OBJECTIVE To estimate the prevalence of Anaplasma marginale, the causative agent of bovine anaplasmosis, in beef herds from Ohio; evaluate farm identity and animal age as risk factors; and examine serologic cross-reactivity with Anaplasma phagocytophilum, an emerging disease agent. ANIMALS 4 beef cattle herds (n = 327) sampled between December 2020 and December 2021. PROCEDURES To address the broader investigation of characterizing Anaplasma spp and genotypes in Ohio, herds with a history of clinical anaplasmosis were targeted. Blood was screened for antibodies to Anaplasma spp using a competitive enzyme-linked immunosorbent assay with seropositive samples tested for A marginale using real-time PCR. If negative, samples were also tested for A phagocytophilum. RESULTS We estimated a statewide molecular prevalence of 38.53 (95 CI, 33.26 to 43.81), with some farms exhibiting higher prevalence than others (19.40 to 56.86). Accounting for farm identity, the odds of an animal becoming infected increased by 1.41 (95 CI, 1.28 to 1.58) for every year in age. Forty-four animals tested seropositive but PCR negative for A marginale. Out of these, 2 tested positive for A phagocytophilum.
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