Abstract
BackgroundEast Coast fever (ECF) caused by Theileria parva is endemic in Rwanda. In this study, the antigenic and genetic diversity of T. parva coupled with immunization and field challenge were undertaken to provide evidence for the introduction of ECF immunization in Rwanda.MethodsBlood collected from cattle in the field was screened for T. parva using ELISA and PCR targeting the p104 gene. Tp1 and Tp2 gene sequences were generated from field samples and from Gikongoro and Nyakizu isolates. Furthermore, multilocus genotype data was generated using 5 satellite markers and an immunization challenge trial under field conditions using Muguga cocktail vaccine undertaken.ResultsOut of 120 samples, 44 and 20 were positive on ELISA and PCR, respectively. Antigenic diversity of the Tp1 and Tp2 gene sequences revealed an abundance of Muguga, Kiambu and Serengeti epitopes in the samples. A further three clusters were observed on both Tp1 and Tp2 phylogenetic trees; two clusters comprising of field samples and vaccine isolates and the third cluster comprising exclusively of Rwanda samples. Both antigens exhibited purifying selection with no positive selection sites. In addition, satellite marker analysis revealed that field samples possessed both shared alleles with Muguga cocktail on all loci and also a higher proportion of unique alleles. The Muguga cocktail (Muguga, Kiambu and Serengeti) genotype compared to other vaccine isolates, was the most represented in the field samples. Further low genetic sub-structuring (FST = 0.037) coupled with linkage disequilibrium between Muguga cocktail and the field samples was observed. Using the above data to guide a field immunization challenge trial comprising 41 immunized and 40 control animals resulted in 85% seroconversion in the immunized animals and an efficacy of vaccination of 81.7%, implying high protection against ECF.ConclusionsAntigenic and genetic diversity analysis of T. parva facilitated the use of Muguga cocktail vaccine in field conditions. A protection level of 81.7% was achieved, demonstrating the importance of combining molecular tools with field trials to establish the suitability of implementation of immunization campaigns. Based on the information in this study, Muguga cocktail immunization in Rwanda has a potential to produce desirable results.
Highlights
East Coast fever (ECF) caused by Theileria parva is endemic in Rwanda
East Coast fever (ECF) is a disease of cattle caused by Theileria parva, a protozoan parasite that is transmitted by the three-host tick Rhipicephalus appendiculatus [1]
In contrast to other studies [25, 28, 29, 51, 52], we extensively investigated the extent of sequence diversity, phylogenetic relationships and evolutionary dynamics of Tp1 and Tp2 genes coupled with satellite analysis using a panel of five satellite markers to determine the similarities among the field samples collected from Bugesera
Summary
East Coast fever (ECF) caused by Theileria parva is endemic in Rwanda. East Coast fever (ECF) is a disease of cattle caused by Theileria parva, a protozoan parasite that is transmitted by the three-host tick Rhipicephalus appendiculatus [1]. Central and southern Africa, ECF is considered to be the most economically important tick-borne disease of cattle [2] accounting for almost half of the deaths in calves in endemic countries and causing losses of up to 1 million cattle and US$300 million in revenue annually [3]. The disease is associated with high levels of mortality, especially in improved stocks and indigenous cattle in endemically unstable areas [4], it is a major constraint to increasing livestock production through adoption of genetically improved breeds of cattle. Breed improvement programmes in Rwanda are hampered by protozoan tick-borne parasites especially ECF [7,8,9] which has a prevalence of more than 80% [10, 11]
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