The relationship between theileria parva parva and t.p. lawrencei as shown by sporozoite antigen and ribosomal RNA gene sequences
Date
1997
Authors
Collins, Nicola, Elaine
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Abstract
The aim of this thesis was to develop DNA probes to distinguish between the
protozoan parasites Theileria parva parva and T. p. lawrencei which cause East
Coast fever (ECF) and Corridor disease respectively. ECF was eradicated from
South Arrlca in 1954, and today Corridor disease has become the most important
form of theileriosis. Although ECF has been eradicated, the vector ticks are still
prevalent in South Africa and the cattle population would be highly susceptible to a
recurrence of the disease, At present there is no reliable means of distinguishing
between T.p. parva and T. p. lawrencei.
Sequence differences between T. parva and other Theileria species have previously
been found in the small subunit ribosomal RNA (rRNA) gene; probes designed to
detect these sequence differences Can be used to distinguish between Theileria
species. We therefore decided to search for differences in the rRNA genes of
T. p. parva and T.p. lawrencei. To this end, the entire "RNA transcription unit was
amplified from a cloned T. p, lawrence; parasite; the unit comprises the small subunit
rRNA (SSUrRNA) gene, the internal transcribed spacer (ITS) and the large subunit
rRNA (LSUrRNA) gene. The amplification products were cloned and sequenced,
and the T.p, lawrencei rRNA sequence was compared to that of T. p, parva, While
there was little variation in their SSUrRNA and LSUrRNA gene sequences, there was
major sequence variation in the ITS The ITSs from twelve T. parva isolates were
amplified, cloned and sequenced, and eleven characterisation oligonucleotide probes
were identified. The T. p, parva isolates screened in this study hybridised with a
limited subset of the probes, While the T. p. lawrencei isolates, hybridised with many
more of the probes, indicating that the T. parva population in cattle is more
homogenous than that in buffalo. There thus appears to have been a selection in
cattle 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%) were
detected by probe TPPI, and most T.p, lawrencei isolates (81.8%) were detected by
Description
A thesis submitted to the Faculty of Science,
University of the Witwatersrand, Johannesburg,
in fulfillment of the requirements for the degree
of Doctor of Philosophy.
Keywords
Theileria parva -- South Africa., Theileriosis.