Association between average daily gain, faecal dry matter content and concentration of Lawsonia intracellularis in faeces

<p>Abstract</p> <p>Background</p> <p>The objective of this study was to investigate the association between average daily gain and the number of <it>Lawsonia intracellularis</it> bacteria in faeces of growing pigs with different levels of diarrhoea.</p> <p>Methods</p> <p>A longitudinal field study (<it>n</it> = 150 pigs) was performed in a Danish herd from day 29 to 47 post weaning. Every third day all pigs were weighed, subjected to a clinical examination and faecal samples were obtained. Faecal samples were subjected to dry matter determination and absolute quantification by PCR for <it>L. intracellularis</it> and porcine circovirus type 2 (PCV2). Association between average daily gain, faecal dry matter content, numbers of <it>L. intracellularis</it> bacteria and PCV2 genome copies in faeces was investigated in a multilevel mixed-effects linear model.</p> <p>Results</p> <p>Increasing numbers of <it>L. intracellularis</it> log₁₀ bacteria/g faeces were significantly associated with decreasing average daily gain (<it>P</it> < 0.001). The association was decreasing with increasing faecal dry matter content (<it>P</it> < 0.01). The number of PCV2 log₁₀ copies/g faeces was not significantly associated with average daily gain of the pigs (<it>P</it> > 0.5).</p> <p>Conclusion</p> <p>The results suggest a potential application of a PCR quantifying <it>L. intracellularis</it> in growing pigs. Faecal dry matter content must be taken into consideration in interpretation of such test results.</p

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

<p>Abstract</p> <p>Background</p> <p><it>Lawsonia intracellularis </it>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 <it>L. intracellularis</it>-specific antibodies in sera. The aim of the present study was to evaluate a blocking ELISA in the detection of serum antibodies to <it>L. intracellularis</it>, by comparison to the previously widely used immunofluorescent antibody test (IFAT).</p> <p>Methods</p> <p>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.</p> <p>Results</p> <p>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%.</p> <p>Conclusion</p> <p>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.</p