Andy Wales

Dr Andrew Wales

Research Fellow

Academic and research departments

School of Veterinary Medicine.

My publications


Rebecca J Gosling, Ian Mawhinney, Kurt Richardson, Andrew Wales, Rob Davies (2021)Control of Salmonella and Pathogenic E. coli Contamination of Animal Feed Using Alternatives to Formaldehyde-Based Treatments, In: Microorganisms (Basel)9(2)263 MDPI
This study compared a novel non-formaldehyde combination product developed for pathogen control in animal feed Finio (A), with a panel of three commonly used organic acid feed additive products: Fysal (B), SalCURB K2 (C) and Salgard (D). Products were evaluated for their ability to reduce Salmonella Typhimurium DT104 and avian pathogenic Escherichia coli in poultry feed. A commercial layer-hen mash was treated with each product and then mixed with feed previously contaminated (via inoculated meat and bone meal) with either Salmonella or E. coli. After 24 h at room temperature, 10 replicate samples were taken from each preparation and plate counts were performed using a selective agar. All concentrations of product A (0.5, 1.0, 1.5, 2.0 and 2.5 kg per metric tonne (MT)) plus the higher concentration of products B and D (6.0 kg MT−1) significantly reduced Salmonella counts compared with those in the untreated control group (p < 0.05). Product C did not significantly reduce levels of Salmonella under these conditions. Because of the poor recovery of E. coli, statistical comparisons for this organism were limited in scope, but only product A at the highest concentration appeared to have eliminated it.
Andrew Wales, Robert Davies (2020)Review of hatchery transmission of bacteria with focus on Salmonella, chick pathogens and antimicrobial resistance, In: World's Poultry Science Journal76(3)pp. 517-536 Taylor & Francis
Commercial poultry hatcheries potentially provide a sanitary barrier between breeder flocks and their progeny. This is important, particularly within the pyramid breeding structures in integrated poultry production systems. However, the operation of hatcheries and their focal position connected with multiple flocks, both on the input and output sides, means that they are vulnerable to being reservoirs of infectious agents. Of particular concern for hatcheries is the pseudo-vertical transmission of bacteria that are initially deposited at the surface of forming or freshly laid eggs. These bacteria (of which Salmonella enterica is a prime example) can subsequently be present in the chick, as well as spreading within the hatchery environment to colonise other hatching birds. Furthermore, if such infectious organisms become persistent in parts of the hatchery environment, this allows their repeated transfer to hatching individuals or even (via personnel and fomites) to transfer back into breeding flocks supplying the hatchery. The use of antimicrobial drugs in hatcheries adds the further hazard of seeding progeny with antimicrobial-resistant (AMR) organisms. The mechanisms of hatchery, egg and subsequent chick contamination have been understood, and strategies to counteract the spread and persistence of infectious agents are well-established. However, many studies examining bacterial pathogens and AMR organisms in poultry production implicate hatcheries, either as a link in a chain or as a source of such agents. This review outlines the challenges posed by hatchery operation to control of bacterial transmission, it examines the contemporary and historical evidence for such phenomena, and it briefly discusses strategies to counteract the issue.
Alastair S Macdonald, Mark A Chambers, Roberto La Ragione, Kayleigh Wyles, Matthieu Poyade, Andrew Wales, Naomi Klepacz, Tom R Kupfer, Fraje Watson, Shona Noble (2021)Addressing Infection Risk in Veterinary Practice through the Innovative Application of Interactive 3D Animation Methods, In: The Design Journal24(1)pp. 51-72 Routledge
Antimicrobial resistance is of growing concern in human and animal health. The aim of this study was to raise awareness and perception of risk of infection-related behaviours during routine preparation for veterinary surgery. We took a multi-disciplinary and multi-method approach to 'make visible, the invisible' by illustrating how microbial contamination can be spread during the preparation process for surgical procedures. The design-led visualization approach enhanced inter-disciplinary team and workshop participant contributions during the co-development of an innovative digital tool to support training for veterinary practitioners and students. After experiencing the intervention, 92% of 51 participants agreed to change their behaviour and stated an intention to implement an infection control behaviour that aligned with training objectives. The 3D graphics enhanced the delivery of training content by making difficult and abstract contamination concepts easy to understand. A similar approach could be taken for human health applications.
Andrew Wales, VM Allen, RH Davies (2009)Chemical treatment of animal feed and water for the control of Salmonella, In: FOODBORNE PATHOGENS AND DISEASE7(1)pp. 3-15 MARY ANN LIEBERT INC
The control of Salmonella in animal feedstuffs is important, principally to protect the human food chain from contamination by Salmonella derived from infected animals. The transmission of Salmonella from animal feeds to animals, and onwards to human food products, has been convincingly documented. This is especially important for chicken breeding and laying flocks and pigs, in view of the consequences of recent or imminent control legislation in the European Union. Animal feed ingredients, particularly animal and plant-derived protein meals, are frequently contaminated with Salmonella either from source or from processing plant, and recontamination in compounding mills is an additional problem. Several complementary strategies have been used to control this feed contamination, and these include a range of chemical treatments. The principal agents used are: organic acids and their salts, formaldehyde, and bacterial membrane disruptors such as terpenes and essential oils. Experimental agents include chlorate compounds. Many products use blends of agents from the same or different chemical groups to achieve synergistic or combination effects. The present review draws upon published and company data to describe the various modes of action and efficacies of different chemical agents delivered in feed or in drinking water against Salmonella occurring in feed or in livestock environments. Reasons for the failure of protection are explored, along with problems in usage such as corrosion and reduced palatability. Given the wide array of products available with contrasting modes of action, the need for standardised tests of efficacy is also discussed.
Andrew Wales, RH Davies (2011)A critical review of Salmonella Typhimurium infection in laying hens., In: Avian Pathology40(5)pp. 429-436 Taylor & Francis
Salmonella Typhimurium has been reported to contaminate egg production across the World, but where Salmonella Enteritidis is endemic it is this latter serovar that dominates egg-borne salmonellosis. However, Salmonella Typhimurium is a major foodborne pathogen so it is important to understand how it can impact the microbiological safety of eggs and what serovar-specific control strategies may be appropriate in the future as control over Salmonella Enteritidis continues to improve. To that end, the present review examines the published literature on Salmonella Typhimurium in laying hens and eggs, with particular reference to comparative studies examining different serovars. Experimentally Salmonella Enteritidis is more often isolated from egg contents and seems to adhere better to reproductive tract mucosa, whilst Salmonella Typhimurium appears to provoke a more intense tissue pathology and immune response, and flock infections are more transient. However, it is observed that in many cases the present body of evidence does not identify clear differences between specific behaviours of the serovars Typhimurium and Enteritidis, whether in laying hens, in their eggs, or in the laying environment. It is concluded that further long-term experimental and natural infection studies are needed in order to generate a clearer picture.
Andrew Wales, Joanna Lawes, Robert Davies (2019)How to… Advise clients about raw feeding dogs and cats, In: BSAVA Companion2019(8)pp. 10-15 British Small Animal Veterinary Association (BSAVA)

