Jan M. Sargeant

Pre-harvest Interventions to Reduce the Shedding of E. coli O157 in the Faeces of Weaned Domestic Ruminants: A Systematic Review

Our objective was to use formal systematic review methods to evaluate the efficacy of interventions to reduce faecal shedding of Escherichia coli O157 in post‐weaned ruminants by increasing animal resistance. The methodology consisted of an extensive search to identify all potentially relevant research, screening of titles and abstracts for relevance to the research question, quality assessment of relevant research, extraction of data from research of sufficient quality, and qualitative summarization of results. The interventions evaluated included probiotics, vaccination, antimicrobials, sodium chlorate, bacteriophages and other feed additives. There was evidence of efficacy for the probiotic combination Lactobacillus acidophilus NP51 (NPC 747) and Propionibacterium freudenreichii and for sodium chlorate in feed or water. The effectiveness of vaccination varied among studies and among vaccine protocols and there was no consistent evidence to suggest that antibiotic use was associated with a decrease in faecal shedding of E. coli O157, or that current industry uses of antimicrobials were associated with increased faecal shedding. There were an insufficient number of studies available to address the effectiveness of bacteriophages and several other feed additives. In general, few of the primary studies evaluated the interventions under commercial housing conditions with a natural disease challenge, there were inconsistencies in the results among study designs and in some cases among studies within study designs, and a relatively large proportion of publications were excluded based on quality assessment criteria. Few studies reported on associations between the proposed intervention and production parameters, such as average daily gain and feed: gain ratio. While the results suggest that some interventions may be efficacious, there are knowledge gaps in our understanding of the efficacy of pre‐harvest interventions to increase animal resistance to E. coli O157 that require further targeted research.

Diversity, Frequency, and Persistence of Escherichia coli O157 Strains from Range Cattle Environments

ABSTRACT Genetic diversity, isolation frequency, and persistence were determined for Escherichia coli O157 strains from range cattle production environments. Over the 11-month study, analysis of 9,122 cattle fecal samples, 4,083 water source samples, and 521 wildlife fecal samples resulted in 263 isolates from 107 samples presumptively considered E. coli O157 as determined by culture and latex agglutination. Most isolates (90.1%) were confirmed to be E. coli O157 by PCR detection of intimin and Shiga toxin genes. Pulsed-field gel electrophoresis (PFGE) of XbaI-digested preparations revealed 79 unique patterns (XbaI-PFGE subtypes) from 235 typeable isolates confirmed to be E. coli O157. By analyzing up to three isolates per positive sample, we detected an average of 1.80 XbaI-PFGE subtypes per sample. Most XbaI-PFGE subtypes (54 subtypes) were identified only once, yet the seven most frequently isolated subtypes represented over one-half of the E. coli O157 isolates (124 of 235 isolates). Recurring XbaI-PFGE subtypes were recovered from samples on up to 10 sampling occasions and up to 10 months apart. Seven XbaI-PFGE subtypes were isolated from both cattle feces and water sources, and one of these also was isolated from the feces of a wild opossum (Didelphis sp.). The number of XbaI-PFGE subtypes, the variable frequency and persistence of subtypes, and the presence of identical subtypes in cattle feces, free-flowing water sources, and wildlife feces indicate that the complex molecular epidemiology of E. coli O157 previously described for confined cattle operations is also evident in extensively managed range cattle environments.

