Sero-molecular epidemiology and rick factors analysis of brucellosis in human and lactating cows of military dairy farms in Bangladesh

Background: Brucellosis is a neglected re-emerging important zoonotic disease in the developing world. Most of the research on brucellosis was limited on the sero-epidemiology during the last 50 years and recently molecular techniques have been initiated to study brucellosis in Bangladesh. Objectives: The objectives of this study were to determine sero-molecular prevalence, identify risk factors and detect Brucella species associated with bovine and human brucellosis in Bangladesh Materials and Methods: Serum and milk samples from 1003 lactating dairy cows of eight military dairy farms and 715 serum samples of dairy farm workers and hospital patients were collected during the 36 months period from 2017 to 2020. All the collected sera and milk samples were tested with four different commercial diagnostic test kits to detect the prevalence of Brucella infection. The four sero-positive milkers sera and milk, and all animal samples collected from aborted cases were tested for Brucella genus-specific RT-PCR and Brucella species-specific DNA (B. abortus and B. melitensis) Multiplex PCR. Conventional PCR and sequencing were also performed. Univariable and multivariable logistic regression were used to identify important risk factors of brucellosis. Results: The overall 2.39% sero-prevalence of Brucella infection was recorded with all the CFT, SAT and ELISA assay and 3.09% with RBT, whereas only 0.20% tested milks samples showed positive with MRT in the lactating dairy cows. The B. abortus DNA was amplified from all of the four RBT positive human serum samples tested. Phylogenetic tree of partial 16S ribosomal RNA sequences of the PCR products was closely matched with B. abortus. Three variables (age, parity and abortion) were found to be significantly associated with B. abortus infection in lactating cows. Conclusions: B. abortus is the causal agent of bovine brucellosis which is identified as the first time as an etiological agent of human brucellosis in occupationally exposed dairy farm workers in Bangladesh. This study could not detect the most important zoonotic B. melitensis DNA either in humans or animal samples, even in any earlier studies and therefore, further studies are required to explore the occurrence of B. melitensis in human and animal population in Bangladesh.