title: Evaluation of a blocking ELISA for the detection of antibodies against Lawsonia intracellularis in pig sera.
abstract: BACKGROUND
  Lawsonia intracellularis is a common cause of chronic diarrhoea and poor performance in young growing pigs. Diagnosis of this obligate intracellular bacterium is based on the demonstration of the microbe or microbial DNA in tissue specimens or faecal samples, or the demonstration of L. intracellularis-specific antibodies in sera. The aim of the present study was to evaluate a blocking ELISA in the detection of serum antibodies to L. intracellularis, by comparison to the previously widely used immunofluorescent antibody test (IFAT).
  
  
  METHODS
  Sera were collected from 176 pigs aged 8-12 weeks originating from 24 herds with or without problems with diarrhoea and poor performance in young growing pigs. Sera were analyzed by the blocking ELISA and by IFAT. Bayesian modelling techniques were used to account for the absence of a gold standard test and the results of the blocking ELISA was modelled against the IFAT test with a "2 dependent tests, 2 populations, no gold standard" model.
  
  
  RESULTS
  At the finally selected cut-off value of percent inhibition (PI) 35, the diagnostic sensitivity of the blocking ELISA was 72% and the diagnostic specificity was 93%. The positive predictive value was 0.82 and the negative predictive value was 0.89, at the observed prevalence of 33.5%.
  
  
  CONCLUSIONS
  The sensitivity and specificity as evaluated by Bayesian statistic techniques differed from that previously reported. Properties of diagnostic tests may well vary between countries, laboratories and among populations of animals. In the absence of a true gold standard, the importance of validating new methods by appropriate statistical methods and with respect to the target population must be emphasized.
authors: Department of Clinical Sciences, Faculty of Veterinary Medicine and Animal Husbandry, Swedish University of Agricultural Sciences, 750 07 Uppsala, Sweden. Magdalena.Jacobson@kv.slu.se
authors: Magdalena
authors: M
authors: Jacobson
authors: Per
authors: P
authors: Wallgren
authors: Ann
authors: A
authors: Nordengrahn
authors: Malik
authors: M
authors: Merza
authors: Ulf
authors: U
authors: Emanuelson
mesh_terms: D000818:Animals; D000907:Antibodies, Bacterial / Q000097:blood*; D045824:Desulfovibrionaceae Infections / Q000175:diagnosis / Q000382:microbiology / Q000662:veterinary*; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods / Q000662:veterinary; D019084:Fluorescent Antibody Technique, Indirect / Q000379:methods / Q000662:veterinary; D020639:Lawsonia Bacteria / Q000276:immunology*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013552:Swine; D013553:Swine Diseases / Q000175:diagnosis / Q000382:microbiology*
chemical_list: D000907:Antibodies, Bacterial