Two field trials were carried out in successive years at the Ngong Veterinary Farm, Kenya, in which young cattle, previously unexposed to
tick-borne diseases, were introduced into an area with endemic
East Coast fever while protected by a series of
injections of a long-acting
oxytetracycline. In 1984, 12 animals which received
injections of 20 mg/kg of the
drug on days 0, 7, 14 and 21 after introduction, together with 12 untreated controls, were exposed without tick control until clinical disease occurred. All 12 control animals contracted
East Coast fever by day 24 and 10 of them died. Five of the 12 injected animals had detectable parasites, and one of them required antitheilerial treatment. In 1985, four groups of 10 calves were introduced. One group received
injections of 20 mg/kg of
oxytetracycline on days 7 and 14, one group received
injections on days 7, 14 and 21, and a third group received
injections on days 7, 12 and 17; the fourth group (controls) had no treatment until clinical disease occurred. By day 35 all the control animals had contracted the disease and one had died despite antitheilerial treatment. Three
injections of
oxytetracycline suppressed the disease so that mild reactions occurred in only four animals in each group, but two
injections failed to prevent severe reactions in two animals and mild reactions in four others.(ABSTRACT TRUNCATED AT 250 WORDS)