Bovine
anaplasmosis, caused by Anaplasma marginale, is an infectious but non-contagious disease. It is spread through
tick bites or by the mechanical transfer of fresh blood from infected to susceptible cattle from biting flies or by blood-contaminated fomites including needles, ear tagging, dehorning and
castration equipment. Transplacental transmission of A. marginale may contribute to the epidemiology of bovine
anaplasmosis in some regions. Bovine
anaplasmosis occurs in tropical and subtropical regions worldwide. Cattle of all ages are susceptible to
infection with A. marginale, but the severity of disease increases with age. Once cattle of any age become infected with A. marginale, they remain persistently infected carriers for life. Diagnosis of bovine
anaplasmosis can be made by demonstration of A. marginale on stained blood smears from clinically infected animals during the acute phase of the disease, but it is not reliable for detecting
infection in pre-symptomatic or carrier animals. In these instances, the
infection is generally diagnosed by serologic demonstration of
antibodies with confirmation by molecular detection methods. The susceptibility of wild ruminants to
infection by A. marginale and the role of wild ruminants in the epidemiology of bovine
anaplasmosis are incompletely known owing to lack of published research, lack of validation of diagnostic tests for these species and cross-reaction of Anaplasma spp.
antibodies in serologic tests. Control measures for bovine
anaplasmosis vary with geographical location and include maintenance of Anaplasma-free herds, vector control, administration of
antibiotics and vaccination.