Feeding pet dogs and cats on raw, unprocessed food has recently become markedly more popular in the UK and elsewhere in the developed world. There is currently a lack of formal survey data to document this phenomenon, but conversations with clients and a proliferation of raw food marketing and sales outlets attest to growing numbers of pets being fed in this fashion. Sales in the commercial part of this sector may have generated around £90 million in 2018 according to an estimate by Natures Menu, one of the players in this field (Pearce 2018).

Raw meat-based diets (RMBD), sometimes known as ‘Biologically Appropriate Raw Food’ or ‘Bones and Raw Food’ (BARF) diets, include uncooked ingredients from either livestock or wild animals, and may be home-prepared or commercial, with the latter being supplied as fresh, frozen or freeze-dried complete diets, or as premixes intended to be complemented by raw meat (Freeman et al. 2013). Whilst pre-prepared raw diets are convenient, in the manner of traditional processed complete diets, many raw-feeding owners appear to opt for home preparation. A recent Italian study reported that over 80% of (self-selected) raw feeding owners formulated their own diets (Morelli et al. 2019) whilst in 2016 a large formal survey in the USA found 3% of dog owners bought raw pet food but 17% bought raw or cooked human food for their dogs (APPA 2018).

Andrew Wales, JJ Carrique-Mas, M Rankin, B Bell, BB Thind, RH Davies (2009)Review of the carriage of zoonotic bacteria by arthropods, with special reference to Salmonella in mites, flies and litter beetles, In: Zoonoses and Public Health57(5)pp. 299-314 Wiley
This systematic review considers the relationship between arthropods commonly found on and around livestock premises, and zoonotic bacteria. The principal focus is upon insects and arachnids on poultry units, where houses, litter and manure provide good conditions for the growth, multiplication and protection of flies, beetles and mites, and where zoonotic pathogens such as Salmonella and Campylobacter are prevalent. Other members of the Enterobacteriaceae and the taxa Clostridium, Helicobacter, Erysipelas and Chlamydiaceae are also discussed. Salmonella is widely distributed in the flies of affected livestock units, and is detectable to a lesser degree in beetles and mites. Persistent carriage appears to be common and there is some field and experimental evidence to support arthropod-mediated transmission between poultry flocks, particularly carry-over from one flock to the next. Campylobacter may readily be isolated from arthropods in contact with affected poultry flocks, although carriage is short-lived. There appears to be a role for flies, at least, in the breaching of biosecurity around Campylobacter-negative flocks. The carriage of other zoonotic bacteria by arthropods has been documented, but the duration and significance of such associations remain uncertain in the context of livestock production.
Andrew Wales, M Breslin, B Carter, R Sayers, R Davies (2007)A longitudinal study of environmental salmonella contamination in caged and free-range layer flocks, In: Avian Pathology36(3)pp. 187-197 Taylor & Francis:
The environmental contamination by salmonella was examined over a 12-month period in 74 commercial layer flocks from eight farms in the UK, which previously had been identified as being contaminated with salmonella. Samples of faeces, dust, litter, egg belt spillage and wildlife vectors were taken, plus swabs of cages, feeders, drinkers, floors, egg belts and boots. Some sampling was performed in each month of the year. Numerous serovars were detected but Salmonella Enteritidis was the only persistent serotype found among single-age flocks. There was a significant correlation between qualitative environmental samples and semiquantitative faeces samples. The level of environmental contamination increased significantly over time. There were significant temperature and seasonal effects upon contamination. Wildlife vectors proved to be sensitive samples for the detection of salmonella. The efficacy of cleaning and disinfection upon residual salmonella contamination, and upon subsequent flock contamination, was highly variable between and within premises. The variability between detected prevalences over time and between flocks indicates a need for regular, sensitive monitoring of flocks for salmonella to permit targeting of control measures aimed at eliminating contamination of the layer environment by salmonella. There is substantial scope for improvement of cleaning and disinfection procedures.
M Kirchner, I McLaren, FA Clifton-Hadley, E Liebana, Andrew Wales, RH Davies (2012)A comparison between longitudinal shedding patterns of Salmonella Typhimurium and Salmonella Dublin on dairy farms, In: Veterinary Record171(8) BMJ Publishing Group
Salmonella in cattle herds may behave as epidemic or endemic infections. An intensive longitudinal sampling study across all management groups and ages on six dairy farms in the UK was used to examine patterns of Salmonella shedding, following the prior identification of either Salmonella Dublin (SD) (three farms) or Salmonella Typhimurium (ST) (three farms) on the premises in the context of clinical salmonellosis. Individual faeces, pooled faeces and environmental samples (total 5711 samples), taken approximately every six weeks for 15–24 weeks, were cultured for Salmonella. SD was detected at low frequency (on any visit, 0.5–18.3 per cent of samples positive) and most consistently in calves. By contrast, ST was isolated at higher frequency (on any visit, 6.8–75 per cent of samples positive), and in higher numbers, up to 107 cfu/g faeces. Significantly more samples from calves were positive for ST than were positive for SD (50.6 per cent v 3.1 per cent; P < 0.001), which was also true for milking cows (46.3 per cent v 4.4 per cent; P < 0.001). The differences could help to explain the different patterns of bovine infection classically associated with these two serovars in the UK. No consistent effect upon shedding was seen among the ST-infected herds following vaccination.
Andrew Wales, IM McLaren, S Bedford, JJ Carrique-Mas, AJC Cook, RH Davies (2009)Longitudinal survey of the occurrence of Salmonella in pigs and the environment of nucleus breeder and multiplier pig herds in England, In: VETERINARY RECORD165(22)pp. 648-657 BRITISH VETERINARY ASSOC
