Comparison of Three Tetracycline Antibiotic Treatment Regimens for Carrier Clearance of Persistent Anaplasma marginale Infection Derived under Field Conditions

Anaplasmosis, caused by the intracellular red blood cell parasite Anaplasma marginale, is the most prevalent tick-transmitted disease of cattle worldwide. Cattle recovering from acute anaplasmosis, including those treated with tetracycline antibiotics, develop lifelong cyclic rickettsemias. Carrier cattle serve as a reservoir of A. marginale for the infection of naive cattle through horizontal, vertical, and iatrogenic transmission. Validated antimicrobial regimens do not exist for eliminating persistent infection; furthermore, anaplasmosis disease control is confounded by the absence of effective vaccines. A diagnostic testing strategy for identification of A. marginale infection and determination of chemotherapeutic success is urgently needed. A novel, real time RTPCR diagnostic assay and oral chlortetracycline (CTC) chemosterilization strategy were developed at Kansas State University under experimental conditions through concurrent RT-PCR results and plasma CTC pharmacokinetic determination. Validation of this diagnostic and treatment strategy utilizing cattle naturally-infected is essential for assembling science-based recommendations for anaplasmosis control, treatment, and eradication.