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Pathogen-specific prevalence and pathogen associations during outbreaks of Bovine Respiratory Disease in calves in Flanders
Hoflack, G.; Lebrun, M.; Vertenten...
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Objectives: Bovine respiratory disease (BRD) is a major health problem during calf rearing in many farms. The objective of this study was to obtain further insights into the importance of different pathogens involved and possible pathogen associations during outbreaks of BRD in calves in Flanders.
Materials & Methods: A cross-sectional study was performed from January 2019 until December 2021. The target population consisted of cattle herds from the northern part of Belgium (Flanders) with a current acute outbreak of BRD. Respiratory samples, consisting of either nasopharyngeal swabs, broncho-alveolar lavage fluid or lung tissue, were collected from affected calves in those herds and submitted for pathogen detection. Pathogen detection was performed using semi-quantitative real-time PCR test targeting seven bovine respiratory pathogens: bovine respiratory syncytial virus (BRSV), bovine parainfluenzavirus type 3 (PI3V), bovine coronavirus (BCoV), Mannheimia haemolytica, Pasteurella multocida, Mycoplasma bovis, and Histophilus somni. The results were analyzed using R software (R Core Team, 2017). Multivariable logistic regression models were constructed for each of the seven respiratory pathogens. As predictors, the PCR results of the other six pathogens besides the outcome pathogen were considered for the analysis. Additional predictors in the models were season of outbreak occurrence and sample type. Statistical significance was set at p < 0.05.
Results: In total 245 outbreaks of BRD were assessed. At least one pathogen was detected in 185 (75.5%) of those out- breaks. Single as well as multiple viral infections were detected in 31.8 and 43.7% of outbreaks, respectively. BRSV was the most frequently isolated virus (38 positive/245 outbreaks, 15.5%). In 73.7% of outbreaks where BRSV was detected, it was the only viral agent detected. BCoV was detected in 31 out of 245 outbreaks (12.7%) and was the only virus detected in 21 of those outbreaks (67.7%). PI3V was only detected in 3.7% of outbreaks and these were predominantly multiple viral infections (88.9%). Pasteurella multocida, Mannheimia haemolytica, Mycoplasma bovis, and Histophilus somni were detected in, respectively 58.8, 25.3, 21.6, and 20.8 % of the outbreaks.
In the present study, a PCR positive result for BRSV was associated with an increased detection rate of Mycoplasma bovis (OR 2.65, CI95% 1.17-6.01) and PI3V (OR 9.63, CI95% 2.14-52.5). Mannheimia haemolytica was associated with an increased detection rate of PI3V (OR 7.36, CI95% 1.51-53.9), Mycoplasma bovis (OR 2.21, CI95% 1.07-4.55), and Pasteurella multocida (OR 2.19, CI95% 1.09-4.57). Detection of BCoV during an outbreak of BRD was associated with a higher risk for the detection of PI3V (OR 5.96, CI95% 1.24-29.8). Besides the association of Mycoplasma bovis with Mannheimia haemolytica and BRSV, Mycoplasma bovis detection was also associated with a higher risk for the detection of Pasteurella multocida (OR 2.80, CI95% 1.35-6.17), and Histophilus somni (OR 2.96, CI95% 1.46-5.96). A seasonal effect was shown for BRSV (OR 4.85, CI95% 2.09-12.70) and Mannheimia haemolytica (OR 3.09, CI95% 1.54-6.37) isolation, with a higher prevalence in winter and spring compared to summer and autumn. Sample type was only observed to be associated with the isolation rate of Mannheimia haemolytica, with a more frequent isolation from broncho-alveolar lavage fluid than deep naso-pharyngeal swabs (OR 7.9, CI95% 1.29-1.53).
Conclusion: The use of PCR as a diagnostic tool during BRD outbreaks is very valuable since in more than 75% of cases an etiological diagnosis could be established. BRSV and BCoV are the most frequently involved viral pathogens and acted predominantly as single viral agents. We demon-strated a seasonal influence on the occurrence of BRSV and Mannheimia haemolytica with higher risk of disease in winter and spring. Finally, we found multiple interactions between pathogens responsible for BRD outbreaks in calves. This observation could be useful for the implementation of specific combined preventive measures at the farm level.
Keywords: Bovine respiratory disease, calves, diagnosis, PCR.
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Affiliation of the authors at the time of publication
MSD Animal Health, Brussels, Belgium;
MSD Animal Health, Boxmeer, Netherlands
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