Epidemiological findings are reported from pig breeding units that were visited repeatedly and sampled intensively for environmental Salmonella contamination. Eight pig breeding units previously associated with Salmonella Typhimurium were visited during up to seven years. Samples from voided faeces, surfaces, fomites and wildlife were cultured. Certain serovars were isolated repeatedly on certain units, whilst others were detected only once or intermittently. A few serovars were isolated consistently on some units but only intermittently on others. There was an association between Salmonella in pens and in their immediate environment. S. Typhimurium was significantly associated with growing pigs. Pens holding breeding stock for production herds were frequently Salmonella-positive. Herds under common ownership showed similar serovar combinations. Cleaning and disinfection was frequently ineffective. Wildlife serovars were typical of the associated premises. On one unit, a low level of Salmonella was attributed to a small herd size, good cleaning and disinfection and good rodent control. The study has shown that breeding herds are susceptible to endemic infections with multiple Salmonella serovars and that cleaning, disinfection and vector control may in many cases be inadequate. Finally, the prevalence of S. Typhimurium may be greater in youngstock, which has important implications for public health.
RH Davies, Andrew Wales (2013)Salmonella contamination of cereal ingredients for animal feeds, In: Veterinary Microbiology166(3-4)pp. 543-549 Elsevier
Cereal ingredients for animal feedstuffs may become contaminated by Salmonella on their farms of origin. This is often concentrated in multiple foci, owing to contamination by rodents and other wildlife which may be missed by routine sampling, and may involve serovars of particular public health significance, such as Salmonella Typhimurium (STM). The study examined such contamination in domestically-produced cereal ingredients in the United Kingdom. Cereal-producing farms with associated cattle or pig enterprises (43) and feedmills (6) were investigated, following the isolation of STM from their premises (feedmills) or STM DT104 from their livestock (farms) by routine surveillance. Cereal samples from feedmills yielded two STM isolates from the same premises, of the same phage types as were isolated from wild bird faeces at ingredient intake and product loading areas. Farm investigations identified numerous Salmonella serovars, including STM, on grain harvesting and handling equipment, in grain storage areas, and in wildlife samples. Mice were removed from one pig farm and shed Salmonella Derby and Salmonella Bovismorbificans for 10 months afterwards. Grain stores more than one kilometre away from livestock areas were rarely found to be contaminated with STM. The principal issues with Salmonella contamination of cereals appeared to be the use of livestock areas as temporary grain stores on cattle farms, and access to stored grain by wildlife and domestic animals.
Alistair Macdonald, Mark Chambers, Roberto La Ragione, Kayleigh Wyles, Matthieu Poyade, Andrew Wales, Naomi Klepacz, Tom Kupfer, Fraje Watson, Shona Noble (2020)Using novel visualisation methods to combat infection risk during clinical practices., In: Proceedings of the 6th International Conference on Design4Health
Andrew Wales, J Weaver, IM McLaren, RP Smith, D Mueller-Doblies, RH Davies (2013)Investigation of the Distribution of Salmonella within an Integrated Pig Breeding and Production Organisation in the United Kingdom, In: ISRN Veterinary Science2013943126 Hindawi Publishing Corporation
To examine patterns of Salmonella herd infections in units linked by common sources of pigs, the study examined pooled pen faeces samples from 161 nursery and finishing units in a UK integrated pig enterprise. An epidemiological questionnaire was also completed by investigators for each farm. Salmonella was isolated from 630 (19.5%) of the samples: S. Typhimurium was found in 387 (12%) and S. Derby in 157 (4.9%) samples; 111 units yielded at least one sample containing Salmonella. The proportion of Salmonella-positive samples from positive farms ranged from 5% to 95%. In a univariable risk factor analysis, increasing length of time as a pig farm was positively associated with the detection of Salmonella in a herd. Larger farms (>500 pigs) were significantly more likely to be positive for S. Typhimurium than smaller farms. There was an association between Salmonella serovars isolated in the present study and those subsequently isolated in breeding herds linked to the integration.
Salmonella infection of laying flocks in the UK is predominantly a problem of the persistent contamination of layer houses and associated wildlife vectors by S. Enteritidis. Methods for its control and elimination include effective cleaning and disinfection of layer houses between flocks, and it is important to be able to measure the success of such decontamination. A method for the environmental detection and semi-quantitative enumeration of salmonellae was used and compared with a standard qualitative method, in twelve Salmonella-contaminated caged layer houses before and after cleaning and disinfection. The quantitative technique proved to have comparable sensitivity to the standard method, and additionally provided insights into the numerical Salmonella challenge that replacement flocks would encounter. Elimination of S. Enteritidis was not achieved in any of the premises examined although substantial reductions in the prevalence and numbers of salmonellae were demonstrated, while in others an increase in contamination was observed after cleaning and disinfection. Particular problems with feeders and wildlife vectors were highlighted. The use of a quantitative method assisted the identification of problem areas, such as those with a high initial bacterial load or those experiencing only a modest reduction in bacterial count following decontamination.
Roberto La Ragione, MJ Woodward, M Kumar, J Rodenberg, H Fan, Andrew Wales, K Karaca (2013)Efficacy of a Live Attenuated Escherichia coli O78∶K80 Vaccine in Chickens and Turkeys, In: Avian Diseases57(2)pp. 273-279 American Association of Avian Pathologists
A candidate live vaccine for avian pathogenic Escherichia coli (APEC) was constructed from a virulent field APEC O78 strain by mutation of the aroA gene. The mutant was highly similar to the parent wild-type strain in respect of colony morphology, motility, growth in suspension, hemagglutination, Congo Red binding, HEp-2 cell adhesion, and the elaboration of surface antigens type 1 fimbriae and flagella, although production of curli fimbriae was reduced marginally. The mutant proved avirulent when inoculated into 1-day-old chicks by spray application and when presented again in the drinking water at 7 days of age. Chickens and turkeys vaccinated with an O78 aroA mutant were protected against a challenge at 6 wk of age by virulent APEC strains.
Andrew Wales, M Breslin, R Davies (2006)Semi-quantitative assessment of the distribution of Salmonella in the environment of caged layer flocks, In: Journal of Applied Microbiology101(2)pp. 309-318 Wiley

