Transmission of antimicrobial resistance (AMR) during animal transport

Abstract

The transmission of antimicrobial resistance (AMR) between food-producing animals (poultry, cattle and pigs) during short journeys (< 8 h) and long journeys (> 8 h) directed to other farms or to the slaughterhouse lairage (directly or with intermediate stops at assembly centres or control posts, mainly transported by road) was assessed. Among the identified risk factors contributing to the probability of transmission of antimicrobial-resistant bacteria (ARB) and antimicrobial resistance genes (ARGs), the ones considered more important are the resistance status (presence of ARB/ARGs) of the animals pre-transport, increased faecal shedding, hygiene of the areas and vehicles, exposure to other animals carrying and/or shedding ARB/ARGs (especially between animals of different AMR loads and/or ARB/ARG types), exposure to contaminated lairage areas and duration of transport. There are nevertheless no data whereby differences between journeys shorter or longer than 8 h can be assessed. Strategies that would reduce the probability of AMR transmission, for all animal categories include minimising the duration of transport, proper cleaning and disinfection, appropriate transport planning, organising the transport in relation to AMR criteria (transport logistics), improving animal health and welfare and/or biosecurity immediately prior to and during transport, ensuring the thermal comfort of the animals and animal segregation. Most of the aforementioned measures have similar validity if applied at lairage, assembly centres and control posts. Data gaps relating to the risk factors and the effectiveness of mitigation measures have been identified, with consequent research needs in both the short and longer term listed. Quantification of the impact of animal transportation compared to the contribution of other stages of the food-production chain, and the interplay of duration with all risk factors on the transmission of ARB/ARGs during transport and journey breaks, were identified as urgent research needs.

Keywords: antimicrobial resistance genes (ARGs); antimicrobial‐resistant bacteria (ARB); data gaps; food‐producing animals; lairage; mitigation options; research needs; risk factors.

Figure 1

Description of type of journey, maximal journey duration and journey breaks in accordance with EC 1/2005

Figure 2

Type of movements within the poultry industry. Around 95% of the meat production birds (e.g. poultry and turkey) move twice, from hatchery to farm and from farm to slaughterhouse. Solid lines display main routes of transport for production, while dotted lines show less frequent routes

Figure 3

Type of movements within the pig industry. The scheme summarises the different sort of farms by production objectives. Solid lines display main routes of transport for production, while dotted lines show less frequent routes. Dotted boxes indicate the type of animal that is transported. Some individual steps may be skipped. Nursery units may be part to the commercial breeder farm (farrow to grower farms) with no transport after weaning. Likewise, fattening units may be on the same farm as well (farrow to finish farm). In those cases, less transport is involved. Additional transport may be involved in multi‐site operations. Transport to livestock assembly centres (markets, dealers, shows) occurs in most countries, albeit mostly at small scale. Most pigs move twice, from farm to farm and from farm to slaughter house/abattoir

Figure 4

Cattle breeding and distribution. Solid lines display main routes of transport for production, while dotted lines show less frequent routes. Dotted boxes indicate the type of animal that is transported. Most meat production cattle move at least twice, from the farm of birth to the raising/fattening farm and from that farm to slaughterhouse/abattoir. For all cattle additional movements may occur (e.g. to and from assembly centres, including markets or fairs, or between different parts of the same farm)

Figure 5

Gut–brain axis model for the chicken (adapted from Wickramasuriya et al., 2022)

Figure 6

Routes and means of transport of the animal categories (cattle, pigs and poultry) covered in the current assessment. These include short and long journeys (less and more than 8 h) by different transport vehicles (trucks, trains, livestock vessels, ferries, planes). In accordance with its share among all transports, transport by trucks on the road will be the main focus. Included in the assessment are all transports of production animals from farms to other farms and/or slaughterhouses, also including control posts (stops during the journey), collection or sorting centres and/or auction markets (assembly centres)

Figure 7

Sources of ARB and ARGs in the transport vehicles. The main source of ARB/ARGs in the transport vehicles are the transported animals, which may be carriers and shed ARB/ARGs via their excretions and secretions (e.g. faeces, saliva, respiratory droplets, urine, and vomit). ARB/ARGs may persist in the environment between batches of animals. Other potential contamination sources are bedding material, feed, water and handling equipment. Finally, workers, including personnel involved in animal loading/unloading on farms, at control posts and assembly centres, drivers and inspectors may be sources of ARB/ARGs. Transmission may occur directly between animals, or indirectly, through direct contact with contaminated materials of the truck and the transport equipment (including crates, ramps, handling equipment and loading platforms) or may be airborne

Figure 8

Risk factors for transmission of antimicrobial resistance during animal transport. The AMR status before transport will have a substantial effect on the likelihood of transmission of ARB/ARGs during transport. During transport, health status and environmental conditions are factors affecting the microbiota of animals and the likelihood of ARB/ARGs transmission. Feed withdrawal and stressors were also identified, although the direction of influence on ARB/ARGs transmission (decrease or increase) is unclear. Exposure to ARB/ARG in other animals (either shed or present on their skin or mucosal surfaces) is a major source of contamination for other animals during transport. Environmental exposure to ABR/ARGs is related to the cleanliness of loading and unloading areas and of vehicles, workers related to transport and their transmission through air. The environmental conditions of the transport (e.g. temperature, humidity) are also important for the survival/growth and dispersion of bacteria outside the animal. Transmission is influenced by duration since the exposure to risk factors is prolonged, although there is no evidence to estimate differences between journeys shorter or longer than 8 h

Figure 9

Scheme of potential transport logistics based on AMR criteria. Based on AMR information (AMR load, ARB, ARGs or indirect measures) farms or batches (feedlots) can be categorised by their potential risk and specific measures can be implemented in transport, assembly centres, control posts and/or lairage