Elimination of naturally acquired chronic Anaplasma marginale infections with a long-acting oxytetracycline injectable.

Four injections of a long-acting oxytetracycline (20 mg/kg) were administered at 3-day intervals to 14 naturally infected anaplasmosis carrier cattle. Individual anaplasma serology titers were evaluated, using complement-fixation and rapid card-agglutination tests at frequent intervals during a 180-day posttreatment period. Serologic results indicated fluctuating complement-fixation titers during the trial period. However, at trial termination, 12 of 14 animals were negative by complement-fixation testing and all animals were card-test negative. Eight splenectomized calves given 10 ml of blood from the medicated cows at their posttreatment day 150 failed to manifest any clinical, hematologic, or serologic signs of anaplasmosis during 56 days. Susceptibility to anaplasmosis challenge exposure was demonstrated by positive clinical and serotest reactions when 3 of the recipient calves were inoculated with blood from a parasitemic carrier calf.