To evaluate a semi-quantitative technique for the enumeration of Salmonella in the environment of layer flocks, and to compare findings with those of a standard qualitative technique

Methods and Results:

Samples were taken from faeces, floor dust, dust on cages, feeders and egg belts. After mixing with buffered peptone water, serial dilutions were prepared and culture was performed using pre-enrichment, then plating on semi-solid selective and solid isolation media. Comparison with a qualitative pre-enrichment technique indicated a similar sensitivity for both methods despite smaller sample sizes. The numbers of Salmonella detected for a site or sample type did not correlate closely with the prevalence of positive samples.


The sensitive detection and quantification of Salmonella in the flock environment is practicable with the technique described. Quantitative data in many cases does not correlate with qualitative findings. Significance and Impact of Study: The significance of certain environmental factors and interventions in the maintenance and dissemination of Salmonella in poultry houses may be over- or under- represented by prevalence data alone. The technique described allows the issue of poultry house contamination to be examined from a new perspective.

Andrew Wales, RH Davies (2013)Environmental Aspects of Salmonella, In: Salmonella in Domestic Animalspp. 399-425 CAB International
Salmonella remains a major cause of economic loss in domestic livestock and human food poisoning worldwide. In the last 10 years there have been major advances in understanding the salmonella organism, meaning a compiled source of the new research is urgently needed. With fully updated chapters and new coverage of genome structure, virulence, vaccine development, molecular methods for epidemiology and exotics, this second edition is an invaluable resource for researchers of animal and human health.
EJ Threlfall, J Wain, T Peters, C Lane, E de Pinna, CL Little, Andrew Wales, RH Davies (2014)Egg-borne infections of humans with Salmonella: not only an Enteritidis problem, In: World's Poultry Science Journal70(1)pp. 15-26 Cambridge University Press
The principal salmonella serovar associated with infections linked to eggs and egg products in the UK, most European countries and North America is Salmonella enteritidis. However, other serovars have also been implicated in a number of egg-associated outbreaks, most notably S. typhimurium exhibiting a range of phage types. The present article reviews human egg-associated salmonellosis associated with non-S. enteritidis serovars, predominantly in the European Union (EU) but also world-wide, using information from published literature and epidemiological databases. There are also brief reviews of S. enteritidis and of mechanisms leading to egg contamination by salmonella. The numbers of egg-associated infections caused by non-S. enteritidis serovars are fairly substantial (for example 22% of outbreaks and 11.5% of more than 20,000 cases in the EU in 2008), and such infections have resulted in hospitalisations and deaths. Furthermore, in parts of the world where S. enteritidis historically has not penetrated laying hen breeding flocks, egg-related salmonellosis is a problem associated specifically with non-S. enteritidis serovars. Control measures to limit the incidence of S. enteritidis and S. typhimurium in poultry flocks are vital. It is therefore important that close surveillance of salmonellosis incidence and serovars in laying flocks is used to establish suitable biosecurity and vaccination programmes throughout EU Member States and elsewhere.
Andrew Wales, Robert Davies (2019)Antimicrobial drug resistance in Salmonella and related organisms in poultry - what do we know about risk factors?, In: Proceedings of the 13th Turkey Science and Production Conference Turkeytimes
NM Taylor, RH Davies, A Ridley, C Clouting, Andrew Wales, FA Clifton- Hadley (2008)A survey of fluoroquinolone resistance in E. coli and thermophilic Campylobacter spp. on poultry and pig farms in Great Britain, In: Journal of Applied Microbiology105(5)pp. 1421-1431 Wiley

To estimate the proportions of farms on which broilers, turkeys and pigs were shedding fluoroquinolone (FQ)-resistant E. coli or Campylobacter spp. near to slaughter.

Methods and Results:

Freshly-voided faeces were collected on 89 poultry and 108 pig farms and cultured with media containing 1.0 mg l-1 ciprofloxacin. Studies demonstrated the specificity of this sensitive method, and both poultry and pig sampling yielded FQ-resistant E. coli on 60% of farms. FQ-resistant Campylobacter spp. were found on around 22% of poultry and 75% of pig farms. The majority of resistant isolates of Campylobacter (89%) and E. coli (96%) tested had minimum inhibitory concentrations for ciprofloxacin of ≥8 mg l-1. The proportion of resistant E. coli and Campylobacter organisms within samples varied widely.


FQ resistance is commonly present among two enteric bacterial genera prevalent on pig and poultry farms, although the low proportion of resistant organisms in many cases requires a sensitive detection technique.

Significance and Impact of Study:

FQ-resistant bacteria with zoonotic potential appear to be present on a high proportion of UK pig and poultry farms. The risk this poses to consumers relative to other causes of FQ-resistant human infections remains to be clarified.

