Molecular and serological detection of Anaplasma marginale indicates widespread exposure among crossbred cattle in Karnal (Haryana), India.

Bovine anaplasmosis, caused by the tick-borne rickettsial pathogen Anaplasma marginale, is a major constraint to cattle health and productivity in tropical and subtropical regions. The present study aimed to investigate the molecular and serological prevalence of A. marginale infection in crossbred cattle from Karnal (Haryana), India, using complementary serological and molecular diagnostic approaches. A total of 150 blood samples were collected from adult female crossbred cattle maintained under different management systems, including organized farms, gaushalas, and field conditions. Serum samples were screened for antibodies against A. marginale using a competitive enzyme-linked immunosorbent assay (cELISA) based on the major surface protein 5 (MSP5) antigen, while genomic DNA extracted from whole blood was analyzed by polymerase chain reaction (PCR) targeting the MSP5 gene of A. marginale. Representative PCR amplicons were confirmed by Sanger sequencing. Serological screening revealed a high overall seroprevalence of 92.7% (139/150), indicating widespread exposure to A. marginale among the sampled cattle. In contrast, PCR detected A. marginale DNA in 76.0% (114/150) of the animals. The higher detection rate by cELISA compared with PCR likely reflects persistent antibody responses following previous exposure or infection, whereas PCR identifies animals with detectable bacteremia at the time of sampling. These findings demonstrate a high serological and molecular detection rate of A. marginale among crossbred cattle in the sampled population of Karnal district. The study highlights the value of integrating serological and molecular diagnostic approaches for epidemiological surveillance of bovine anaplasmosis and underscores the importance of effective tick control and routine monitoring to reduce the disease burden in dairy cattle.