Assess the efficacy of Buparvaquone for the treatment of bovine theileriosis

Summary

Theileria is a common, usually benign, blood parasite of cattle in eastern Australia. However, outbreaks of clinical disease have recently been observed, usually associated with cattle movements to new areas. Mortality rates have been reported to be as high as 30%. This clinical disease has been given the name benign theileriosis to distinguish it from the more pathogenic theilerioses (East Coast fever and tropical theileriosis) overseas. It appears there are three different variants (Ikeda, Chitose and Buffeli) of this benign Theileria sp. There are currently no drugs registered to treat cattle infected with the benign Theileria sp., leaving producers and veterinarians with a hopeless situation during these clinical outbreaks.  A working group, established to investigate this recent increase in clinical disease, emphasised the need to find a suitable therapeutic agent. Buparvaquone is registered in about 20 countries for the treatment of East Coast fever and tropical theileriosis. Due to the small potential market in Australia, it is not economically feasible to register the drug here. However, it is worth applying to the Australian Pesticides and Veterinary Medicines Authority (APVMA) for a minor use permit in order to make buparvaquone available in this country. The objective of this project was to do the Australian dose confirmation trials as outlined in the Manual of Requirements and Guidelines of the Australian Pesticides and Veterinary Medicines Authority (APVMA) to obtain such a permit. As part of this, the collection of isolates of the different variants of benign Theileria spp was required. Several isolates of local Theileria sp were collected and tested to determine their type.
​A pure Ikeda variant was collected, as well as a number of mixed-variant isolates. Pure Chitose or Buffeli isolates were not identified. The efficacy study used splenectomised calves to demonstrate the anti-parasitic activity of the drug. Two groups of calves were inoculated with a mixed-variant isolate and a pure Ikeda isolate. Half of each group was treated with buparvaquone at the dose rate used for the pathogenic theilerioses (2.5mg/kg), and the other half were left as untreated controls. The treated calves in both groups had dramatic reductions in parasitaemia (89-95% reduction) by day 4 after treatment whereas the parasitaemia in the untreated controls increased over the same period. It was confirmed that buparvaquone was indeed a very effective drug against this parasite. A minor use permit to enable its use in clinical outbreaks should be pursued as a matter of urgency so that veterinarians dealing with outbreaks will be able to treat cattle with a specific anti-Theileria drug. Once a minor use permit is approved, further work will need to be done to show its effect in clinically affected animals. This will need to be done as field trials during naturally occurring outbreaks since it is difficult to replicate this disease situation due to the usually benign nature of this parasite. Additional work (such as tissue residue depletion studies) may need to be done if buparvaquone is to be fully registered in the future. Although a relatively minor disease on an industry-wide basis, it is hoped that the availability of an effective drug like buparvaquone will have a very significant benefit for those producers who do face an outbreak of clinical benign theileriosis in the future.