The objectives of the study were: 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.
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.
Overall, four beef cattle herds (n = 327) were sampled between December 2020 and December 2021.
The authors 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, two animals tested positive for A phagocytophilum.
The authors confirm that this was the first paper to report prevalence estimates for bovine anaplasmosis in Ohio. Although prevalence was higher than other states, this is most likely due to sampling approach.
The 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. In conclusion, this study can guide wider epidemiological studies for informing cattle management in Ohio.
Andreas Eleftheriou, DaZané Cole, Justin Kieffer and Risa Pesapane. “Molecular prevalence of Anaplasma marginale and associated risk factors in beef cattle herds from Ohio: a cross-sectional study.” J Am Vet Med Assoc. 2022 Sep 1;1-5. doi: 10.2460/javma.22.05.0204.