Free access
Issue
Vet. Res.
Volume 36, Number 4, July-August 2005
Page(s) 545 - 555
DOI http://dx.doi.org/10.1051/vetres:2005014
How to cite this article Vet. Res. (2005) 545-555
Vet. Res. 36 (2005) 545-555
DOI: 10.1051/vetres:2005014

Discrepancies between the isolation of Salmonella from mesenteric lymph nodes and the results of serological screening in slaughter pigs

Nathalie Nolleta, b, Dominiek Maesb, Luc Duchateauc, Veerle Hautekietd, Kurt Houfa, Jan Van Hoofa, Lieven De Zutteraa, Aart De Kruifb and Rony Geersd

a  Department of Veterinary Public Health and Food Safety, Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, 9820 Merelbeke, Belgium
b  Department of Reproduction, Obstetrics and Herd Health, Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, 9820 Merelbeke, Belgium
c  Department of Physiology, Biochemistry and Biometrics, Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, 9820 Merelbeke, Belgium
d  Laboratory for Quality Care in Animal Production, Zootechnical Centre, K.U. Leuven, Bijzondere Weg 12, 3360 Lovenjoel, Belgium

(Received 8 July 2004; accepted 9 November 2004)

Abstract - Most Salmonella control programmes are based on serological testing in the slaughterhouse. However, from a point of view of carcass contamination, it is rather the presence of Salmonella spp. in the animal at the time of slaughter that is important. The aim of this cross-sectional study was to investigate the possible discrepancies between the isolation of Salmonella spp. in the mesenteric lymph nodes and the results of serological screening. In total, 1821 fattening pigs originating from 60 Belgian farrow-to-finish herds were sampled in the slaughterhouse. The serum samples were analysed using an indirect mix-ELISA for the presence of Salmonella antibodies and evaluated at 3 cut-off values namely 10, 20, and 40% Optical Density (OD). All mesenteric lymph node samples were submitted to qualitative Salmonella isolation and a representative number of isolates was serotyped. From each herd, 30 animals were screened both serologically and bacteriologically and the herd was considered as positive when at least one sample was positive. At the herd level, 83.6% (cut-off OD 40%) to 100.0% (cut-off OD 10%) of the herds from which Salmonella had been isolated were evaluated as seropositive. At the individual level, only 34.5% (cut-off OD 40%) to 82.8% (cut-off OD 10%) of the animals from which Salmonella had been isolated were seropositive. Overall, a weak agreement was found between bacteriology and serology for Salmonella diagnosis. If pig herds are categorised using serological tests in the slaughterhouse, one should be aware of the fact that slaughter pigs can still harbour Salmonella spp. in the mesenteric lymph nodes, without being detected in serological tests. The cut-off value used to evaluate a sample as serologically positive and the number of samples per herd are of major importance to classify herds correctly in order to protect human health.


Key words: slaughter pig / Salmonella / bacteriology / serology

Corresponding author: Nathalie Nollet nathalie.nollet@UGent.be

© INRA, EDP Sciences 2005