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Intestinal parasites in swine in the Nordic countries: multilevel modelling of Ascaris suum infections in relation to production factors

Published online by Cambridge University Press:  01 November 1999

A. ROEPSTORFF
Affiliation:
Danish Centre for Experimental Parasitology, Royal Veterinary and Agricultural University, Ridebanevej 3, DK-1870 Frederiksberg C, Copenhagen, Denmark
O. NILSSON
Affiliation:
The Swedish Animal Health Service, PO Box 9003, S-29109 Kristianstad, Sweden
C. J. O'CALLAGHAN
Affiliation:
Ecology and Epidemiology Group, Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, UK
A. OKSANEN
Affiliation:
Faculty of Veterinary Medicine, PO Box 57 (Hämeentie 57), 00014, University of Helsinki, FIN-00550 Helsinki, Finland
B. GJERDE
Affiliation:
Department of Pharmacology, Microbiology and Food Hygiene, Norwegian College of Veterinary Medicine, PO Box 8146 Dep, N-0033 Oslo, Norway
S. H. RICHTER
Affiliation:
Institute for Experimental Pathology, University of Iceland, Keldur v. Vesturlandsveg, IS-112, Reykjavik, Iceland
E. Ö. ORTENBERG
Affiliation:
Department of Parasitology, Statens Veterinärmedicinska Anstalt, Norra Ultuna 2, PO Box 7073, S-75007 Sweden
D. CHRISTENSSON
Affiliation:
Department of Parasitology, Statens Veterinärmedicinska Anstalt, Norra Ultuna 2, PO Box 7073, S-75007 Sweden
P. NANSEN
Affiliation:
Danish Centre for Experimental Parasitology, Royal Veterinary and Agricultural University, Ridebanevej 3, DK-1870 Frederiksberg C, Copenhagen, Denmark
L. ERIKSEN
Affiliation:
Danish Centre for Experimental Parasitology, Royal Veterinary and Agricultural University, Ridebanevej 3, DK-1870 Frederiksberg C, Copenhagen, Denmark Department of Clinical Studies, Royal Veterinary and Agricultural University, Dyrlægevej 88, DK-1870 Frederiksberg C, Copenhagen, Denmark
G. F. MEDLEY
Affiliation:
Danish Centre for Experimental Parasitology, Royal Veterinary and Agricultural University, Ridebanevej 3, DK-1870 Frederiksberg C, Copenhagen, Denmark Ecology and Epidemiology Group, Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, UK

Abstract

In Denmark, Finland, Iceland, Norway and Sweden, 413 sow herds were randomly selected for sampling. Faeces from pigs of 7 age groups/categories were examined for helminth eggs (11233 individual samples), and an accompanying questionnaire was completed at each visit. In total, 1138 pigs on 230 farms were found to be positive for Ascaris suum. Considerable differences in the occurrence of A. suum could be observed directly for several of 20 independent variables at the herd or category level. However, given that univariate analyses may be severely affected by confounding of covariates resulting in spurious inference, additional multivariate analyses were undertaken. An ordinary logistic regression on Ascaris positive/negative farms showed that Denmark had the highest frequency of infected herds, while Iceland and Finland had the lowest frequencies and that herds using ‘late weaning’ and ‘Class 2’ drugs (pyrantel, levamisole) were most often infected. Because many herds were found to be totally negative for A. suum, mixed hierarchical logistic-normal regression models (both the penalized quasi-likelihood and the Markov Chain Monte Carlo methods) were developed for both a full (all herds) and a reduced (the 230 infected herds) data set using either a cut-off of >0 eggs per gram (epg) or >200 epg to counter for false-positive egg counts. Estimates for identical models, but where the animal level variance was constrained to the binomial assumption, were also calculated. Significant covariates were robust to model development with ‘Age group’, ‘Country’, ‘Weaning age’, ‘Water system’ and simple interactions between the latter two and ‘Age group’ being significantly associated with the occurrence of A. suum, while all variables concerning anthelmintic drug, anthelmintic strategy, floor type, bedding, dung removal, washing and disinfection were not. These findings are discussed in the light of the complex relationship between A. suum and its pig host.

Type
Research Article
Copyright
1999 Cambridge University Press

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