Current challenges in the diagnosis and control of bovine anaplasmosis

Abstract

Bovine anaplasmosis, caused by the intracellular rickettsia Anaplasma marginale, continues to impact cattle production in the US. Control and management of bovine anaplasmosis is influenced by our understanding of the complexity of this pathogen, interactions with both cattle and tick hosts, and the disease. A. marginale is maintained in nature through biological transmission by ticks and mechanical transmission by any means of blood transfer from infected to susceptible cattle. The major surface protein 5 (MSP5)-based cELISA, approved for use in the US and Canada, has proven to be a sensitive serologic test. However, more recently this test has been shown to be cross-reactive with closely related organisms, including A. phagocytophilum, because of the conservation of MSP5. Therefore, additional molecular tests may be required in some situations to confirm the identity of the infective agent. While tetracycline antimicrobials are approved by the US Food and Drug Administration for prevention or treatment of acute anaplasmosis, no antimicrobials are labeled for elimination of persistent A. marginale infection. Administration of tetracyclines is an important means of preventing clinical anaplasmosis, but does not prevent cattle from becoming infected with A. marginale. The mode of action of tetracycline is bacteriostatic rather than bactericidal, and its long-term use does not consistently clear cattle of persistent A. marginale infections. USDA approved vaccines for anaplasmosis are currently unavailable. The challenges of vaccine development include the antigenic variation of A. marginale that occurs during persistent infections and the increased antigenic diversity of A. marginale strains, especially in areas of ongoing cattle movement. The overall goal of this and a previous overview is to summarize the current status of knowledge and research on bovine anaplasmosis, and to provide veterinarians with answers to frequently asked questions.