Reduction in mortality from heartwater in cattle, sheep and goats exposed to field challenge using an inactivated vaccine

Inactivated vaccines for heartwater prepared with the commercially acceptab le Montanide ISA 50 (ISA 50) adjuvant were field tested in Beer goats in Bo tswana, Angora goats in South Africa, and Merino sheep in Zambia and Zimbab we. Two vaccines, one made using the Zimbabwean Mbizi isolate and the other using the respective local field isolate (Sunnyside in Botswana; Bathurst in South Africa; Lutale in Zambia), were tested at each site, except in Zim babwe where only the Mbizi vaccine was tested. Compared with unvaccinated a nimals, the Mbizi vaccine significantly protected goats and sheep against f ield Amblyomma tick challenge in Botswana, Zambia and Zimbabwe (P = 0.018, 0.002 and 0.017, respectively), but failed to protect Angora goats in South Africa. However, in South Africa the vaccine prepared using the local fiel d isolate Bathurst, induced significant protection (P = 0.008). The vaccine s containing the local isolates at all other sites were less protective tha n the Mbizi vaccine. The Mbizi inactivated vaccine also significantly prote cted 17 of 21 cattle (P = 0.05) against heartwater challenge from held tick s in Zimbabwe. Against the same challenge only 7 of 21 unvaccinated control cattle survived. This study demonstrates that heartwater is a major constraint to upgrading livestock in endemic areas, and caused an overall mortality of 77.6% in nai ve sheep and goats (97 of 125 died) and 67% in cattle (14 of 21 died). In c ontrast, the vaccine had a protective effect by reducing the overall mortal ity in sheep and goats to 54.3% (113 of 208 died) and to 19% in cattle (4 o f 21 died). (C) 2001 Published by Elsevier Science B.V.