Analysis of mixed parasite populations ofTheileria sergentiusing cDNA probes encoding a major piroplasm surface protein

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Abstract
SUMMARY: The gene for the 32 kDa surface protein (p32) ofTheileria sergentiwas cloned into λgt11 and its nucleotide sequence was determined. The gene encodes a protein of 283 amino acids as deduced from its nucleotide sequence with a 22 residue N-terminal signal peptide. Using this cDNA as a probe we have isolated another two clones from a cDNA library with a CDM8 vector system derived from the same parasite stock. Comparison with three cDNA clones revealed differential polyadenylation and differences in sequences of non-coding regions. Within the coding regions, there were nucleotide transitions which affected thePstI-restriction site, and one of the transitions was also accompanied by an amino acid substitution (Ala to Gly). Southern blot analysis showed hybridization pattern changes among the parasites isolated from individual calves at different times after infection. From these results, we conclude that at least 3 genetically different parasite populations may coexist, and that transition to predominant parasite populations might occur during persistent infections in a host, possibly to evade the host immune responses.