Roberto La Ragione, A Best, MJ Woodward, Andrew Wales (2009)Escherichia coli O157:H7 colonisation in small domestic ruminants, In: FEMS Microbiology Reviews33(2)pp. 394-410 Oxford University Press
Enterohaemorrhagic Escherichia coli (EHEC) O157:H7 was first implicated in human disease in the early 1980s, with ruminants cited as the primary reservoirs. Preliminary studies indicated cattle to be the sole source of E. coli O157:H7 outbreaks in humans, however further epidemiological studies soon demonstrated that E. coli O157:H7 was widespread in other food sources and that a number of transmission routes existed. More recently, small domestic ruminants (sheep and goats) have emerged as important sources of E. coli O157:H7 human infection, particularly with the widespread popularity of petting farms and the increased use of sheep and goat food products, including unpasteurised cheeses. Although the colonisation and persistence characteristics of E. coli O157:H7 in the bovine host have been studied intensively, this is not the case for small ruminants. Despite many similarities with the bovine host, the pathobiology of E. coli O157:H7 in small domestic ruminants does appear to differ significantly from that described in cattle. This review aims to critically review the current knowledge regarding colonisation and persistence of E. coli O157:H7 in small domestic ruminants, including comparisons with the bovine host where appropriate.
NM Taylor, FA Clifton-Hadley, Andrew Wales, A Ridley, RH Davies (2009)Farm level risk factors for fluoroquinolone resistance in E. coli and thermophilic Campylobacter spp. on finisher pig farms, In: Epidemiology & Infection137(8)pp. 1121-1134 Cambridge University Press
Logistic regression, supported by other statistical analyses was used to explore the possible association of risk factors with the fluoroquinolone (FQ)-resistance status of 108 pig finisher farms in Great Britain. The farms were classified as ‘affected’ or ‘not affected’ by FQ-resistant E. coli or Campylobacter spp. on the basis of isolation of organisms from faecal samples on media containing 1 mg.l-1 FQ. The use of FQ was the most important factor associated with finding resistant E. coli and/or Campylobacter, which were found on 79% (FQ-resistant E. coli) and 86% (FQ-resistant Campylobacter) of farms with a history of FQ use. However, resistant bacteria were also found on 19% (FQ-resistant E. coli) and 54% (FQ-resistant Campylobacter) of farms with no history of FQ use. For FQ-resistant E. coli, biosecurity measures may be protective and there was strong seasonal variation, with more farms found affected when sampled in the summer. For FQ-resistant Campylobacter, the buying in of grower stock may increase risk and good on-farm hygiene may be protective. The findings suggest that resistant organisms, particularly Campylobacter, may spread between pig farms.
Andrew D. Wales, Ana B. Vidal, Robert H. Davies, John D. Rodgers (2018)Field Interventions against Colonization of Broilers by Campylobacter, In: Comprehensive Reviews in Food Science and Food Safety18(1)pp. 167-188 Wiley
Poultry accounts for a high proportion of human campylobacteriosis cases, and the problem of Campylobacter colonization of broiler flocks has proven to be intractable. Owing to their broad host range and genetic instability, Campylobacter organisms are ubiquitous and adaptable in the broiler farm environment, colonizing birds heavily and spreading rapidly after introduction into a flock. This review examines strategies to prevent or suppress such colonization, with a heavy emphasis on field investigations. Attempts to exclude Campylobacter via enhanced biosecurity and hygiene measures have met with mixed success. Reasons for this are becoming better understood as investigations focus on houses, ventilation, biosecurity practices, external operators, and compliance, amongst other factors. It is evident that piecemeal approaches are likely to fail. Complementary measures include feed and drinking water treatments applied in either preventive or suppressive modes using agents including organic acids and their derivatives, also litter treatments, probiotics, prebiotics, and alterations to diet. Some treatments aim to reduce the number of Campylobacter organisms entering abattoirs by suppressing intestinal colonization just before slaughter; these include acid water treatment or administration of bacteriophages or bacteriocins. Experimental vaccines historically have had little success, but some recent subunit vaccines show promise. Overall, there is wide variation in the control achieved, and consistency and harmonization of trials is needed to enable robust evaluation. There is also some potential to breed for resistance to Campylobacter. Good and consistent control of flock colonization by Campylobacter may require an as-yet undetermined combination of excellent biosecurity plus complementary measures.
Rebecca J. Gosling, Doris Mueller-Doblies, Francesca Martelli, Javier Nunez-Garcia, Nick Kell, Andre Rabie, Andy D. Wales, Robert H. Davies (2018)Observations on the distribution and persistence of monophasic Salmonella Typhimurium on infected pig and cattle farms, In: Veterinary Microbiology227pp. pp 90-96 Elsevier

Following a rapid rise in cases of monophasic Salmonella Typhimurium DT193 (mST) in humans and pigs since 2007 a detailed study of the prevalence and persistence of mST on pig and cattle farms in Great Britain (GB) was undertaken. Thirteen commercial pig farms and twelve cattle farms, identified as mST-positive from surveillance data, were intensively sampled over a three year period. Five indoor and eight outdoor pig farms and four beef and eight dairy farms were included. Individual and pooled faecal samples were collected from each epidemiological group and environmental samples throughout each farm and the antimicrobial resistance profile determined for a selection of mST-positive isolates.

Indoor pig farms had a higher mST prevalence than outdoor pig farms, and across both cattle and pig farms the juvenile animals had a higher mST prevalence than the adult animals. Overall, mST prevalence decreased with time across all pig farms, from 25% to less than 15% of environmental samples and 22% to 15% of pooled faecal samples; only one organic outdoor breeding farm was Salmonella-negative at the end of the study. Across the cattle farms no mST was detected by the end of the study, apart from one persistent farm. Clearance time of mST was between seven and twenty-five months. Farms were selected based on having the antimicrobial resistance profile ampicillin, streptomycin, sulphonamides and tetracycline (A, S, SU, T), although resistance to trimethoprim-potentiated sulphamethoxazole was also identified on five pig farms sampled.

This study provided a detailed insight into the distribution and persistence of mST on individual pig and cattle farms in GB. It has identified variation in mST shedding of individual animals, and the data can be applied to the wider livestock industry when considering the distribution of mST once identified on an individual farm.

