Bovine babesiosis and anaplasmosis: studies on field performance of live vaccines, diagnostic methods and host responses to infection

• Department of Veterinary Services, Zimbabwe
• Australian Volunteers International, Australia
• Monash University, Australia

About 80% of the world population of 1200 million cattle are at risk from ticks and tick-borne diseases. This project took up the focus of its predecessor (AS2/1991/018) for further study of diseases caused by Babesia species (known as babesiosis) and Anaplasma marginale (known as anaplasmosis). The diseases are often referred to generically as tick fever. Like the malaria pathogens, to which they are related, the parasites spend time in the bloodstream. They are transmitted mainly by blood-sucking ticks of the genus Boophilus, which occurs in many tropical and subtropical regions. Control of the diseases has rested mainly on the practice of dipping cattle in tick-killing chemicals, an expensive procedure that also carries the worry of contamination from the dip chemicals. Vaccination is considered preferable.
ACIAR project AS2/1991/018 made good progress in its aim of improving the methods for diagnosis and control of these diseases in Zimbabwe and Australia. As a result, Zimbabwe can now produce live vaccines to give protection against the two diseases. However, experience in Australia has shown that the vaccines can sometimes give variable results. This could be due to the handling of the vaccine after production and during transport (it must be kept frozen), differences in the way of administering the vaccine to the target cattle at the farm, or differences in the timing and severity of the field infections to which cattle are exposed after vaccination. Also, the effectiveness of the particular strain of parasites used to make the live vaccines may change over time.
Zimbabwe needed to develop effective delivery and monitoring systems for its vaccines. Various unresolved questions about the failure of some vaccines in Queensland and in Zimbabwe also needed investigation. In addition, certain parts of Zimbabwe thought to be free of Babesia had suffered outbreaks and needed further study. The distribution of the parasites could fluctuate considerably in time and space, and a clearer picture of their prevalence would help in assessing the need for vaccination of herds in certain parts of both countries.

The aim of the project was to support Zimbabwe in establishing sustainable methods for the delivery and field monitoring of effective, live vaccines against the two types of tick-borne cattle disease. The work would devise ways of assessing the need for vaccination under the various management conditions in Zimbabwe and Australia, and also address new issues that arose from the research in the earlier project.

Work proceeded on four subprojects. In the first, the best method of delivering frozen vaccines into the countryside in Zimbabwe was investigated. The second collected cattle serum from various locations in Zimbabwe and Australia to test for exposure to the parasites. This information was used to build up a picture of the distribution of the pathogens and determine exactly which species was the predominant cause of 'tick fever' in a locality. This allowed researchers to assess the need for vaccination in different places.
The third component of the work completed the development of a serological test for Babesia bigemina. Exposure to this species has proved difficult to distinguish from exposure to the more common B. bovis, as the antibodies to the two species cross-react. The test was an early priority, and when completed would be used in subproject two.
The final subproject aimed to improve existing methods for assessing the immune responsiveness of cattle and for distinguishing between the different species and strains of Anaplasma.

Zimbabwe's capability for the production of frozen vaccines against the two tick-borne diseases, developed in the earlier project, was enhanced by providing assistance for the country's Central Veterinary Laboratory (CVL) to develop sustainable, effective methods for quality assurance, delivery and field monitoring of the vaccines. The vaccine production section of CVL was developed to the stage of becoming a business unit, which would enable it to fund its activities from vaccine sales.
Full quality assurance procedures and techniques for Babesia and Anaplasma vaccine production have been transferred and applied at CVL. Expertise gained in this area has flowed on to other tick-borne disease vaccine production activities at CVL, thereby increasing sustainability and capacity.
Project scientists prepared a suite of ELISA tests for detecting antibodies to B. bovis, B. bigemina and Anaplasma. They are now in routine use for epidemiological studies to identify the need for vaccination and inform producers in Australia and Zimbabwe, and the tests are also available for institutions in Kenya, Tanzania and Mozambique.
An assay developed during the project extension enables researchers to differentiate between the Australian vaccine strain and African field isolates of B. bigemina. It is being used in Zimbabwe to investigate and confirm reported cases of vaccine failure or severe vaccine reactions.
The development of specific and sensitive techniques for differentiating species and strains of Anaplasma was also completed. An ELISA test to detect the presence of A. centrale has been successfully used to confirm vaccination in vaccine breakdown investigations in Australia. It has also been incorporated as a critical component of the import testing protocol for live Australian cattle destined for Mexico and is currently being evaluated for use in Israel.
Vaccine for local use has always been sold at CVL since the early 1900s. In the last two decades however, the procedures to adjust prices have become too slow to keep up with rising costs. The Agricultural Revolving Fund is now in operation and charges are what can be termed market rates with greater flexibility for price adjustments. Vaccine is priced for both local and export use.
A productive collaborative R&D network linking Australian and African institutions and ILRI developed earlier has been broadened by the addition of more institutions from Australia, Africa, the Philippines and Israel.
An ACIAR/ILRI/ICIPE sponsored workshop was held in April 1999 in Harare to identify and prioritise future tick and tick-borne disease research activities for southern and eastern Africa. One of the highest priorities was to improve existing live vaccines. Consequently a new ACIAR project application (AS2/1999/063) was developed with objectives to improve user friendliness and protection of the vaccines.