Bovine Brucellosis: First Comprehensive Evaluation from Hamedan, an Endemic Area in Iran

Brucellosis is an infectious zoonotic disease. The disease is one of the major concerns in developing societies due to its great importance for public health and economic losses in the animal industry. The principal target of the study was to detect the prevalence of brucellosis and associated risk factors in cattle from Hamedan (western Iran) using different laboratory techniques. In 2020, blood samples from 900 cattle were obtained to detect brucellosis prevalence in the region. After screening by the modified Rose Bengal plate test, the positive samples were reevaluated using the Wright standard tube agglutination test (SAT), 2-Mercaptoethanol (2-ME), and Enzyme-linked immunosorbent assay. Serology-positive samples were confirmed by culturing bacteria from the lymph nodes and detecting Brucella DNA using specific primers, the BCSP31 target gene, and the IS711 locus. Brucellosis was detected in 1.88% (17/900, 95% CI 1-2.76%) of animals. The high prevalence of brucellosis was observed in female animals (2.77%, p = 0.947), 2-4 years old animals (2.88%, p = 0.994), Holsteins (5.69%, p = 0.989), farm animals (6.49%, p = 0.999), and animals with a history of vaccination against brucellosis (3.04%, p = 0.915). In addition, there was no positive sample in October and December, and also the highest prevalence rate was found in September (5.33%, p = 0.970). There was no statistically significant relationship between the variables and the rate of brucellosis. There were similar results between the different applied laboratory methods. The minimum and maximum levels of titer in the SAT method were + 2/80 and + 2/320, respectively. The rates for 2-ME were + 2/40 and + 4/160. Out of 17 positive samples, 2 were confirmed for B. melitensis and 15 for B. abortus. Notably, no sample showed co-infection of both B. abortus and B. melitensis. This study represents the first comprehensive evaluation of cattle brucellosis in Hamedan. Through molecular evaluation, the presence of Brucella spp. was identified in the seropositive samples. Among the cattle samples, the primary species isolated and confirmed was B. abortus. This finding shed light on the prevalence and distribution of Brucella species in the region, providing crucial insights for future disease management and control efforts. Considering the specificity of the used genes to detect bacteria, molecular biology can be a safe and rapid technique for diagnosing brucellosis, especially in cases without conclusive results. Regular screening of animals and culling seropositive animals are highly recommended; these affect the control of disease at the herd level.