Andrew Wales, AJC Cook, RH Davies (2011)Producing Salmonella-free pigs: a review focusing on interventions at weaning, In: VETERINARY RECORD168(10)pp. 267-276 BMJ PUBLISHING GROUP
Salmonella infection in pig production is typically endemic and largely asymptomatic, and is a cause of substantial concern among food safety bodies, prompting voluntary and legislative responses aimed at monitoring and reducing the number of Salmonella-infected animals entering the human food chain. Elimination of the problem at an early stage of production is highly desirable, and to this end the present review examines published evidence on the carriage of Salmonella by piglets before and after weaning, plus evidence on the dynamics of Salmonella infection in the weaner and grower stages of pig production, the effects of maternal immunity, and risk factors for Salmonella excretion after weaning. Various interventions to reduce or eliminate Salmonella infection in young pigs have been tried, such as vaccination, competitive exclusion, feed and water treatments, antibiotic administration, disinfection of animals, and segregated weaning to clean accommodation. The evidence on the effectiveness of these is considered, and the last is examined in some detail as it appears presently to offer the best chance of eliminating Salmonella from growing stock.
AD Wales, FA Clifton-Hadley, AL Cookson, MP Dibb-Fuller, RM La Ragione, KA Sprigings, GR Pearson, MJ Woodward (2001)Experimental infection of six-month-old sheep with Escherichia coli O157 : H7, In: VETERINARY RECORD148(20)pp. 630-631 BRITISH VETERINARY ASSOC
AL Cookson, AD Wales, JM Roe, CM Hayes, GR Pearson, MJ Woodward (2002)Variation in the persistence of Escherichia coli O157 : H7 in experimentally inoculated 6-week-old conventional lambs, In: JOURNAL OF MEDICAL MICROBIOLOGY51(12)pp. 1032-1040 LIPPINCOTT WILLIAMS & WILKINS
RH Davies, Andrew Wales (2010)Investigations of Salmonella contamination in poultry feedmills in the UK, In: Journal of Applied Microbiology109(4)pp. 1430-1440 Wiley

To investigate and compare commercial and farm-level milling operations in respect of the monitoring and control of Salmonella contamination.

Methods and Results:

Four commercial feedmills and four on-farm poultry feed mixers were intensively sampled. Samples included dust and spillages and were cultured for Salmonella. Serovars in ingredients on farms were associated with wildlife and/or livestock, whereas those in commercial mill ingredients were associated with domestically-produced cereals and imported vegetable protein. Endemic contamination of two commercial feedmills was reflected in isolates obtained from finished products and destination flocks. Renovation of equipment and chemical treatment of equipment and feed had not removed endemic strains, and previous routine monitoring in the commercial mills had not revealed the degree of contamination found in the present investigations.


Ingredient contamination was diverse and reflected the sources and storage environments used by mills and farms, respectively. The use of dust and spillage samples showed a clear sensitivity advantage over the previously-used monitoring methods in the feedmills.

Significance and Impact of Study:

Monitoring for Salmonella contamination of commercial feedmills requires sensitive methods, such as those employed in the present study. This is particularly important for endemic contamination.

