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.
Clinical relevance: Our study was the first to report prevalence estimates for bovine anaplasmosis in Ohio. Although prevalence was higher than other states, this is most likely due to our sampling approach. Our results suggested that older animals are more likely to be infected with A marginale, and when animals are instead infected with A phagocytophilum, serology alone can be misleading wherever the 2 species co-occur. Our study can guide wider epidemiological studies for informing management in Ohio.