Brucella melitensis in Iranian Dairy Cattle: Isolation, Molecular Identification, and Biotyping

Background: Brucellosis, caused by Brucella species, remains a significant zoonotic and economic challenge in Iran, where Brucella melitensis is increasingly detected in dairy cattle due to close contact with infected sheep and goats. The persistence of B. melitensis highlights the limitations of existing control strategies and the need for improved approaches. Investigating B. melitensis in Iranian dairy cows is crucial due to their interaction with mixed sheep and goat populations. Methods: In 2021, 73 lymphoid tissue samples were collected from reactor-positive cows in seven Iranian provinces. Samples were analyzed using traditional bacteriological methods, biotyping, and molecular tools such as AMOS-PCR and Bruce-ladder PCR for strain identification and characterization. Samples were collected from seven provinces in Iran, namely Tehran, Kerman, Isfahan, Alborz, Qazvin, West Azerbaijan, and Fars. Results: Out of 73 lymph node samples collected from seven Iranian provinces, 15 (20.55%) tested positive for B. melitensis through culture and PCR. Culture results confirmed uniform growth conditions with no significant differences among provinces. Molecular analysis validated the identity of all isolates, with AMOS-PCR amplifying a 731 bp product and Bruce-ladder PCR confirming field strains through species-specific DNA fragments. Biotyping revealed that 14 isolates were B. melitensis Biotype 1, distributed across six provinces, while one isolate from Kerman Province was Biotype 3. Conclusion: The prevalence of B. melitensis in Iranian dairy cattle highlights significant gaps in existing vaccination programs and the urgent need for cross-species protective vaccines. Given its zoonotic risks and public health impact, enhanced surveillance, advanced diagnostics, and region- specific strategies are critical for effective control.The RB51 vaccine has notable limitations, including its inability to protect against B. melitensis, lack of standardized protocols, and failure to aid in brucellosis eradication. Collaboration among public health authorities, veterinarians, and policymakers is critical to address these challenges and mitigate the spread of B. melitensis in Iran.