Livestock-associated MRSA survival on house flies (Musca domestica) and stable flies (Stomoxys calcitrans) after removal from a Danish pig farm

Jonno Jorn Stelder,Matt Denwood,Anette Ella Boklund,Lars Bogø Jensen,René Bødker,Lene Jung Kjær,Margrethe Carlsen

doi:10.1038/s41598-021-83228-7

Jonno Jorn Stelder, Matt Denwood + Show 5 more

Open Access

https://doi.org/10.1038/s41598-021-83228-7

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Abstract

We caught stable- and house flies on a Danish LA-MRSA positive pig farm. Stable- and house flies were housed together and culled over time to test for the presence of live LA-MRSA bacteria at 24 h intervals to establish the length of time for which LA-MRSA can persist on flies. On average, 7% of stable flies and 27% of house flies tested positive for LA-MRSA immediately upon removal from the farm. LA-MRSA prevalence decreased over time and estimates based on a Kaplan–Meier time-to-event analysis indicated that the probability of a stable- or house fly testing positive for LA-MRSA was 5.4% and 7.8% after 24 h, 3.5% and 4.3% after 48 h, 3.1% and 2.2% after 72 h and 0.4% and 0% after 96 h of removal from the pig farm, respectively. Simultaneously, we found that caged cultivated house flies became carriers of LA-MRSA, without direct contact with pigs, in the same proportions as wild flies inside the farm. We provide distance distributions of Danish pig farms and residential addresses as well as the calculated maximum dispersal potentials of stable- and house flies, which suggest that there is a potential for stable- and house flies dispersing live LA-MRSA bacteria into the surrounding environment of a pig farm. This potential should therefore be considered when modelling the spread between farms or the risk posed to humans living in close proximity to LA-MRSA pig farm sources.

Highlights

The emerging Methicillin-resistant strain of S. aureus associated with livestock (LA-MRSA), has seen a rapid increase and spread amongst pig farms in recent years[1], in the N etherlands[2] as well as in Denmark[3]
The binary logistic regression model showed that the initial prevalence of flies that tested positive for LA-MRSA varied significantly at 0 h after collection from the farm
We found a significantly higher odds ratio (OR = 5.550, p < 0.001) in the model of a house fly testing positive for LA-MRSA compared to a stable fly

Summary

Introduction

The emerging Methicillin-resistant strain of S. aureus associated with livestock (LA-MRSA), has seen a rapid increase and spread amongst pig farms in recent years[1], in the N etherlands[2] as well as in Denmark[3]. Due to the spread pattern of human infection cases in rural areas with a high density of pig farms, Anker et al.[1] suggest that the cause of these infections cannot entirely be attributed to environmental spread and that other transmission pathways must be contributing to this Due to their hematophagous and saprophytic foraging behaviours, as well as their breeding behaviour, stable flies and house flies, respectively, play a significant role in the spread and transmission of a wide variety of bacterial and viral pathogens. We can use the different dispersal and flight distances from previous studies to make rough estimates of how far stable- and house flies could potentially fly while carrying live LAMRSA bacteria. The relatively small size of Denmark and the high density of pig farms could make this potential transmission pathway more viable in Denmark compared to other countries

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