An intercomparison study of ELISAs for the detection of porcine reproductive and respiratory syndrome virus - evaluating six conditionally dependent tests.

Latent class analysis is a widely used statistical method for evaluating diagnostic tests without any gold standard. It requires the results of at least two tests applied to the same individuals. Based on the resulting response patterns, the method estimates the test accuracy and the unknown disease status for all individuals in the sample. An important assumption is the conditional independence of the tests. If tests with the same biological principle are used, the assumption is not fulfilled, which may lead to biased results. In a recent publication, we developed a method that considers the dependencies in the latent class model and estimates all parameters using frequentist methods. Here, we evaluate the practicability of the method by applying it to the results of six ELISA tests for antibodies against the porcine reproductive and respiratory syndrome (PRRS) virus in pigs that generally follow the same biological principle. First, we present different methods of identifying suitable starting values for the algorithm and apply these to the dataset and a vaccinated subgroup. We present the calculated values of the test accuracies, the estimated proportion of antibody-positive animals and the dependency structure for both datasets. Different starting values led to matching results for the entire dataset. For the vaccinated subgroup, the results were more dependent on the selected starting values. All six ELISA tests are well suited to detect antibodies against PRRS virus, whereas none of the tests had the best values for sensitivity and specificity simultaneously. The results thus show that the method used is able to determine the parameter values of conditionally dependent tests with suitable starting values. The choice of test should be based on the general fit-for-purpose concept and the population under study.

Antibiotic resistance in Escherichia coli from pigs from birth to slaughter and its association with antibiotic treatment.

The purpose of this longitudinal study was to describe the occurrence of antibiotic resistance in faecal Escherichia coli isolated from pigs between birth and slaughter and its association with antibiotic treatment. Four objectives were addressed: comparison of antibiotic resistance in isolates from a) treated vs. non-treated pigs, b) follow-up vs. initial samples of treated and non-treated pigs, c) pigs receiving treatments via different administration routes and d) sows and their piglets. Each comparison addressed the following antibiotic groups used for treatment: beta-lactams, tetracyclines, polymyxins and macrolides, and the susceptibility of E. coli isolates to the respective agents: ampicillin, tetracycline, colistin and azithromycin. Between 2014 and 2016, 406 focal animals from 29 commercial breeding herds were followed from birth to the end of the relevant fattening periods. All antibiotic treatments in these pigs were documented. Faecal samples were collected from the focal pigs once while suckling, once after weaning and three times during fattening, and from their dams once around farrowing. Escherichia coli isolated from these samples was tested for antibiotic susceptibility. In total, 264 animals from 19 breeding herds were treated with an antibiotic at least once during their lifetime. Beta-lactams, tetracyclines and colistin were used most frequently. Piglets were treated individually by injection (n = 108 treatments) or via drench (9); weaners via feed (192) or water (56) and fatteners via feed (30) or injection (15). Resistance to ampicillin and tetracycline in E. coli was already common prior to antibiotic treatment. Resistance proportions were higher for beta-lactam-, tetracycline-, colistin- and macrolide-treated pigs compared to untreated pigs at different sampling periods (p < 0.05; Fisher's exact test). In the logistic analysis, the difference was confirmed for beta-lactam-treated vs. untreated pigs. In E. coli from macrolide-untreated pigs, resistance to azithromycin was more frequent compared to pre-treatment values. Route of application did not affect rates of antibiotic resistance in the logistic analysis even though Fisher's exact test indicated associations for beta-lactams (feed/water vs. injection), tetracyclines (feed/water vs. non-treatment) and macrolides (tulathromycin-injection vs. tylosin in feed). Piglets were more likely to carry an E. coli resistant to ampicillin or azithromycin if their dams did so as well. Our results suggest further research on resistance effects by administration routes is required. Reducing antibiotic resistance in sows might lead to a lower level of beta-lactam or macrolide-resistant E. coli among their progeny. To preserve treatment options for bacterial infections, antibiotic use should be restricted to necessary cases.

[Technopathies of the limbs in finishing pigs: risk factors, origin and impact on animal welfare - Study phase 1]. / Technopathien der Gliedmaßen bei Mastschweinen: Ursachen, Entstehung, Tierschutzrelevanz.

OBJECTIVE: The aim of the first part of the present study was to specify risk factors for the development of adventitious bursae on the limbs of weaning and finishing pigs. MATERIAL AND METHODS: In total, 192 pigs were examined weekly, recording the following parameters: general condition, number, size and localization of adventitious bursae on the limbs and sternum, gait and claws. RESULTS: Adventitious bursae can occur at 13 positions on the limbs or sternum. These adventitious bursae were already evident when pigs were moved to the nursery. The prevalence of adventitious bursae increased constantly from weaning to slaughter. At the age of 24 weeks, 97.8 % of all investigated pigs displayed adventitious bursae (aged 4 weeks: 25.5 %; aged 12 weeks: 67.6 %). Heavier pigs had significantly more and larger adventitious bursae than lighter pigs of the same age. Furthermore, heavier pigs retrieved feed from the automatic feeder less frequently but ate larger amounts each time. In addition, pigs with poorer gait displayed significantly more adventitious bursae. In 95.6 % of all investigated pigs, claw lesions were evident at slaughter. The general condition was unaffected by adventitious bursae. CONCLUSION AND CLINICAL RELEVANCE: Referring to the results of the present study and the general function of bursae protecting underlying structure against pressure, there is no indication that adventitious bursae affect the animal welfare in terms of the sensation of pain. Influenced by various factors, adventitious bursae develop with high prevalence and number per animal over the course of the life of pigs and can be described as a technopathy. Because of the exposure of adventitious bursae, there is a risk to become an ulcerated bursa of degree three in relation to injuries.