Abstract
BackgroundClassical faecal egg counts (FEC) provide less reliable diagnostic information for nematode infections in chickens. We developed an ELISA based on Ascaridia galli antigens and tested two hypotheses, as follows: (i) IgY antibodies developed against A. galli will also be useful to identify Heterakis gallinarum infections, and (ii) circulating antibodies stored in egg yolks are as good as plasma samples, so a non-invasive diagnosis is possible. The aim of this study, therefore, was to compare the diagnostic accuracy of the ELISA system with FEC, using both plasma and egg yolks from experimentally infected hens. In addition, naturally infected animals were evaluated to validate the assay.ResultsThe assay quantified large differences (P < 0.001) in plasma or in egg-yolk IgY concentrations between infected and uninfected animals in two experiments, each performed with either of the nematode species. The assay performed with high accuracy as quantified with the area under the ROC curve (AUC) values of > 0.90 for both nematodes using either plasma or egg yolks. Sensitivity of the assay was 94 and 93% with plasma and egg yolk samples, respectively, whereas FEC yielded in a sensitivity of 84% in A. galli experiment. Total test accuracy of the assay with plasma samples (AUC = 0.99) tended to be higher (P = 0.0630) than FEC (AUC = 0.92) for A. galli, while the assay with either sample matrix performed similar to FEC (AUC ≥ 0.91) for H. gallinarum. Among the three tests, the FECs correlated better with A. galli burden than the ELISA. Although 90% of naturally infected hens were correctly identified by the ELISA, 45% of the infected hens tested negative with FEC, indicating the validity of the higher test accuracy of the ELISA.ConclusionsAntigens of A. galli can be used successfully to identify H. gallinarum-infected animals, indicating that chickens develop cross-reactive antibodies against the two closely related species. Egg yolks are as informative as plasma samples, so that animal welfare-friendly sampling is possible. Although the assay with plasma samples reveals qualitative information of higher quality than FECs on the infection status of naturally infected birds, the latter is still a better tool to assess the intensity of A. galli but not of H. gallinarum infections.
Highlights
Classical faecal egg counts (FEC) provide less reliable diagnostic information for nematode infections in chickens
Direct effects result from the pathogenic consequences of infections, e.g. damage to the intestinal tissue [10] and resulting impairments in overall nutrient absorption, utilization and growth [11,12,13] as well as mortality, which may be caused by the obstruction of intestines in heavy infections with A. galli [14], recent evidence indicates an association between the presence of both nematode infections and hen mortality [15]
Average female worm length was 93 mm and the proportion of female worms to male worms was in describing infections of chickens with Ascaridia galli or Heterakis gallinarum
Summary
Classical faecal egg counts (FEC) provide less reliable diagnostic information for nematode infections in chickens. A few other nematode species, e.g. Syngamus trachea and Capillaria spp., and a few cestode species are encountered [2], the highest prevalence and worm burdens are from two phylogenetically closely related [6, 7] nematode species, A. galli and H. gallinarum. Both species are pathogenic to chickens [8, 9] and can impair overall productivity of hens through direct and indirect effects. Animal welfare, which was expected to improve with the EU legislative ban on battery cages [19], is threatened/endangered because of the overall effects of the infections on animal health and welfare [20]
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