Marcotty T, Simukoko H, Berkvens D, