| dc.description.abstract | Theileria parasites cause a benign infection of cattle in parts of Australia where they are endemic, but have, in
recent years, been suspected of being responsible for a number of outbreaks of disease in cattle near the coast of
New South Wales. The objective of this study was to identify and characterize the species of Theileria in cattle on
six farms in New South Wales where disease outbreaks have occurred, and compare with Theileria from three
disease-free farms in Queensland that is endemic for Theileria. Special reference was made to sub-typing of
T. orientalis by type-specific PCR and sequencing of the small subunit (SSU) rRNA gene, and sequence analysis of
the gene encoding a polymorphic merozoite/piroplasm surface protein (MPSP) that may be under immune
selection. Nucleotide sequencing of SSU rRNA and MPSP genes revealed the presence of four Theileria genotypes:
T. orientalis (buffeli), T. orientalis (ikeda), T. orientalis (chitose) and T. orientalis type 4 (MPSP) or type C (SSU rRNA).
The majority of animals showed mixed infections while a few showed single infection. When MPSP nucleotide
sequences were translated into amino acids, base transition did not change amino acid composition of the protein
product, suggesting possible silent polymorphism. The occurrence of ikeda and type 4 (type C) previously not
reported to occur and silent mutation is thought to have enhanced parasite evasion of the host immune response
causing the outbreak. | en |
