Pathogens, patterns of pneumonia, and epidemiologic risk factors associated with respiratory disease in recently weaned cattle in Ireland

Abstract

We examined the pathogens, morphologic patterns, and risk factors associated with bovine respiratory disease (BRD) in 136 recently weaned cattle ("weanlings"), 6-12 mo of age, that were submitted for postmortem examination to regional veterinary laboratories in Ireland. A standardized sampling protocol included routine microbiologic investigations as well as polymerase chain reaction and immunohistochemistry. Lungs with histologic lesions were categorized into 1 of 5 morphologic patterns of pneumonia. Fibrinosuppurative bronchopneumonia (49%) and interstitial pneumonia (48%) were the morphologic patterns recorded most frequently. The various morphologic patterns of pulmonary lesions suggest the involvement of variable combinations of initiating and compounding infectious agents that hindered any simple classification of the etiopathogenesis of the pneumonias. Dual infections were detected in 58% of lungs, with Mannheimia haemolytica and Histophilus somni most frequently recorded in concert. M. haemolytica (43%) was the most frequently detected respiratory pathogen; H. somni was also shown to be frequently implicated in pneumonia in this age group of cattle. Bovine parainfluenza virus 3 (BPIV-3) and Bovine respiratory syncytial virus (16% each) were the viral agents detected most frequently. Potential respiratory pathogens (particularly Pasteurella multocida, BPIV-3, and H. somni) were frequently detected (64%) in lungs that had neither gross nor histologic pulmonary lesions, raising questions regarding their role in the pathogenesis of BRD. The breadth of respiratory pathogens detected in bovine lungs by various detection methods highlights the diagnostic value of parallel analyses in respiratory disease postmortem investigation.

The bovine paranasal sinuses: Bacterial flora, epithelial expression of nitric oxide and potential role in the in-herd persistence of respiratory disease pathogens

“…However, recent reports of respiratory disease diagnoses in weanling cattle examined post-mortem in Ireland [22] recorded low frequency of respiratory vaccination in the study population and the authors suspect a similar low frequency of vaccination in the study population of the current study. BPIV-3 was detected by PCR in the sinus of only one animal while BRSV was not detected in the sinus of any animal suggesting that the persistence of BRD-causing viruses is unlikely in the sinuses.…”

Evolving views on bovine respiratory disease: An appraisal of selected key pathogens – Part 1

“…Histophilus somni (formerly Haemophilus somnus) is a nonencapsulated gram negative bacterium associated with a number of clinical syndromes, including respiratory disease, in cattle maintained in feedlot (Gagea et al, 2006) and traditional, smaller, pasturebased husbandry systems (Murray et al, 2016a). H. somni pneumonia is not distinguishable clinically from other causes of BRD (Apley, 2006).…”

“…The prevalence of H. somni detection post-mortem in pneumonic bovine lungs can vary considerably, with up to 40% recorded in some years (Welsh et al, 2004;Murray et al, 2016a). H. somni strains differ in their ability to induce pneumonia in calves (Groom et al, 1988), may be found commensally in the genital (Kwiecien and Little, 1992) and respiratory tract, and can persist in the lung for long periods in the absence of clinical disease (Gogolewski et al, 1989).…”

“…Bovine respiratory disease (BRD) is one of the most commonly diagnosed causes of morbidity and mortality in cattle, both within large feedlots and traditional, smaller, pasture-based husbandry systems (Edwards, 2010;Murray et al, 2016a). The pathogenesis of BRD is often driven by complex interactions of factors associated with the animal, the pathogen and the environment which creates significant challenges in its control (Edwards, 2010).…”

“…Emerging knowledge of a potential role for these 'minor' players (e.g. bovine coronavirus, bovine rhinitis A virus) in the pathogenesis of BRD coupled with the polymicrobial nature of many cases, and the detection of many recognised BRD pathogens in the nasopharynx or lungs of healthy cattle (Caswell, 2014), complicates BRD diagnosis and blurs the precise role played by specific pathogens in eliciting disease (Virtala et al, 1996;Murray et al, 2016a). Determining the likely significance of detection of these pathogens in diseased bovine lungs is important in interpreting pathologic analyses, and in initiating control measures, for the veterinary practitioner and veterinary pathologist alike.…”