Improved methods for the diagnosis and control of bovine babesiosis and anaplasmosis in Zimbabwe and Australia

• Veterinary Research Laboratory, Zimbabwe

Bovine babesiosis and anaplasmosis are economically important tick-borne parasitic blood diseases common to Australia, Africa and other tropical and sub-tropical countries. Although the diseases have been largely controlled in Sub-Saharan Africa by frequent (approximately weekly) use of acaricides, this practice is undesirable on economic and environmental grounds.

A preferred strategy is to combine less frequent (strategic) use of acaricides with vaccination against the blood parasites and selection of tick-resistant cattle. The latter approach has been applied with reasonable success in northern Australia for 15-20 years.

It has also been introduced in several countries in eastern and southern Africa, but is hindered in some areas because of a lack of effective vaccines. Zimbabwe is currently phasing in a policy of strategic dipping and is keen to ensure vaccines are available to prevent substantial losses from babesiosis, anaplasmosis and other diseases.

Two years ago the Queensland Department of Primary Industries' Tick Fever Research Centre (TFRC) provided the parasite strains (Babesia bovis, B. bigemina and Anaplasma centrale) now being used to prepare vaccines in Malawi. In turn, Malawi recently provided Zimbabwe with the Australian vaccine strains of Babesia (K strain, B. bovis; G strain, B. bigemina).

Recently the K strain of B. bovis, used in Australia for 10 years, apparently lost efficacy on many cattle properties, resulting in several outbreaks of disease. This strain has been replaced in Australia, but is still used in Malawi and is being held in frozen storage as a potential vaccine strain in Zimbabwe. The T strain of B. bovis replaced the K strain as vaccine in Australia but it too is now failing. Finding reasons for vaccine failure, ways of preventing it and better diagnostic tests are high priorities for research in Australia.

The general approach in this project is to complement existing activities by integrating with and expanding current tick-borne disease projects in African countries, Zimbabwe in particular. Objectives are to:

. assist Zimbabwe in developing protocols for the production and distribution of effective, live vaccines against bovine babesiosis and anaplasmosis;

. collaborate in the design and implementation of field and laboratory studies to establish the purity and efficacy of the vaccines produced in Zimbabwe;

. provide Zimbabwe with expertise to culture Babesia in vitro;

. develop better methods for differentiating species and strains of Babesia and apply these methods in problem-solving research in Australia and Africa; and

. develop a better diagnostic test for Anaplasma marginale than the present card agglutination test.

The research methods are a mixture of applied research, strategic research and technology transfer, and vary in proportion with each objective. Exchange visits by project staff will allow detailed planning of facilities and implementation of procedures required to produce vaccines at the Veterinary Research Laboratory in Zimbabwe, based on the TFRC production system, but modified where necessary. Vaccines will be tested for efficacy in field trials on commercial properties in Zimbabwe, where more susceptible
(Bos taurus) cattle are concentrated. Testing will be dependent on natural challenge.

In addition, isolated field strains of blood parasites will be used as challenge strains in the laboratory, added to the bank of parasite strains available for studies on marker techniques and serological tests, and compared between countries.

The project will facilitate and expand the collaborative approach to solving problems with tick-borne diseases. Benefits first felt in Australia and Zimbabwe will spread with wider adoption of strategic dipping in Africa. Zimbabwe will receive effective vaccines against babesiosis and anaplasmosis. In Australia, improved diagnostic tests will facilitate the cattle export trade, and, in the longer term, increased knowledge of vaccine and field strains of Babesia will provide the basis for improved vaccines and disease control strategies.

Superior diagnostic tests will be developed at TFRC, involving identification of genotypic markers for different parasite strains and the development (or acquisition) of monoclonal antibodies. The latter will involve collaboration with scientists at the International Laboratory for Research on Animal Diseases (ILRAD) in Kenya, who have produced capture ELISAs and monoclonal antibodies for each parasite and are keen to have these assessed against Australian parasites.