The relationship between theileria parva parva and t.p. lawrencei as shown by sporozoite antigen and ribosomal RNA gene sequences

[摘要] The aim of this thesis was to develop DNA probes to distinguish between theprotozoan parasites Theileria parva parva and T. p. lawrencei which cause EastCoast fever (ECF) and Corridor disease respectively. ECF was eradicated fromSouth Arrlca in 1954, and today Corridor disease has become the most importantform of theileriosis. Although ECF has been eradicated, the vector ticks are stillprevalent in South Africa and the cattle population would be highly susceptible to arecurrence of the disease, At present there is no reliable means of distinguishingbetween T.p. parva and T. p. lawrencei.Sequence differences between T. parva and other Theileria species have previouslybeen found in the small subunit ribosomal RNA (rRNA) gene; probes designed todetect these sequence differences Can be used to distinguish between Theileriaspecies. We therefore decided to search for differences in the rRNA genes ofT. p. parva and T.p. lawrencei. To this end, the entire RNA transcription unit wasamplified from a cloned T. p, lawrence; parasite; the unit comprises the small subunitrRNA (SSUrRNA) gene, the internal transcribed spacer (ITS) and the large subunitrRNA (LSUrRNA) gene. The amplification products were cloned and sequenced,and the T.p, lawrencei rRNA sequence was compared to that of T. p, parva, Whilethere was little variation in their SSUrRNA and LSUrRNA gene sequences, there wasmajor sequence variation in the ITS The ITSs from twelve T. parva isolates wereamplified, cloned and sequenced, and eleven characterisation oligonucleotide probeswere identified. The T. p, parva isolates screened in this study hybridised with alimited subset of the probes, While the T. p. lawrencei isolates, hybridised with manymore of the probes, indicating that the T. parva population in cattle is morehomogenous than that in buffalo. There thus appears to have been a selection incattle of a relatively homogenous subpopuiation of T. parva from a much larger,more diverse gene pool in buffalo. Although most T.p. parva isolates (93.5%) weredetected by probe TPPI, and most T.p, lawrencei isolates (81.8%) were detected by

[发布机构] University of the Witwatersrand