MJ Woodward, A Best, KA Sprigings, GR Pearson, AM Skuse, A Wales, CM Hayes, JM Roe, JC Low, RM La Ragione (2003)Non-toxigenic Escherichia coli O157 : H7 strain NCTC12900 causes attaching-effacing lesions and eae-dependent persistence in weaned sheep, In: INTERNATIONAL JOURNAL OF MEDICAL MICROBIOLOGY293(4)pp. 299-308 URBAN & FISCHER VERLAG
Robert Davies, Andrew Wales (2019)Antimicrobial Resistance on Farms: A Review Including Biosecurity and the Potential Role of Disinfectants in Resistance Selection, In: Comprehensive Reviews in Food Science and Food Safety18(3)pp. 753-774 Wiley
Resistance to therapeutic antimicrobial agents is recognized as a growing problem for both human and veterinary medicine, and the need to address the issue in both of these linked domains is a current priority in public policy. Efforts to limit antimicrobial resistance on farms has so far focused on control of the supply and use of antimicrobial drugs, plus husbandry measures to reduce infectious disease. In the United Kingdom (UK) and some other countries, substantial progress has been made recently against targets on agricultural antimicrobial drug use. However, evidence suggests that resistant pathogenic and commensal bacteria can persist and spread within and between premises despite declining or zero antimicrobial drug use. Reasons for this are likely complex and varied but may include: bacterial adaptations to ameliorate fitness costs associated with maintenance and replication of resistance genes and associated proteins, horizontal transmission of genetic resistance determinants between bacteria, physical transfer of bacteria via movement (of animals, workers, and equipment), ineffective cleaning and disinfection, and coselection of resistance to certain drugs by use of other antimicrobials, heavy metals, or biocides. Areas of particular concern for public health include extended-spectrum cephalosporinases and fluoroquinolone resistance among Enterobacteriaceae, livestock-associated methicillin-resistant Staphylococcus aureus, and the emergence of transmissible colistin resistance. Aspects of biosecurity have repeatedly been identified as risk factors for the presence of antimicrobial resistance on farm premises, but there are large gaps in our understanding of the most important risk factors and the most effective interventions. The present review aims to summarize the present state of knowledge in this area, from a European perspective.
R. H. Davies, J. R. Lawes, A. D. Wales (2019)Raw diets for dogs and cats: a review, with particular reference to microbiological hazards, In: Journal of Small Animal Practice60(6)pp. 329-339 Wiley
There is a recent trend to feed pet dogs and cats in Britain and other developed countries on raw meat and animal by‐products using either commercial preparations or home recipes. This shift from heat‐treated processed food has been driven by perceived health benefits to pets and a suspicion of industrially produced pet food. The diets of wild‐living related species have been used as a rationale for raw feeding, but differences in biology and lifestyle impose limitations on such comparisons. Formal evidence does exist for claims by raw‐feeding proponents of an altered intestinal microbiome and (subjectively) improved stool quality. However, there is currently neither robust evidence nor identified plausible mechanisms for many of the wide range of other claimed benefits. There are documented risks associated with raw feeding, principally malnutrition (inexpert formulation and testing of diets) and infection affecting pets and/or household members. Surveys in Europe and North America have consistently found Salmonella species in a proportion of samples, typically of fresh‐frozen commercial diets. Another emerging issue concerns the risk of introducing antimicrobial‐resistant bacteria. Raw pet food commonly exceeds hygiene thresholds for counts of Enterobacteriaceae. These bacteria often encode resistance to critically important antibiotics such as extended‐spectrum cephalosporins, and raw‐fed pets create an elevated risk of shedding such resistant bacteria. Other infectious organisms that may be of concern include Listeria, shiga toxigenic E scherichia coli , parasites such as Toxoplasma gondii and exotic agents such as the zoonotic livestock pathogen Brucella suis, recently identified in European Union and UK raw pet meat imported from Argentina.
RH Davies, Andrew Wales (2014)Developments in Salmonella control in eggs, In: Advances in microbial food safety2 Woodhead Publishing
Research and legislation in food microbiology continue to evolve, and outbreaks of foodborne disease place further pressure on the industry to provide microbiologically safe products. This second volume in the series Advances in Microbial Food Safety summarises major recent advances in this field, and complements volume 1 to provide an essential overview of developments in food microbiology. Part one opens the book with an interview with a food safety expert. Part two provides updates on single pathogens, and part three looks at pathogen detection, identification and surveillance. Part four covers pathogen control and food preservation. Finally, part five focuses on pathogen control management. Extends the breadth and coverage of the first volume in the series Includes updates on specific pathogens and safety for specific foods Reviews both detection and management of foodborne pathogens
Andrew Wales, RH Davies (2016)Salmonella vaccination in pigs: a review, In: Zoonoses and Public Health64(1)pp. 1-13 Wiley
The control of Salmonella enterica in pig production is necessary for both public and animal health. The persistent and frequently asymptomatic nature of porcine Salmonella infection and the organism's abilities to colonize other animal species and to survive in the environment mean that effective control generally requires multiple measures. Vaccination is one such measure, and the present review considers its role and its future, drawing on studies in pigs from the 1950s to the present day. Once established in the body as an intracellular infectious agent, Salmonella can evade humoral immunity, which goes some way to explaining the often disappointing performance of inactivated Salmonella vaccines. More recent approaches, using mucosal presentation of antigens, live vaccines and adjuvants to enhance cell-mediated immunity, have met with more success. Vaccination strategies that involve stimulating both passive immunity from the dam plus active immunity in offspring appear to be most efficacious, although either approach alone can yield significant control of Salmonella. Problems that remain include relatively poor control of Salmonella serovars that are dissimilar to the vaccine antigen mix, and difficulties in measuring and predicting the performance of candidate vaccines in ways that are highly relevant to their likely use in commercial production.
Concerns have been raised in recent years regarding co-selection for antibiotic resistance among bacteria exposed to biocides used as disinfectants, antiseptics and preservatives, and to heavy metals (particularly copper and zinc) used as growth promoters and therapeutic agents for some livestock species. There is indeed experimental and observational evidence that exposure to these non-antibiotic antimicrobial agents can induce or select for bacterial adaptations that result in decreased susceptibility to one or more antibiotics. This may occur via cellular mechanisms that are protective across multiple classes of antimicrobial agents or by selection of genetic determinants for resistance to non-antibiotic agents that are linked to genes for antibiotic resistance. There may also be relevant effects of these antimicrobial agents on bacterial community structure and via non-specific mechanisms such as mobilization of genetic elements or mutagenesis. Notably, some co-selective adaptations have adverse effects on fitness in the absence of a continued selective pressure. The present review examines the evidence for the significance of these phenomena, particularly in respect of bacterial zoonotic agents that commonly occur in livestock and that may be transmitted, directly or via the food chain, to human populations.
VK Morris, JJ Carrique-Mas, D Mueller-Doblies, RH Davies, Andrew Wales, VM Allen (2015)A longitudinal observational study of Salmonella shedding patterns by commercial turkeys during rearing and fattening, showing limitations of some control measures, In: British Poultry Science56(1)pp. 48-57 Taylor & Francis