Global Incidence of Human Shiga Toxin–Producing Escherichia coli Infections and Deaths: A Systematic Review and Knowledge Synthesis

OBJECTIVES Shiga toxin-producing Escherichia coli (STEC) are an important cause of foodborne disease, yet global estimates of disease burden do not exist. Our objective was to estimate the global annual number of illnesses due to pathogenic STEC, and resultant hemolytic uremic syndrome (HUS), end-stage renal disease (ESRD), and death. MATERIALS We searched Medline, Scopus, SIGLE/OpenGrey, and CABI and World Health Organization (WHO) databases for studies of STEC incidence in the general population, published between January 1, 1990 and April 30, 2012, in all languages. We searched health institution websites for notifiable disease data and reports, cross-referenced citations, and consulted international knowledge experts. We employed an a priori hierarchical study selection process and synthesized results using a stochastic simulation model to account for uncertainty inherent in the data. RESULTS We identified 16 articles and databases from 21 countries, from 10 of the 14 WHO Sub-Regions. We estimated that STEC causes 2,801,000 acute illnesses annually (95% Credible Interval [Cr.I.]: 1,710,000; 5,227,000), and leads to 3890 cases of HUS (95% Cr.I.: 2400; 6700), 270 cases of ESRD (95% Cr.I.: 20; 800), and 230 deaths (95% Cr.I.: 130; 420). Sensitivity analyses indicated these estimates are likely conservative. CONCLUSIONS These are the first estimates of the global incidence of STEC-related illnesses, which have not been explicitly included in previous global burden of disease estimations. Compared to other pathogens with a foodborne transmission component, STEC appears to cause more cases than alveolar echinococcosis each year, but less than typhoid fever, foodborne trematodes, and nontyphoidal salmonellosis. APPLICATIONS Given the persistence of STEC globally, efforts aimed at reducing the burden of foodborne disease should consider the relative contribution of STEC in the target population.

ESCHERICHIA COLI O157:H7 IN FREE-RANGING DEER IN NEBRASKA

In order to determine the prevalence and distribution of the human pathogen, Escherichia coli O157:H7, in free-ranging deer, hunters were asked to collect and submit fecal samples from deer harvested during a regular firearm season (14–22 November 1998). Prior to the season, 47% of the hunters with permits in the southeastern Nebraska (USA) study area indicated a willingness to participate in the study. Approximately 25% of successful hunters in the area submitted deer fecal samples. Escherichia coli O157:H7 was cultured from four (0.25%) of 1,608 total samples submitted. All of the fecal samples that were properly identified (1,426) and all that were positive for E. coli O157:H7 were from white-tailed deer (Odocoileus virginianus). We were unable to detect a statistically significant geographic distribution pattern of E. coli O157:H7. The presence of E. coli O157:H7 in the feces of free-ranging deer has implications not only for hunters, consumers of venison, and others in contact with deer or deer feces, but also for the development of strategies aimed at reducing and/or controlling this pathogen in water sources and domestic livestock.

A systematic review of vaccinations to reduce the shedding of Escherichia coli O157 in the faeces of domestic ruminants.

The objective of this study was to conduct a systematic review and meta‐analysis of the published literature to evaluate the efficacy of vaccines in reducing faecal shedding of Escherichia coli O157 in ruminants. A systematic search of eight databases and land‐grant university research reports using an algorithm adapted from a previous systematic review of pre‐harvest interventions against E. coli O157 was conducted to locate all reports of in vivo trials of E. coli O157 vaccines in ruminants published between 1990 and 2010. All located references were screened by two independent reviewers, and data were extracted from all relevant papers, with treatment effect measured in odds ratios. For trials with a faecal prevalence outcome that did not involve mixing of treated and untreated cattle in the same pen, efficacy was explored using random‐effects meta‐analysis. Funnel plots were used to evaluate publication bias, and random‐effects meta‐regression was performed to explore heterogeneity. The search located 20 relevant manuscripts which detailed 24 trials and 46 treatment comparisons; all but one trial involved cattle. There were 9 deliberate challenge trials (19 comparisons), and 15 natural exposure trials (27 comparisons). For Type III protein vaccines, there were 9 natural exposure trials detailing 17 comparisons, and meta‐analysis of 8 comparisons revealed that vaccine treatment resulted in a statistically significant reduction in E. coli O157 faecal prevalence [odds ratio (OR) = 0.38, 95% confidence interval (CI) = 0.29, 0.51]. Siderophore receptor and porin protein (SRP) vaccines (three trials/four comparisons) also reduced faecal prevalence (OR = 0.42, 95% CI = 0.20, 0.61); however, none of the bacterin vaccine trials (n = 3, six comparisons) resulted in a statistically significant reduction in prevalence. The results suggest that Type III protein and SRP vaccines significantly reduce faecal shedding in cattle; however, caution should be taken in interpreting the results because of the heterogeneity in the results.

