Matthew J. Denwood

Anthelmintic resistance to ivermectin and moxidectin in gastrointestinal nematodes of cattle in Europe.

Anthelmintic resistance has been increasingly reported in cattle worldwide over the last decade, although reports from Europe are more limited. The objective of the present study was to evaluate the efficacy of injectable formulations of ivermectin and moxidectin at 0.2 mg per kg bodyweight against naturally acquired gastro-intestinal nematodes in cattle. A total of 753 animals on 40 farms were enrolled in Germany (12 farms), the UK (10 farms), Italy (10 farms), and France (8 farms). Animals were selected based on pre-treatment faecal egg counts and were allocated to one of the two treatment groups. Each treatment group consisted of between 7 and 10 animals. A post-treatment faecal egg count was performed 14 days (±2 days) after treatment. The observed percentage reduction was calculated for each treatment group based on the arithmetic mean faecal egg count before and after treatment. The resistance status was evaluated based on the reduction in arithmetic mean faecal egg count and both the lower and upper 95% confidence limits. A decreased efficacy was observed in half or more of the farms in Germany, France and the UK. For moxidectin, resistance was confirmed on 3 farms in France, and on 1 farm in Germany and the UK. For ivermectin, resistance was confirmed on 3 farms in the UK, and on 1 farm in Germany and France. The remaining farms with decreased efficacy were classified as having an inconclusive resistance status based on the available data. After treatment Cooperia spp. larvae were most frequently identified, though Ostertagia ostertagi was also found, in particular within the UK and Germany. The present study reports lower than expected efficacy for ivermectin and moxidectin (based on the reduction in egg excretion after treatment) on European cattle farms, with confirmed anthelmintic resistance on 12.5% of the farms.

An ecological approach to assessing the epidemiology of antimicrobial resistance in animal and human populations

We examined long-term surveillance data on antimicrobial resistance (AMR) in Salmonella Typhimurium DT104 (DT104) isolates from concurrently sampled and sympatric human and animal populations in Scotland. Using novel ecological and epidemiological approaches to examine diversity, and phenotypic and temporal relatedness of the resistance profiles, we assessed the more probable source of resistance of these two populations. The ecological diversity of AMR phenotypes was significantly greater in human isolates than in animal isolates, at the resolution of both sample and population. Of 5200 isolates, there were 65 resistance phenotypes, 13 unique to animals, 30 unique to humans and 22 were common to both. Of these 22, 11 were identified first in the human isolates, whereas only five were identified first in the animal isolates. We conclude that, while ecologically connected, animals and humans have distinguishable DT104 communities, differing in prevalence, linkage and diversity. Furthermore, we infer that the sympatric animal population is unlikely to be the major source of resistance diversity for humans. This suggests that current policy emphasis on restricting antimicrobial use in domestic animals may be overly simplistic. While these conclusions pertain to DT104 in Scotland, this approach could be applied to AMR in other bacteria–host ecosystems.

Comparison of three alternative methods for analysis of equine Faecal Egg Count Reduction Test data.

The Faecal Egg Count Reduction Test (FECRT) is the most widely used method of assessing the efficacy of anthelmintics, and is the only in vivo technique currently approved for use with horses. Equine Faecal Egg Count (FEC) data are frequently characterised by a low mean, high variability, small sample size and frequent zero count observations. Accurate analysis of the data therefore depends on the use of an appropriate statistical technique. Analyses of simulated FECRT data by methods based on calculation of the empirical mean and variance, non-parametric bootstrapping, and Markov chain Monte Carlo (MCMC) are compared. The MCMC method consistently outperformed the other methods, independently of the distribution from which the data were generated. Bootstrapping produced notional 95% confidence intervals containing the true parameter as little as 40% of the time with sample sizes of less than 50. Analysis of equine FECRT data yielded inconclusive results in 53 of 63 (84%) datasets, suggesting that the routine use of prior sample size calculations should be adopted to ensure sufficient data are collected. The authors conclude that computationally intensive parametric methods such as MCMC be used for analysis of FECRT data with sample sizes of less than 50, in order to avoid erroneous inference about the true efficacy of anthelmintics in the field.

The distribution of the pathogenic nematode Nematodirus battus in lambs is zero-inflated

Understanding the frequency distribution of parasites and parasite stages among hosts is essential for efficient experimental design and statistical analysis, and is also required for the development of sustainable methods of controlling infection. Nematodirus battus is one of the most important organisms that infect sheep but the distribution of parasites among hosts is unknown. An initial analysis indicated a high frequency of animals without N. battus and with zero egg counts, suggesting the possibility of a zero-inflated distribution. We developed a Bayesian analysis using Markov chain Monte Carlo methods to estimate the parameters of the zero-inflated negative binomial distribution. The analysis of 3000 simulated data sets indicated that this method out-performed the maximum likelihood procedure. Application of this technique to faecal egg counts from lambs in a commercial upland flock indicated that N. battus counts were indeed zero-inflated. Estimating the extent of zero-inflation is important for effective statistical analysis and for the accurate identification of genetically resistant animals.

