Prevalence of bovine brucellosis and molecular characterization of Brucella abortus virulence genes (omp19 and ure) in western India

Abstract

Bovine brucellosis caused by Brucella abortus remains an endemic zoonosis worldwide, producing substantial economic losses through reproductive failure in dairy cattle and significant public health risks. This study evaluates the prevalence of brucellosis in cattle presenting with a history of abortion from the Pune and Mumbai regions of Maharashtra, India, and characterizes circulating strains using serological, molecular, and phylogenetic approaches. A total of 400 bovine clinical samples (200 milk and 200 blood/serum) were screened using the Milk Ring Test (MRT) and Rose Bengal Plate Test (RBPT). Genus- and virulence-specific conventional Polymerase Chain Reaction (PCR) assays were performed targeting the BCSP31 (223 bp), omp19 (550 bp), and ure (2100 bp) genes. Overall seropositivity was 54.0% (108/200) by MRT and 27.5% (55/200) by RBPT, with consistently higher positivity rates in Pune compared to Mumbai. Molecular screening of 163 seropositive clinical specimens using BCSP31 PCR revealed an overall detection rate of 72.39% (118/163; 78.9% in Pune milk, 66.7% in Pune blood, 61.5% in Mumbai milk, and 50.0% in Mumbai blood). Amplification of virulence markers revealed 27.6% (45/163) positivity for omp19 and 33.7% (55/163) for the urease (ure) gene. Partial gene sequencing and phylogenetic analysis demonstrated high sequence identity of three field-derived isolates (Samples 1, 3, and 4) with the B. abortus S19 reference vaccine strain, whereas Sample 2 clustered distinctly with wild-type field strains. These findings highlight significant endemic exposure, active milk shedding of Brucella, and the coexistence of field and vaccine-related lineages within dairy herds, underlining the necessity for integrated molecular diagnostics and genomic surveillance in regional control programs.