Population genetic analysis and sub-structuring in Babesia bovis.

The tick-borne protozoan parasite, Babesia bovis is one of the causes of bovine babesiosis, an economically important disease of cattle in tropical and sub-tropical countries. Using the recently published genome sequence of the parasite, we developed a panel of eight mini- and micro-satellite markers and used these to investigate the role of genetic exchange in the population structure and diversity of the parasite using isolates from Zambia and Turkey. This population genetic analysis showed that genetic exchange occurs and that there are high levels of genetic diversity, with geographical sub-structuring quantified using Wright's F Index. Linkage disequilibrium was observed when isolates from both countries were treated as one population, but when isolates from Zambia were analysed separately linkage equilibrium was observed. The Turkish isolates were sub-structured, containing two genetically distinct sub-groups, both of which appeared to be in linkage equilibrium. The results of the Zambian study suggest that a sub-set of the parasite population is responsible for the westward spread of babesiosis into the previously disease-free central region of the country. The Zambian isolates had a significantly higher number of genotypes per sample than those from Turkey and age was found to be a significant predictor of the multiplicity of infection. The high levels of diversity seen in the Zambian and Turkish B. bovis populations have implications in the development of subunit vaccines against the disease and the spread of drug resistance.