Evaluation of a blocking ELISA for the detection of antibodies against Lawsonia intracellularis in pig sera

Abstract

BackgroundLawsonia 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).MethodsSera 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.ResultsAt 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%.ConclusionThe 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.

Evaluation and use of a serological assay for the detection of antibodies toLawsonia intracellularisin swine

“…The commercial ELISA has a manufacturer claimed sensitivity and specificity of 96.5 and 98.7% [16]. However, the current study found that the sensitivity was slightly lower at 91% and the specificity was higher at 100% with experimentally derived samples of known status and higher than the values reported by Jacobson et al's comparison to the IFAT [17].…”

“…As the immunofluorescence antibody test (IFAT) is comparatively less specific and prone to false positive results and less commonly available, this method was not included for assessment in this study. Moreover, the performance of the commercial ELISA has been compared to the IleiTest IFAT (Elanco Animal Health, Indianapolis, Indiana, USA) [17]. In this study, when compared to the IFAT, the sensitivity of the blocking ELISA was 72%, specificity was 93%, the positive predictive value was 0.82 and the negative predictive value was 0.89.…”

“…The manufacturer-claimed performance metrics for this assay included a sensitivity of 96.5% and specificity of 98.7%. However, only one report comparing the performance of the commercial ELISA to the IFAT, which is not widely available, is published so far [17]. Therefore, in this study we have evaluated the performance of the commercial ELISA by comparing its performance with assays such as the IPMA and LPS ELISA.…”

Factors associated with the growing-finishing performances of swine herds: an exploratory study on serological and herd level indicators

“…Serum samples from all pigs were tested for antibodies against L. intracellularis (SVANOVIR L.intracellularis/Ileitis-Ab, Boehringer Ingelheim Svanova, Sweden, successor of the bioScreen Ileitis Antibody ELISA with sensitivity (Se) ranging from 72 to 96.5% and specificity (Sp) from 83 to 100%; [ 17 – 19 ]), M. hyopneumoniae ( Mycoplasma hyopneumoniae ELISA, OXOID Ltd., UK; formely DAKO ELISA; with Sp = 100% and Se ranging from 49% to 100% according to experimental trials [ 20 – 23 ]) and PCV2 (SERELISA® PCV2 Ab Mono Blocking, Synbiotics Europe, France, Se = 86% and Sp = 85% [ 24 ]). A serum sample was considered positive for L. intracellularis antibodies if the percentage inhibition was ≥30% [ 18 ].…”

Advances in Ileitis Control, Diagnosis, Epidemiology and the Economic Impacts of Disease in Commercial Pig Herds

“…Serology can help producers and veterinarians identify risk factors and the efficacy and optimal timing for PE control measures including vaccination, medication and improved hygiene [37][38][39]. The sensitivity of this blocking ELISA was between 72% and 90.5% and the specificity was between 83% and 93%, using sera from both field and experimental challenge trials [40,41]. Regardless of which serological assay is used, L. intracellularis antibodies are not routinely detected until about 21 days post challenge, after clinical signs and fecal shedding are already observed, so serology is an indicator of previous infection [42,43].…”