Feeding management practices and feed characteristics associated with Salmonella prevalence in live and slaughtered market-weight finisher swine: A systematic review and summation of evidence from 1950 to 2005

This review summarizes evidence for associations between Salmonella prevalence in market-weight swine and changes in feeding management practices or feed characteristics. A systematic review of the topic was conducted with the goal of minimizing the impact of bias on the review conclusions. Potential interventions included feed withdrawal from swine prior to slaughter, feed acidification, heat treatment of feed, pelletized feed versus mash, course versus fine grind, and wet versus dry feeds. In the reviewed literature, Salmonella prevalence was measured either by culture or by the presence of antibodies to Salmonella. The evidentiary value of studies was assessed, and studies that failed to meet predetermined standards were excluded. 7694 potentially relevant references were identified by an extensive literature search; however, 2623 references that were not published in English were excluded, because funds for translation were not available. Of the remaining references, only 277 were considered relevant to the review topic by two independent reviewers, and assessed for methodological quality. During quality assessment, 233 references were excluded because they failed to report design features that limit the introduction of bias or were conducted in a non-target population such as gnotobiotic, neonatal, nursery, or recently weaned pigs and sows. Forty-four publications passed the quality assessment conducted by 2 independent reviewers, but only 15 of the 44 publications reported studies that tested hypotheses associated with feeding management practices and feed characteristics and Salmonella prevalence in market-weight swine. The most common study design was cross-sectional (7/15). The included studies failed to provide strong evidence of an association between any of the potential interventions and Salmonella prevalence, due to the potential for confounding, and the failure to document temporal association between the intervention and Salmonella prevalence. The strongest evidence of an association was found for feed form, i.e. the use of non-pelleted may be potential interventions associated with reduced Salmonella prevalence. The uncertainty is primarily based on studies containing moderate to low evidentiary value or insufficient numbers of tested individuals, resulting in a low degree of confidence that results could be extrapolated to the target population. Therefore, the conclusion of the review is that there should be a low level of comfort among qualified scientists that the claimed association between non-pelleted feed and reduced Salmonella prevalence is scientifically valid. There is no strong evidence regarding associations between presence of Salmonella and the other feed characteristics examined.

Methodological quality and completeness of reporting in clinical trials conducted in livestock species

Randomized controlled trials (RCTs) are the gold standard for evaluating efficacy of treatments under real world conditions and, as such, it is important that they are conducted with methodological rigour to prevent biased results. Many medical journals have adopted a standard checklist for reporting of RCTs, the CONSORT statement. The objective of this study was to evaluate clinical trials in livestock populations to assess methodological quality and completeness of reporting and to investigate the association between these criteria and treatment effects. A total of 100 clinical trials published between 2006 and 2008 in the English language were randomly selected. For each trial, 2 reviewers independently completed a checklist based on the CONSORT statement and a different 2 reviewers completed a standard template describing the outcomes used and the statistical significance of all reported treatment effects. Disagreements among reviewers were resolved by consensus. The results showed that there were substantive deficiencies in the reporting of many of trial features, both related to methodological quality and completeness of reporting. Details on key features such as randomization, double blinding, and the number of subjects lost to follow-up were reported in only 67, 4, and 62% of trials, respectively. Reporting of random allocation to treatment group was associated with a lower proportion of positive treatments effects within trials, as was reporting of inclusion/exclusion criteria for study subjects, details on the intervention, animal signalment, significance tests of baseline differences for at least one variable, and the methods used to measure all outcomes. The results suggest that there are deficiencies in the current reporting of important features of RCTs conducted in livestock species and that these deficiencies may be associated with biased treatment effects. The creation and adoption of standards for trial reporting in livestock could aid authors, reviewers, and editors in ensuring that necessary trial details are reported in all published trials.

