Development of a prophylactic regime using Terramycin/LA to assist in the introduction of susceptible cattle into heartwater endemic areas of Africa

Abstract

As a result of a personal survey in 1982, interviewing veterinarians from Louis Trichardt to Uitenhage, it was concluded that bovine heartwater is currently regarded as the most serious tick-borne disease problem in South Africa. A combination of long-acting oxytetracycline and prednisolone is regarded as the most effective therapy. The disease is almost inevitable in unprotected young high-grade susceptible stock introduced into endemic areas such as the northern Transvaal and the Valley Bushveld of Natal and the Eastern Cape. A series of trials was conducted at Settlers, Pietermaritzburg and East London on farms representative of these areas and it was demonstrated that 4 injections of 20 mg/kg of long-acting oxytetracycline on Days 0, 7, 14 and 21 after introduction enabled such stock to be introduced without the disease occurring. A further trial was carried out on the Pietermaritzburg farm, where it was shown that the number of injections could be reduced to 3, on Days 7, 14 and 21 or Days 7, 12 and 17, or even 2 on Days 7 and 14. Two points need stressing. First, these results were obtained in areas of high heartwater endemicity. Second, in order to be confident that the regime will be effective it is necessary to have acquired knowledge of the epidemiology of the disease at the farm. Thus in the 2nd year at Pietermaritzburg we were able to use a reduced treatment regime because we knew the pattern of disease occurrence. Problems are perceived for the large scale introduction of such a prophylactic regime, namely: (1) a 100% challenge must occur in the first 4 weeks of exposure; (2) immunologically distinct strains of heartwater may occur on the same farm at different times of year; (3) the duration of immunity acquired as a result of the regime has not yet been established, and (4) the attritive Theileria mutans-type pathogen which is very common in South Africa may cause breakdowns in heartwater immunity. Since oxytetracycline is known to be active against all major tick-borne pathogens of cattle, and even apparently against the ticks themselves, some form of prolonged administration of the drug could be used to overcome the problems enumerated above.