A mechanistic model for spread of livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) within a pig herd

Abstract

Before an efficient control strategy for livestock-associated methicillin resistant Staphylococcus aureus (LA-MRSA) in pigs can be decided upon, it is necessary to obtain a better understanding of how LA-MRSA spreads and persists within a pig herd, once it is introduced. We here present a mechanistic stochastic discrete-event simulation model for spread of LA-MRSA within a farrow-to-finish sow herd to aid in this. The model was individual-based and included three different disease compartments: susceptible, intermittent or persistent shedder of MRSA. The model was used for studying transmission dynamics and within-farm prevalence after different introductions of LA-MRSA into a farm. The spread of LA-MRSA throughout the farm mainly followed the movement of pigs. After spread of LA-MRSA had reached equilibrium, the prevalence of LA-MRSA shedders was predicted to be highest in the farrowing unit, independent of how LA-MRSA was introduced. LA-MRSA took longer to spread to the whole herd if introduced in the finisher stable, rather than by gilts in the mating stable. The more LA-MRSA positive animals introduced, the shorter time before the prevalence in the herd stabilised. Introduction of a low number of intermittently shedding pigs was predicted to frequently result in LA-MRSA fading out. The model is a potential decision support tool for assessments of short and long term consequences of proposed intervention strategies or surveillance options for LA-MRSA within pig herds.

Mechanistic modelling of interventions against spread of livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) within a Danish farrow-to-finish pig herd

“…The model consists of two main units, a herd model of a farrow-to-finish pig herd and an epidemic model for LA-MRSA. Both are briefly described below and a more detailed description of the full model can be found in Sørensen et al, 2017 [ 18 ], including a link to the model R-code: https://github.com/anvso/DTU-model .…”

“…Whether a pig became a PS was modelled to depend both on host-related factors and the degree of exposure to LA-MRSA. This was implemented by only assigning a certain fraction of the pigs the potential to become PS, with a probability of becoming PS upon exposure that changed depending on the prevalence within the section where the pig was housed being above or below a given limit [ 18 ]. The duration of shedding for IS varied from 1–26 days.…”

“…One of the main challenges, when modelling spread of LA-MRSA is that the dynamics of infection in pigs are not clear, and assumptions regarding the existence of both intermittent shedders (IS) and persistent shedders (PS) might have a major impact on the results. In this paper, we use a previously published mechanistic individual-based model for spread of LA-MRSA within a pig herd [ 18 ] for simulating the outcome of implementing on-farm interventions within four different areas: 1) Reduced antimicrobial consumption, 2) Reduced number of pigs within each section, 3) Reduced mixing of pigs, and 4) Improved internal biosecurity. Using the Danish situation as an example, where LA-MRSA was isolated from 88% of 57 randomly selected pig herds tested in Denmark [ 19 ], we assume that LA-MRSA has already become fully established within the herd and reached a steady state prevalence in all farm units before the interventions are initiated.…”

Dynamics of Livestock-Associated Methicillin ResistantStaphylococcus aureusin pig farms networks: insight from mathematical modeling and French data

“…Over the last decade, a few mathematical models have been proposed to study the spread of LA-MRSA, within a single pig herd 22,23 , at the scale of a pig farm network [24][25][26] and from a single pig farm to humans 27 . These models allowed to explore the implementation of control interventions based on reduced antimicrobial use, reduced mixing of pigs within and between farms, improved biosecurity, movements restrictions, as well as voluntary eradication of pigs.…”

A role of methicillinresistant Staphylococcus aureus strains and related molecular genetic features in developing purulent-necrotic forms of the diabetic foot syndrome

“…Сложность терапии инфекций, вызванных MRSA, обусловлена их устойчивостью не только к бета-лактамным антибиотикам, но и к широкому кругу препаратов других классов [2]. Традиционно MRSA классифицируют как ассо-циированные с врачебной деятельностью штаммы (HA-MRSA), внебольничные штаммы (CA-MRSA), ассоциированные с животноводством штаммы (LA-MRSA) [27]. В разных странах мира распространены основные генетические клоны данных линий MRSA, различающихся по степени вирулентности и уровню антибиотикорезистентности [10,15,21].…”