Prevalence of livestock-associated MRSA on Dutch broiler farms and in people living and/or working on these farms.

This study aimed to determine the prevalence and risk factors for methicillin-resistant Staphylococcus aureus (MRSA) on 50 Dutch broiler farms. Of 145 persons living and/or working on these farms, eight tested positive for MRSA (5.5%). Investigation of 250 pooled throat samples of broilers and 755 dust samples resulted in four farms where MRSA-positive samples were present (8.0%). All isolates belonged to the CC398 complex. Living and/or working on a MRSA-positive farm was a risk for MRSA carriage; 66.7% of people on positive farms were MRSA positive vs. 1.5% on negative farms (P<0.0001). Due to the low number of positive farms and persons, and high similarity in farm management, it was impossible to draw statistically valid conclusions on other risk factors. For broiler farming, both farm and human MRSA prevalence seem much lower than for pig or veal farming. However, MRSA carriage in people living and/or working on broiler farms is higher compared to the general human population in The Netherlands (5.5% vs. <0.1%). As broiler husbandry systems are not unique to The Netherlands, this might imply that people in contact with live broilers are at risk for MRSA carriage worldwide.

Community incidence of pathogen-specific gastroenteritis: reconstructing the surveillance pyramid for seven pathogens in seven European Union member states.

By building reconstruction models for a case of gastroenteritis in the general population moving through different steps of the surveillance pyramid we estimated that millions of illnesses occur annually in the European population, leading to thousands of hospitalizations. We used data on the healthcare system in seven European Union member states in relation to pathogen characteristics that influence healthcare seeking. Data on healthcare usage were obtained by harmonized cross-sectional surveys. The degree of under-diagnosis and underreporting varied by pathogen and country. Overall, underreporting and under-diagnosis were estimated to be lowest for Germany and Sweden, followed by Denmark, The Netherlands, UK, Italy and Poland. Across all countries, the incidence rate was highest for Campylobacter spp. and Salmonella spp. Incidence estimates resulting from the pyramid reconstruction approach are adjusted for biases due to different surveillance systems and are therefore a better basis for international comparisons than reported data.

Constructing naive Bayesian classifiers for veterinary medicine: a case study in the clinical diagnosis of classical swine fever.

For diseases of which the clinical diagnosis is uncertain, naive Bayesian classifiers can be of assistance to the veterinary practitioner. These simple probabilistic models have proven to be very powerful for solving classification problems in a variety of domains, but are not yet widely applied within the veterinary domain. In this paper, naive Bayesian classifiers and methods for their construction are reviewed. We demonstrate how to construct full and selective classifiers from a data set and how to build such classifiers from information in the literature. As a case study, naive Bayesian classifiers to discriminate between classical swine fever (CSF)-infected and non-infected pig herds were constructed from data collected during the 1997/1998 CSF epidemic in the Netherlands. The resulting classifiers were studied in terms of their accuracy and compared with the optimally efficient diagnostic rule that was reported earlier by Elbers et al. (2002). The classifiers were found to have accuracies within the range of 67-70% and performed comparable to or even better than the diagnostic rule on the available data. In contrast with the diagnostic rule, the classifiers had the advantage of taking both the presence and the absence of particular clinical signs into account, which resulted in more discriminative power. These results indicate that naive Bayesian classifiers are promising tools for solving diagnostic problems in the veterinary field.

Prevalence of livestock-associated MRSA in broiler flocks and risk factors for slaughterhouse personnel in The Netherlands.

To determine methicillin-resistant Staphylococcus aureus (MRSA) carriage in poultry and slaughterhouse personnel, 40 Dutch broiler flocks, in six slaughterhouses and 466 personnel were sampled. Of the employees, 26 were positive (5.6%), indicating a higher risk of exposure when compared to the general Dutch population (0.1%). This risk was significantly higher for personnel having contact with live animals (5.2%) - especially hanging broilers on the slaughterline (20.0%) - than for all other personnel (1.9%). Conventional electric stunning conferred a significantly higher risk of MRSA carriage for employees than CO2 stunning (9.7% vs. 2.0%). A total of 405 broilers were sampled upon their arrival at the slaughterhouse, of which 6.9% were positive. These broilers originated from 40 Dutch slaughter flocks of which 35.0% were positive. MRSA contamination in the different compartments of slaughterhouses increased during the production day, from 8% to 35%. Of the 119 MRSA isolates, predominantly livestock-associated MRSA ST398 was found, although 27.7% belonged to ST9 (spa type t1430). There is an increased risk of MRSA carriage in personnel working at broiler slaughterhouses, particularly those having contact with live animals.

Dietary specific antibodies in spray-dried immune plasma prevent enterotoxigenic Escherichia coli F4 (ETEC) post weaning diarrhoea in piglets.