Prevalence and Serovars of Salmonella in the Feces of Free-Ranging White-Tailed Deer (Odocoileus virginianus) in Nebraska

To determine the prevalence and serovars of Salmonella in free-ranging deer, we cultured feces from white-tailed deer (Odocoileus virginianus) harvested by hunters during a regular firearm season in southeastern Nebraska (USA). We recovered Salmonella from 5 (1%; 95% confidence interval: 0.37–2.20%) of 500 samples and identified four different Salmonella enterica serovars [Litch-field (1), Dessau (1), Infantis (2), and Enteritidis (1)]. Although the prevalence of Salmonella in free-ranging deer appears to be low, the serovars recovered are known to be pathogenic to humans and animals.

The REFLECT Statement: Reporting Guidelines for Randomized Controlled Trials in Livestock and Food Safety: Explanation and Elaboration

Concerns about the completeness and accuracy of reporting of randomized clinical trials (RCTs) and the impact of poor reporting on decision making have been documented in the medical field over the past several decades. Experience from RCTs in human medicine would suggest that failure to report critical trial features can be associated with biased estimated effect measures, and there is evidence to suggest that similar biases occur in RCTs conducted in livestock populations. In response to these concerns, standardized guidelines for reporting RCTs were developed and implemented in human medicine. The Consolidated Standards of Reporting Trials (CONSORT) statement was first published in 1996, with a revised edition published in 2001. The CONSORT statement consists of a 22‐item checklist for reporting a RCT and a flow diagram to follow the number of participants at each stage of a trial. An explanation and elaboration document not only defines and discusses the importance of each of the items, but also provides examples of how this information could be supplied in a publication. Differences between human and livestock populations necessitate modifications to the CONSORT statement to maximize its usefulness for RCTs involving livestock. These have been addressed in an extension of the CONSORT statement titled the REFLECT statement: Methods and processes of creating reporting guidelines for randomized control trials for livestock and food safety. The modifications made for livestock trials specifically addressed the common use of group housing and group allocation to intervention in livestock studies; the use of deliberate challenge models in some trials and the common use of non‐clinical outcomes, such as contamination with a foodborne pathogen. In addition, the REFLECT statement for RCTs in livestock populations proposed specific terms or further clarified terms as they pertained to livestock studies.

Presence of glutamine at position 74 of pocket 4 in the BoLA-DR antigen binding groove is associated with occurrence of clinical mastitis caused by Staphylococcus species

Potential relationships between amino acid motifs in the antigen binding groove of various alleles of the bovine major histocompatibility complex DR (BoLA-DR) molecule and occurrence of clinical mastitis caused by Staphylococcus species (non-Staphylococcus aureus) were investigated in a case-control study. A significant association (P< or =0.05) was detected between the presence of glutamic acid at position beta 74 and occurrence of mastitis caused by Staphylococcus spp. with a relative risk of 11. This motif is present in BoLA-DRB3.2*22, *23 and *24 alleles. Presence of a positively charged residue (arginine or lysine) at position 13 also showed a tendency (P< o r=0.1) towards an association with a higher risk of clinical mastitis caused by the same bacteria. This motif is present in BoLA-DRB3.2*23 and *8 alleles. Similarly, presence of arginine at position beta 71 (present in alleles *23 and *22) was associated with occurrence of this disease. These positions (beta 13, beta 71 and beta 74) form pocket 4 of the antigen binding groove, which plays an instrumental role in antigen binding and recognition by T-lymphocytes. Thus, it can be concluded that pocket 4 of the BoLA-DR molecule is involved in conferring susceptibility to clinical mastitis caused by Staphylococcus spp.