Quantifying the sources of variability in equine faecal egg counts: Implications for improving the utility of the method

The faecal egg count (FEC) is the most widely used means of quantifying the nematode burden of horses, and is frequently used in clinical practice to inform treatment and prevention. The statistical process underlying the FEC is complex, comprising a Poisson counting error process for each sample, compounded with an underlying continuous distribution of means between samples. Being able to quantify the sources of variability contributing to this distribution of means is a necessary step towards providing estimates of statistical power for future FEC and FECRT studies, and may help to improve the usefulness of the FEC technique by identifying and minimising unwanted sources of variability. Obtaining such estimates require a hierarchical statistical model coupled with repeated FEC observations from a single animal over a short period of time. Here, we use this approach to provide the first comparative estimate of multiple sources of within-horse FEC variability. The results demonstrate that a substantial proportion of the observed variation in FEC between horses occurs as a result of variation in FEC within an animal, with the major sources being aggregation of eggs within faeces and variation in egg concentration between faecal piles. The McMaster procedure itself is associated with a comparatively small coefficient of variation, and is therefore highly repeatable when a sufficiently large number of eggs are observed to reduce the error associated with the counting process. We conclude that the variation between samples taken from the same animal is substantial, but can be reduced through the use of larger homogenised faecal samples. Estimates are provided for the coefficient of variation (cv) associated with each within animal source of variability in observed FEC, allowing the usefulness of individual FEC to be quantified, and providing a basis for future FEC and FECRT studies.

The effectiveness of faecal removal methods of pasture management to control the cyathostomin burden of donkeys

BackgroundThe level of anthelmintic resistance within some cyathostomin parasite populations has increased to the level where sole reliance on anthelmintic-based control protocols is not possible. Management-based nematode control methods, including removal of faeces from pasture, are widely recommended for use in association with a reduction in anthelmintic use to reduce selection pressure for drug resistance; however, very little work has been performed to quantitatively assess the effectiveness of such methods.MethodsWe analysed data obtained from 345 donkeys at The Donkey Sanctuary (Devon, UK), managed under three different pasture management techniques, to investigate the effectiveness of faeces removal in strongyle control in equids. The management groups were as follows: no removal of faeces from pasture, manual, twice-weekly removal of faeces from pasture and automatic, twice-weekly removal of faeces from pasture (using a mechanical pasture sweeper). From turn-out onto pasture in May, monthly faecal egg counts were obtained for each donkey and the dataset subjected to an auto regressive moving average model.ResultsThere was little to no difference in faecal egg counts between the two methods of faecal removal; both resulted in significantly improved cyathostomin control compared to the results obtained from the donkeys that grazed pasture from which there was no faecal removal.ConclusionsThis study represents a valuable and unique assessment of the effectiveness of the removal of equine faeces from pasture, and provides an evidence base from which to advocate twice-weekly removal of faeces from pasture as an adjunct for equid nematode control. Widespread adoption of this practice could substantially reduce anthelmintic usage, and hence reduce selection pressure for nematode resistance to the currently effective anthelmintic products.

Systems approaches to animal disease surveillance and resource allocation: methodological frameworks for behavioral analysis.

While demands for animal disease surveillance systems are growing, there has been little applied research that has examined the interactions between resource allocation, cost-effectiveness, and behavioral considerations of actors throughout the livestock supply chain in a surveillance system context. These interactions are important as feedbacks between surveillance decisions and disease evolution may be modulated by their contextual drivers, influencing the cost-effectiveness of a given surveillance system. This paper identifies a number of key behavioral aspects involved in animal health surveillance systems and reviews some novel methodologies for their analysis. A generic framework for analysis is discussed, with exemplar results provided to demonstrate the utility of such an approach in guiding better disease control and surveillance decisions.

