A mathematical model of Campylobacter dynamics within a broiler flock

Abstract

Globally, the bacterial genus Campylobacter is one of the leading causes of human gastroenteritis, with its primary route of infection being through poultry meat. Despite decades of study we appear to be no closer to preventing outbreaks within commercial chicken flocks, and the application of biosecurity measures is limited by a lack of understanding of the transmission dynamics within a flock. Our work is the first to undertake a mathematical modelling approach to Campylobacter population dynamics within a flock of broilers (chickens bred specifically for meat). A system of stochastic differential equations is used to investigate the diverse and fluctuating conditions within the gut of a broiler, and models the routes of infection between co-housed birds. The presented model provides mechanistic explanations for key infection dynamics that have been long-observed but very poorly understood. We highlight several driving mechanisms behind observed infection phenomena, simulate experimentally observed inter-strain competition, and present a promising approach to hypothesising new methods of preventing flock outbreaks.The bacteria Campylobacter is one of the most common causes of food poisoning globally. The most common route of infection is through raw chicken meat, as a result of many chicken farms across the world housing fully infected flocks. Despite the magnitude of this public health risk, little is understood of the specifics of how chickens become infected, and the ways that they then infect one another. Our work presents a mathematical model of Campylobacter transmission dynamics within a flock of chickens.We compare the results of the model to real world data sets, explore key dynamical behaviours, and present a sensitivity analysis to highlight the most important factors underpinning outbreaks.

Mechanisms of biodiversity between Campylobacter sequence types in a flock of broiler–breeder chickens

“…Positive samples were then genotyped (MLST), enabling the ST and species of the Campylobacter isolate to be specified. Note that, while multiple STs can occupy a host‐bird simultaneously, it is frequently observed, experimentally (Colles et al, 2019) and theoretically (Rawson et al, 2019), that a single ST will broadly dominate the gut at any given time. Hence, the sole ST recorded from a positive bird is a reflection of which STs are most dominantly expressed at that time point.…”

Can good broiler flock welfare prevent colonization by Campylobacter?

“…Parent age has also been shown to influence egg weight and embryo weight of chicks (Shanawany, 1984). Given the potential importance of maternal antibodies in suppressing Campylobacter in the first few weeks of age (Rawson et al, 2019), parent age could potentially impact the likelihood of Campylobacter colonization. Our results however indicate that factors relating to the parent flock have no effect on any of the metrics considered in this study.…”

“…• Number placed -A numerical variable describing how many broilers made up the flock. While modelling studies have primarily implicated stocking density as a high Campylobacter risk factor, the total flock population may also increase the likelihood of initial flock inoculation (Rawson et al, 2019).…”

“…More directly, lesions on the footpad and arthritis have been shown to be strong predictors of Campylobacter prevalence (Alpigiani et al, 2017), further supporting findings that flock movement patterns and behaviour can also accurately predict Campylobacter prevalence (Colles et al, 2016). Our own previous mathematical modelling studies have highlighted the potential for stocking density (Rawson et al, 2019) to impact the population dynamics of Campylobacter within a flock, and have also shown that the colonization status of an entire flock is greatly impacted by the • Company -A two-factor categorical variable, depicting whether the flock is overseen by company "1" or "2". This variable will also therefore capture differences in company-specific rearing methodologies not represented by our current list of predictor variables.…”

A Mathematical Model of Campylobacter Dynamics Within a Broiler Flock

“…We thank Frances Colles, Adrian Smith, and Martin Maiden for their insight and contribution in discussing the model and our findings. This manuscript has been released as a preprint at https://www.biorxiv.org/content/10.1101/476119v2 (Rawson et al, 2019).…”