Molecular epidemiology of Theileria parva in the field

Molecular tools based on seminested RFLP-PCR techniques to characterize fie ld parasites in bloodspots dried on filter paper permitted investigation of the extent and the dynamics of diversity of Theileria parva populations in the field. Parallel molecular studies explored the long-term genome stabil ity of various isolates by probing Southern blots of EcoRI digested total g enomic DNA with four different reference nucleic acid probes. Three polymor phic single copy loci encoding for antigen genes were developed for semines ted PCR detection in order to apply them for a multilocus approach in popul ation genetic studies. Seven alleles were identified for the polymorphic im munodominant molecule (PIM) locus by using restriction enzymes, and 4 allel es each for the p150 and p104 loci. A simple DNA extraction method gave goo d results in amplifying these loci from carrier animals using samples of bl ood dried on filter papers. Results from probing Southern blots of cultures taken at sequential timepoints indicate relative genome stability in T. pa rva in comparison to other parasitic protozoa such as Plasmodium. Comparati vely homogeneous profiles in sympatric isolates from Zambia were identified using all four probes and PCR amplified products which contrasted with the variety found amongst Kenyan stocks. Preliminary characterization of T. pa rva field samples from the Southern Province of Zambia strongly suggest clo nal expansion of one of the components of a non-Zambian trivalent vaccine u sed on a limited scale in the Province from 1985 until 1992.