Chanlun Aran, Emanuelson Ulf, Chanlun Suthida, Aiumlamai Suneerat, Björkman Camilla
Department of Clinical Sciences, Swedish University of Agricultural Sciences, Uppsala, Sweden.
Vet Parasitol. 2006 Mar 31;136(3-4):243-50. doi: 10.1016/j.vetpar.2005.11.025. Epub 2006 Jan 6.
In this prospective study, repeated bulk milk tests were evaluated to establish the Neospora caninum antibody status and to describe infection dynamics and changes in prevalence of N. caninum in Thai dairy herds. Bulk milk from 418 herds in northeast Thailand were collected at three consecutive samplings, in December 2002 (sampling 1), April (sampling 2) and December 2003 (sampling 3). All samples were analysed for presence of N. caninum antibodies by iscom ELISA, and the optical density values were dichotomized at three different cut-offs. Herd status at either sampling 1 or sampling 2 was used to predict herd status at sampling 3. Changes in both sensitivity and specificity at the first samplings at all cut-offs were consistent with commonly seen patterns when evaluating performance of diagnostic tests. In addition, the predictive positive values (PPV) of herd status at each of the two samplings were more affected by time of sampling than choice of cut-off, whereas the predictive negative values (PNV) increased with increasing cut-off. Herd status at the first samplings was also interpreted in combination, i.e. herds that were negative at both samplings were considered negative and positive otherwise in Combination A, while herds positive at both samplings were considered positive in Combination B. When using these combinations, Combination A gave higher PNV but lower PPV than Combination B at all cut-offs. Using the optical density value 0.20 as cut-off to establish the herd N. caninum antibody status, 270 herds (65%) kept their status throughout the study period, but 148 herds converted their status at least once. Interestingly, 136 (86%) of the 158 herds that were considered negative at sampling 1 and sampling 2 remained negative at sampling 3. In addition of the 159 herds considered positive at the first two samplings, 134 (84%) were still positive at sampling 3. We concluded that repeated bulk milk testing at regular intervals provided better information about herd N. caninum status than a single test. Further, our results showed that the infection is prevalent in northeast Thailand, but that a herd can keep a negative infection status despite the frequent presence of dogs.
在这项前瞻性研究中，对重复的散装牛奶检测进行评估，以确定犬新孢子虫抗体状态，并描述泰国奶牛群中犬新孢子虫的感染动态及流行率变化。2002年12月（采样1）、4月（采样2）和2003年12月（采样3）连续三次对泰国东北部418个牛群的散装牛奶进行采样。所有样本通过免疫刺激复合物酶联免疫吸附测定法（iscom ELISA）分析犬新孢子虫抗体的存在情况，光密度值在三个不同的临界值处进行二分法划分。使用采样1或采样2时的牛群状态来预测采样3时的牛群状态。在所有临界值下，第一次采样时敏感性和特异性的变化与评估诊断测试性能时常见的模式一致。此外，两次采样中每次采样时牛群状态的预测阳性值（PPV）受采样时间的影响大于临界值的选择，而预测阴性值（PNV）随着临界值的增加而增加。第一次采样时的牛群状态也进行了综合解读，即在组合A中，两次采样均为阴性的牛群被视为阴性，否则视为阳性；而在组合B中，两次采样均为阳性的牛群被视为阳性。使用这些组合时，在所有临界值下，组合A的PNV较高但PPV较低。以光密度值0.20作为临界值来确定牛群犬新孢子虫抗体状态，270个牛群（65%）在整个研究期间保持其状态，但148个牛群至少转换过一次状态。有趣的是，在采样1和采样2时被视为阴性的158个牛群中，有136个（86%）在采样3时仍为阴性。在前两次采样中被视为阳性的159个牛群中，有134个（84%）在采样3时仍为阳性。我们得出结论，定期重复进行散装牛奶检测比单次检测能提供关于牛群犬新孢子虫状态的更好信息。此外，我们的结果表明，该感染在泰国东北部很普遍，但尽管经常有狗存在，牛群仍可保持阴性感染状态。
