Carriage of Bacterial Pathogens in the Bovine Upper Respiratory Tract
: Effects of Respiratory Virus Vaccination

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)

Abstract

Despite the major welfare and economic burdens of bovine respiratory disease worldwide, Pasteurellaceae carriage in cattle has been relatively unexplored. To address this, molecular techniques and epidemiological studies were employed to investigate upper respiratory tract carriage of three important respiratory pathobionts, Histophilus somni, Mannheimia haemolytica and Pasteurella multocida, in cattle in an experimental beef production setting.

Real-time PCR assays were optimised and validated to detect and quantify these three bacterial species. These assays were deployed to investigate pathobiont carriage in a longitudinal study of weaned cattle (n=90) during 2015-2016 winter housing. A separate cohort (n=30) was followed from birth in spring 2016 to just after weaning in November 2016. Carriage was shown to be highly dynamic; different organisms predominated as calves aged, and during housing, carriage patterns were distinct among pathobiont species. Interval-censored exponential survival models estimated the median duration of H. somni and P. multocida carriage at 14.8 (CI95%: 10.6–20.9) and 55.5 (CI95%: 43.3– 71.3) days respectively; higher density P. multocida carriage was associated with slower clearance (p = 0.036).

A double-blind cluster randomised controlled trial was conducted in housed cattle (n=87) over winter 2016-2017 to investigate the effect of bovine respiratory syncytial virus and parainfluenza-3 virus on respiratory bacterial carriage. Viral infection used a bivalent intranasal live-attenuated vaccine following a stepped wedge design. Mixed effect models showed that the M. haemolytica carriage rate declined significantly following respiratory viral infection (odds ratio: 0.48; CI95%: 0.27–0.85). Carriage of H. somni and P. multocida, declined similarly although these trends were not statistically significant. There were no consistent effects of viral infection on pathobiont carriage density.

This research showed that improved molecular techniques can provide valuable novel insights into the carriage and biology of Pasteurellaceae and lays the foundation for further detailed investigations and modelling studies into the epidemiology of bovine respiratory disease.
Date of Award1 Oct 2019
Original languageEnglish
Awarding Institution
  • The University of Bristol
SponsorsBBSRC & Zoetis ltd
SupervisorMark C Eisler (Supervisor), Adam H R Finn (Supervisor), Mick Bailey (Supervisor) & Michael Lee (Supervisor)

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