Implementation of an extended ZINB model in the study of low levels of natural gastrointestinal nematode infections in adult sheep.
Implementation of an extended ZINB model in the study of low levels of natural gastrointestinal nematode infections in adult sheep.
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DOI：
10.1186/s12917-016-0723-7
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发表时间：
2016-06-10
影响因子：
2.6
通讯作者：
Martínez-Valladares M
中科院分区：
文献类型：
--
作者：
Atlija M;Prada JM;Gutiérrez-Gil B;Rojo-Vázquez FA;Stear MJ;Arranz JJ;Martínez-Valladares M
本研究测定了529只成年绵羊对胃肠道线虫(GIN)抗性的两个相关性状：粪卵数(FEC)和血浆免疫球蛋白A活性(IgA)。在干旱年份，FEC在半扩展系统中可能非常低，例如这里研究的系统，这使得识别对感染具有抵抗力或易感的动物成为一项艰巨的任务。零膨胀负二项模型(ZINB)被用来计算FEC的零膨胀程度；该模型被扩展到包括来自IgA反应的信息。在这个数据集中，有30%的动物FEC为零，而ZINB模型表明38%的绵羊最近没有感染杜松子酒。因此，26%的绵羊被预测为卵数为零或低于检测下限的感染动物，很可能对线虫感染具有相对抵抗力。然后，所有动物的免疫球蛋白活性被用来确定哪些绵羊的蛋数为零，哪些绵羊最近没有暴露。零FEC和高IgA活性的动物被认为是抵抗的，而零FEC和低IgA活性的动物被认为不是最近感染的。对于被认为受到感染的动物，估计了所研究的性状之间的相关性，并评估了这些性状对未接触动物和感染动物的区分的影响。本文提出的模型改进了零FEC感染动物的检测。本文计算的相关性将有助于开发可靠的GIN抗性指数，这可能有助于在基于自然感染的研究中研究宿主抗性，特别是在成年绵羊中，也有助于设计旨在提高对寄生虫抗性的育种计划。本文的在线版本(doi：10.1186/s12917-0160723-7)包含补充材料，授权用户可以使用。
In this study, two traits related with resistance to gastrointestinal nematodes (GIN) were measured in 529 adult sheep: faecal egg count (FEC) and activity of immunoglobulin A in plasma (IgA). In dry years, FEC can be very low in semi-extensive systems, such as the one studied here, which makes identifying animals that are resistant or susceptible to infection a difficult task. A zero inflated negative binomial model (ZINB) model was used to calculate the extent of zero inflation for FEC; the model was extended to include information from the IgA responses. In this dataset, 64 % of animals had zero FEC while the ZINB model suggested that 38 % of sheep had not been recently infected with GIN. Therefore 26 % of sheep were predicted to be infected animals with egg counts that were zero or below the detection limit and likely to be relatively resistant to nematode infection. IgA activities of all animals were then used to decide which of the sheep with zero egg counts had been exposed and which sheep had not been recently exposed. Animals with zero FEC and high IgA activity were considered resistant while animals with zero FEC and low IgA activity were considered as not recently infected. For the animals considered as exposed to the infection, the correlations among the studied traits were estimated, and the influence of these traits on the discrimination between unexposed and infected animals was assessed. The model presented here improved the detection of infected animals with zero FEC. The correlations calculated here will be useful in the development of a reliable index of GIN resistance that could be of assistance for the study of host resistance in studies based on natural infection, especially in adult sheep, and also the design of breeding programs aimed at increasing resistance to parasites. The online version of this article (doi:10.1186/s12917-016-0723-7) contains supplementary material, which is available to authorized users.