Epidemiology Aspects of Brucella-DNA Detection Using Real-time PCR from Bovine Whole Blood Samples in Colombia

Abstract A cross-sectional study was conducted in Colombia to recover Brucella spp. DNA from bovine whole-blood samples through probe-based real-time PCR (Probe-qPCR) and by an SNP-based assay, differentiating vaccine strains from field strains. The associated factors for the presence of Brucella-DNA were reported and evaluated using logistical regression models. A total of 656 random cows from 40 herds were selected. Template DNA was obtained based on a modified salting-out protocol. The Probe- qPCR assay using bcsp31 gene amplification showed an efficiency of 92.35%, with a slope of -3.52 reached in the standard curve. The qPCR assay detected 9.5% (n = 62/656; 95% CI: 7.3,12.0) of the animals with Brucella-DNA presence, and 62.5% (n = 25/40; 95% CI: 45.8,77.3) of the herds with Brucella-DNA presence. Using the SNP-based assay, all positive samples were identified as field Brucella strains. In the final regression model at the animal-level, five variables were associated with Brucella-DNA presence: the use of bulls for mating, recorded history of reproductive problems, pregnant cows, parlor milking, and cows belonging to farms ≤ 200 m from the main road. At the herd-level, two variables were associated with Brucella-DNA presence: recorded history of reproductive problems and bulls' use for mating. Given the fluctuant brucellosis prevalence in endemic areas, updated epidemiological studies are necessary to evaluate the disease dynamic, and if established prevention and control measures have been effective or need to be adjusted. The increase in the prevalence of brucellosis in animal reservoirs creates an important risk of transmission in humans.