Associations between the Presence of Virulence Determinants and the Epidemiology and Ecology of Zoonotic Escherichia coli

ABSTRACT The severity of human infection with pathogenic Escherichia coli depends on two major virulence determinants (eae and stx) that, respectively, produce intimin and Shiga toxin. In cattle, both may enhance colonization, but whether this increases fitness by enhancing cattle-to-cattle transmission in the field is unknown. In E. coli O157, the almost uniform presence of the virulence determinants in cattle isolates prevents comparative analysis. The availability to this study of extensive non-O157 E. coli data, with much greater diversity in carriage of virulence determinants, provides the opportunity to gain insight into their potential impact on transmission. Dynamic models were used to simulate expected prevalence distributions for serogroups O26 and O103. Transmission parameters were estimated by fitting model outputs to prevalence data from Scottish cattle using a Bayesian Markov chain Monte Carlo (MCMC) approach. Despite similar prevalence distributions for O26 and O103, their transmission dynamics were distinct. Serogroup O26 strains appear well adapted to the cattle host. The dynamics are characterized by a basic reproduction ratio (R0) of >1 (allowing sustained cattle-to-cattle transmission), a relatively low transmission rate from environmental reservoirs, and substantial association with eae on transmission. The presence of stx2 was associated with reduced transmission. In contrast, serogroup O103 appears better adapted to the noncattle environment, characterized by an R0 value of <1 for plausible test sensitivities, a significantly higher transmission rate from noncattle sources than serogroup O26, and an absence of fitness benefits associated with the carriage of eae. Thus, the association of eae with enhanced transmission depends on the E. coli serogroup. Our results suggest that the capacity of E. coli strains to derive fitness benefits from virulence determinants influences the prevalence in the cattle population and the ecology and epidemiology of the host organism.

Comparison of recording of pericarditis and lung disorders at routine meat inspection with findings at systematic health monitoring in Danish finisher pigs

BackgroundThe use of secondary data is widespread in a range of surveillance and monitoring applications because of the low cost and high availability associated with this form of data. However, as they are often collected for quite unrelated purposes, they are not necessarily fit for the new purpose that is required of them. Routine meat inspection data were originally collected with the purpose of safeguarding food, but have been re-tasked to also include animal welfare assessment. The objective of the present study was to compare the recording of pericarditis, pleuritis and lungs with lesions at routine meat inspection (RMI) with those performed at systematic health monitoring (SHM) in Danish pigs at slaughter, in order to assess the usefulness of RMI for monitoring the prevalence of these diseases. Data originating from 165 Danish pig herds were collected in the period September 2011 to November 2013. From each herd, a batch consisting of all pigs slaughtered on a specific day from a specific farm were included as the RMI data, while lungs and hearts sampled from the batches were used for the SHM. The RMI data and SHM data included recordings related to a) chronic pericarditis, b) chronic pleuritis and c) lung lesions. The proportion of carcases with a specific disease recording was estimated for each batch of pigs, and linear regression was used to relate the RMI-proportion to the SHM-proportion for the conditions mentioned above.ResultsThe coefficients of determination (R2) were estimated as R2,pericarditis = 0.16; R2,pleuritis = 0.67; R2,lungs with lesions = 0.40. R2,pericarditis changed to 0.42 when the regression analysis included inspection type at the abattoir (with purely visual inspection of the hearts versus traditional inspection including an incision into the heart).ConclusionsOverall, the results suggest that the correlation between findings at RMI and SHM was moderate for pleuritis and lungs with lesions, but poor for pericarditis. The latter could partly be explained by the type of meat inspection conducted at the abattoir. We conclude that caution should be used whenever RMI data are used for purposes other than those for which they were originally intended.

An Invasive Mammal (the Gray Squirrel, Sciurus carolinensis) Commonly Hosts Diverse and Atypical Genotypes of the Zoonotic Pathogen Borrelia burgdorferi Sensu Lato.

ABSTRACT Invasive vertebrate species can act as hosts for endemic pathogens and may alter pathogen community composition and dynamics. For the zoonotic pathogen Borrelia burgdorferi sensu lato, the agent of Lyme borreliosis, recent work shows invasive rodent species can be of high epidemiological importance and may support host-specific strains. This study examined the role of gray squirrels (Sciurus carolinensis) (n = 679), an invasive species in the United Kingdom, as B. burgdorferi sensu lato hosts. We found that gray squirrels were frequently infested with Ixodes ricinus, the main vector of B. burgdorferi sensu lato in the United Kingdom, and 11.9% were infected with B. burgdorferi sensu lato. All four genospecies that occur in the United Kingdom were detected in gray squirrels, and unexpectedly, the bird-associated genospecies Borrelia garinii was most common. The second most frequent infection was with Borrelia afzelii. Genotyping of B. garinii and B. afzelii produced no evidence for strains associated with gray squirrels. Generalized linear mixed models (GLMM) identified tick infestation and date of capture as significant factors associated with B. burgdorferi sensu lato infection in gray squirrels, with infection elevated in early summer in squirrels infested with ticks. Invasive gray squirrels appear to become infected with locally circulating strains of B. burgdorferi sensu lato, and further studies are required to determine their role in community disease dynamics. Our findings highlight the fact that the role of introduced host species in B. burgdorferi sensu lato epidemiology can be highly variable and thus difficult to predict.