Subunit vaccines for the control of tick-borne diseases: implications for the future.

Tick-borne parasites are a major constraint to the improvement of livestock productivity in the developing world. These parasites include Theileria parva, T. annulata, Babesia bigemina, B. bovis, Anaplasma marginale and Cowdria ruminantium. The impact of these diseases is currently limited by the use of acaricides to decrease transmission by the tick vectors and immunization of the host animals using live vaccines. The use of acaricide is hampered by the development of acaricide resistance and live vaccines are dependent on cold chain facilities, which are generally unreliable in developing countries. There is therefore a requirement for improved vaccines that circumvent these problems. Candidate vaccine antigens have been identified for most of these parasites and are currently being evaluated for their capacity to induce solid protection.