir of Theileria parva antigenic and genetic diversity. • Some Zambian buffalo-derived T. parva strains are related to ECF strains. • Buffalo-derived T. parva genotypes shown a distant relationship to vaccine stocks. • Current vaccines may offer limited protection against buffalo-derived T. parva.