The onset and progression of Salmonella infections was investigated in commercial turkey flocks from placement at 1 d old until slaughter in “brood and move” systems using a longitudinal observational approach based on faeces and environmental sampling with subsequent culture of Salmonella. Persistent Salmonella Newport contamination was found within rearing houses and on their external concrete aprons after cleaning and disinfection between crops of heavily shedding young birds. Salmonella shedding was often detected by 5 d of age and the frequency of positive samples peaked at 14–35 d. Thereafter Salmonella isolations declined, especially in the later (fattening) stages. Samples were still Salmonella-positive at low prevalence in half of the intensively sampled houses at slaughter age. A number of management interventions to combat Salmonella infection of flocks, including sourcing policy, competitive exclusion cultures and cleaning and disinfection, were inadequate to prevent flock infection, although improved disinfection on one unit was associated with a delay in the onset of flock infection.
NM Taylor, Andrew Wales, AM Ridley, RH Davies (2016)Farm level risk factors for fluoroquinolone resistance in E. coli and thermophilic Campylobacter spp. on poultry farms, In: Avian Pathology45(5)pp. 559-568 Taylor & Francis
Data on husbandry practices, performance, disease and drug use were collected during a cross-sectional survey of 89 poultry meat farms in England and Wales to provide information on possible risk factors for the occurrence of fluoroquinolone (FQ) resistant bacteria. Faeces samples were used to classify farms as ‘affected’ or ‘not affected’ by FQ-resistant E. coli or Campylobacter spp. Risk factor analysis identified the use of FQ on the farms as having by far the strongest association, among the factors considered, with the occurrence of FQ-resistant bacteria. Resistant E. coli and/or Campylobacter spp. were found on 86% of the farms with a history of FQ use. However, a substantial proportion of farms with no history of FQ use also yielded FQ-resistant organisms, suggesting that resistant bacteria may transfer between farms. Further analysis suggested that for Campylobacter spp., onfarm hygiene, cleaning and disinfection between batches of birds and wildlife control were of most significance. By contrast, for E. coli biosecurity from external contamination was of particular importance, although the modelling indicated that other factors were likely to be involved. Detailed studies on a small number of sites showed that FQ-resistant E. coli can survive routine cleaning and disinfection. It appears difficult to avoid the occurrence of resistant bacteria when FQ are used on a farm, but the present findings provide evidence to support recommendations to reduce the substantial risk of the incidental acquisition of such resistance by farms where FQ are not used.
R Davies, RJ Gosling, Andrew Wales, RP Smith (2016)Use of an attenuated live Salmonella Typhimurium vaccine on three breeding pig units: A longitudinal observational field study, In: Comparative Immunology, Microbiology and Infectious Diseases46pp. 7-15 Elsevier
The study examined the effects of a licensed live Salmonella Typhimurium vaccine, administered to sows and gilts on three commercial pig units experiencing clinical salmonellosis associated with S. Typhimurium or its monophasic variant. After vaccination, clinical salmonellosis resolved and shedding of S. Typhimurium declined markedly and persistently on all breeding or breedingfinishing units, during the one- to two-year monitoring period. On two finishing units supplied in part by one of the vaccinated herds, pigs from the vaccinated herd were less likely to shed Salmonella than those from non-vaccinating herds, and Salmonella counts in faeces were also lower from the vaccine-linked animals. Non-Typhimurium Salmonella serovars were isolated typically in fewer than 10% of samples, and showed no clear temporal changes in frequency. Vaccination of dams alone with S. Typhimurium was associated with reduced shedding of closely-related serovars among all age groups in this commercial setting.
F Martelli, R Gosling, I McLaren, Andrew Wales, R Davies (2014)Development and testing of external quality assessment samples for Salmonella detection in poultry samples, In: Letters in Applied Microbiology59(4)pp. 443-448 Wiley
Salmonella-contaminated poultry house dust plus 10 g chicken faeces inoculated with Salmonella Enteritidis and then frozen for storage and transport were used as candidate external quality assurance test samples. Variations in faeces sample preparation, storage and culture were examined initially. This indicated that, within modest limits, the age of the inoculating culture and of the faeces did not affect detection, nor did swirling the pre-enrichment culture or extending its duration. Under optimal conditions of preparation and storage, Salmonella numbers of 70 colony-forming units (CFU) and above were reliably detected at the originating laboratory. A ring trial was performed, involving 13 external UK laboratories plus the originating laboratory. Faeces samples inoculated with Salmonella Enteritidis were frozen, transported on dry ice and tested by the ISO 6579:2002 (Annex D) method. Detection by the originating laboratory was consistent with the previously established lower limit for reliability of 70 CFU. However, the sensitivity of detection by the external laboratories was apparently poorer in several cases, with significant interlaboratory variation seen at the lowest inoculum level, using Fisher's exact test. Detection of Salmonella in poultry house dust appeared to be more sensitive and uniform among laboratories. Significance and Impact of the Study Salmonella surveillance and control regimes in the European poultry industry and elsewhere require sensitive culture detection of Salmonella in environmental samples, including poultry faeces. A ring trial was conducted, and the results highlighted that some of the participating laboratories failed to identify Salmonella. This suggests that contaminated frozen faeces cubes could be beneficial to assess proficiency, according to the results of this preliminary study. The data obtained in this study can be used as an indication for the design of realistic external quality assurance for laboratories involved in official testing of Salmonella in poultry flocks.
Andrew Wales, I McLaren, A Rabie, RJ Gosling, F Martelli, R Sayers, R Davies (2013)Assessment of the anti-Salmonella activity of commercial formulations of organic acid products, In: Avian Pathology42(3)pp. 268-275 Taylor & Francis
Organic acid products are widely used in the UK poultry industry as feed or water additives. Claims for Salmonella control are made for some of these products, but there are few studies comparing the anti-Salmonella effect of the various products in tests that reflect field application. The present studies examined the effects of 13 commercial blends (four water products and nine feed products) on Salmonella Enteritidis and Typhimurium strains. Initial screening, in nutrient broth, of all products with all strains revealed little variation between strains in respect of maximum inhibitory and bactericidal dilutions of each product. However, between the products there was wide and significant variation in the maximum inhibitory and bactericidal dilutions, spanning a 700-fold range in the case of bactericidal dilutions for feed-associated products. Further tests were performed, examining reductions in inoculated Salmonella numbers in various matrices (water, feed, soiled litter, crop and caecal contents) following the addition of the products at recommended inclusion rates. One product, incorporating formaldehyde in addition to organic acid, was consistently most active in all matrices, exceeding reductions associated with other products by 1 to 3 log units at most time points. Many products showed only modest anti-Salmonella activity, amounting to 0 or 1 log unit above negative controls at many time points, and the most active products were not the same in all matrices. Tap water appeared to enhance the ability of products to reduce Salmonella, in comparison with bottled mineral or river water.
S Belluco, V Cibin, R Davies, A Ricci, Andrew Wales (2015)A review of the scientific literature on the control of Salmonella spp. in food-producing animals other than poultry OIE (World Organisation for Animal Health)
This book presents an extensive summary of the prevalence, epidemiology and control Salmonella in non-avian livestock, as well as a review of attribution studies relating it to human disease. It has 81 pages with seven chapters wherein chapters 1 to 4 highlights Salmonella in pigs, cattle, sheep, and goats, respectively. Chapter 5 dealt on the farm-level control measures, chapter 6 focused on source attribution of Salmonella cases in humans, and the last chapter (7) discussed Salmonella control in farms, and contribution of foodborne salmonellosis from sources other than poultry.