Emergence of new types of Theileria orientalis in Australian cattle and possible cause of theileriosis outbreaks.

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.

Viability assays of intra-erythrocytic organisms using fluorescent dyes.

Three intra-erythrocytic tick fever organisms of cattle (Babesia bovis, Babesia bigemina and Anaplasma centrale) were subjected to a range of stressors, including heat, storage over time, specific chemotherapy and cryopreservation. Various stains, both alone and in combination, were used in an attempt to assess viability of these organisms before and after the stressors were applied. Carboxyfluorescein diacetate succinimidyl ester (CFSE) stained live Babesia spp. very well while fluorescein diacetate (FDA) stained A. centrale successfully. Propidium iodide (PI) and ethidium-homodimer-1 (Eth-D) were used as counter stains to identify dead organisms. Stain combinations allowed differentiation between living and dead Babesia organisms after exposure to heat and after chemotherapy. PI and Eth-D as counter stains were of little value after deglycerolisation of cryopreserved organisms. Possible reasons for this limited success in determining death or viability of tick fever organisms after some treatments include the impermeability of red blood cells to PI and Eth-D counter stains or the loss of live and/or dead organisms during sample processing.

Attenuated vaccines for tropical theileriosis, babesiosis and heartwater: the continuing necessity.

Overwhelming evidence has accumulated of the effectiveness of immunization with live attenuated vaccines to control tick-borne diseases of livestock. Despite several disadvantages, vaccination with live attenuated organisms against tropical theileriosis, babesiosis and possibly heartwater constitutes one of the most cost-effective intervention strategies. Although great advances have been made through genomics and proteomics research, this has not yet translated into effective non-living vaccines. As a result, there is a continuing necessity to use available live vaccines in tick and tick-borne disease-control strategies adapted to conditions prevailing in many parts of the world.