In order to establish the mechanism of spray dried plasma powder (SDPP) in improving pig health and performance, a diet containing either 8% SDPP, spray dried immune plasma powder (SDIPP), or control protein (soybean and whey) ration was fed to piglets in an experimental model of enterotoxigenic Escherichia coli F4 (ETEC) post-weaning diarrhoea (PWD). SDIPP was obtained from pigs immunized with a vaccine containing ETEC fimbrial subunit F4 and heat-labile toxin (LT), and SDPP from non-immunized controls. Average daily growth (ADG) was determined, and daily samples of rectal faeces were assessed for diarrhoea (as percentage of dry matter), and ETEC excretion (in CFU/g). SDPP and SDIPP significantly (p<0.05) reduced diarrhoea, and SDIPP significantly reduced ETEC excretion. ADG was not significantly (p>0.05) affected. After the experiment, 30% of piglets tested F4 receptor positive (F4R+). A significant correlation between F4R status and morbidity was found. In F4R+ animals, SDIPP significantly improved diarrhoea and ADG, and decreased ETEC excretion, and SDPP significantly improved diarrhoea and ADG. Surprisingly, SDPP reduced diarrhoea in F4R+ animals without significant reduction of ETEC excretion, which is most likely related to the presence of anti-LT antibodies in SDPP. The results show that oral protection against ETEC by SDPP is attributable to spontaneous antibodies, in this case anti-LT antibodies. Furthermore, the results indicate that the combination of anti-LT and anti-F4 antibodies as in SDIPP is most effective in ETEC prevention. Finally, the F4R distribution in the herd should be taken into account to correctly assess efficacy.

Classification of temporal profiles of F4+ E. coli shedding and faecal dry matter in experimental post-weaning diarrhoea of pigs.

Enterotoxigenic F4+ Escherichia coli can colonize the intestine of pigs and cause diarrhoea. Our primary goal was to find a discriminant rule to discriminate between F4+ E. coli shedding profiles as this may reflect differences in the infectiousness of pigs. Our secondary goal was to find a discriminant rule to discriminate between diarrhoeic and non-diarrhoeic pigs. Repeated measurements (bacterial shedding and percentage dry matter of faeces) were taken of 74 weaned pigs that were infected experimentally with F4+ E. coli. These measurements were summarized into two new variables by means of a principal components analysis. Discriminant rules were derived based on these summary variables by fitting a mixture of normal distributions. Finally, the association between the classifications (as derived from the discriminant rules) and the occurrence in the pigs of the F4 receptor, an adhesion site for F4+ E. coli, was studied. We found that only the classification based on bacterial shedding allowed us to distinguish two significantly different groups of pigs (high and low shedders). Presence of the F4 receptor was associated strongly with pigs being high shedders.

Transmission of F4+ E. coli in groups of early weaned piglets.

The aim of this study was to estimate transmission parameters of enterotoxigenic F4+ Escherichia coli F4 (F4+ E. coli) in groups of early weaned piglets with F4-receptor-positive (F4R+) and F4-receptor-negative piglets (F4R-). Transmission of F4+ E. coli was quantified in four heterogeneous groups of F4R+ and F4R- piglets. Infectiousness was determined by the number of F4+ E. coli/g faeces shed during 8 days. Transmission parameters were estimated using generalized linear models assuming a stochastic SIR model. F4R+ piglets were found to be more susceptible than F4R- piglets, but F4R+ and F4R- piglets were not different in infectiousness. The reproduction ratios for homogeneous F4R+ and F4R- populations were estimated as 6.37 (95% CI 1.89-21.48) and 0.02 (95% CI 0.00-1.13) respectively. The implication of these results is that in order to prevent major outbreaks, the fraction of F4R+ piglets should be small (approximately 10% or less). Therefore, selective breeding programmes could contribute to reducing F4+ E. coli-related diarrhoea and transmission.

Estimating transmission parameters of F4+ E. coli for F4-receptor-positive and -negative piglets: one-to-one transmission experiment.

F4+ Escherichia coli is an important agent of post-weaning diarrhoea in piglets. Piglets that express an adhesion site for F4+ E. coli in their small intestine (F4R+) shed higher numbers of F4+ E. coli than piglets lacking this site (F4R-). We hypothesized that F4R+ piglets are more infectious and more susceptible for F4+ E. coli. This implies that in populations with F4R+ and F4R- piglets, the transmission would be dependent on the frequency of both types of animals. To quantify the difference in infectiousness and susceptibility, a one-to-one transmission experiment was performed with 20 pairs consisting of one inoculated and one contact piglet. Based on the contact infections observed, transmission parameters were estimated with generalized linear models. F4R+ piglets were infectious for other piglets and the reproduction ratio (R0) for homogeneous F4R+ populations, that is the average number of secondary infections that one F4R+ pig will cause during its entire infectious period in a population of susceptible F4R+ individuals only, was estimated as 7.1. F4R+ piglets were more susceptible than F4R- piglets and reducing the fraction of F4R+ piglets of a population will reduce transmission. It was calculated that in order to prevent major outbreaks of F4+ E. coli (R0 < 1), the fraction of F4R+ piglets must be lower than 0.14.

The morphogenesis of Ascaris suum to the infective third-stage larvae within the egg.

Studies of the morphology of Ascaris suum larvae developing in the egg during embryonation in vitro at room temperature showed that 2 molts take place within the egg. The first larval stage (L1) appeared in the egg after 17-22 days of cultivation, the first molt to the second larval stage (L2) took place from day 22 to day 27, and the second molt to the third larval stage (L3) started on day 27 and continued during the 60-day observation period. Infectivity of the eggs was studied by oral egg inoculation in mice and showed that the L3 are the infective stage for mice. Molting to the L3 stage occurs gradually over a period of 2-6 wk, and it is recommended to have an additional maturation period so the infectivity of an egg batch may reach maximum level.