Therapeutic efficacy of combined oxytetracycline and streptomycin with benzylpenicillinin naturally Brucella-infected dairy cross-bred cows in Bangladesh

Background: Brucellosis is an important infectious zoonotic disease caused by bacteria of the genus Brucella. It has global significance due to its adverse effects on public health, economics, and trade of animals and animal products. The causative agents of brucellosis, which have no plasmids or toxins and show distinctive virulence, are most significantly represented by intracellular survival. The commonly used antimicrobial drugs are not capable of entering the Brucella-infected cells that are safe from antibiotic treatment, but such treatments are only effective in the bacteremia phase of infection. Reports on the therapeutic management and cure of bovine brucellosis are limited in the literature. Therefore, an attempt was made to evaluate the combined oxytetracycline and streptomycin with benzylpenicillin injections in naturally Brucella-infected high-yielding dairy cross-breed cows. Objectives: This study was conducted to determine the sero-molecular prevalence and therapeutic responses of combined oxytetracycline and streptomycin with benzylpenicillin in naturally Brucella-infected dairy cross-bred cows. Materials and Methods: Serum samples of 460 (290 from Central Cattle Breeding and Dairy Farm, 170 from Military Dairy Farm, Savar, Dhaka) lactating cross-bred cows along with their milk samples were collected randomly. Serum samples were screened for brucellosis with the Rapid Antigen Kit Test, Rose Bengal Test (RBT), and Milk ring test (MRT), and positive samples were tested further with PCR for confirmatory diagnosis. Out of 11 all tests positive cows, of which three had a history of abortion were selected for therapeutic trials with combined long-acting oxytetracycline @ 25 mg/kg BW 3 doses at 24-hour intervals via intrauterine injection and streptomycin @ 20 mg/kg BW with benzylpenicillin @ 40,000 IU/kg 5 doses at 24 hours interval via intramuscular injections. Blood samples of all the Brucella-negative control and pre- and post-treatment stages of all the Brucella-infected cows were tested for Brucella by using PCR. Results: Out of 460 randomly collected serum samples, 18 serum samples 3.9% (95% CI 2.4-6.2) were found positive using RBT and Rapid Antigen Kit Test and 13 of the samples 2.8% (CI 1.5-4.9) were positive respectively. The overall seroprevalence was found to be 3.9% (95% CI 2.4-6.2) using RBT and Rapid Antigen Kit Test and 2.8% (CI 1.5-4.9) using Milk Ring Test, respectively. The odds of brucellosis were 7.4 times (95% CI: 2.5-21.5) higher in cows with repeat breeding than those without repeat breeding. Moreover, the seroprevalence of brucellosis was significantly higher (Odds ratio: 15.7; 95% CI: 5.2-47.4) in cows with retention of fetal membranes than without retention of fetal membranes. Base pair PCR 602. However, of the three treated cows, three became pregnant on artificial insemination with a normal reproductive cycle which needs to explore its status in further research. Conclusions: Combined antibiotic with oxytetracycline (I/U) and streptomycin with benzylpenicillin (I/M) against clinical Brucella infection showed some encouraging results and can be implemented at the field level.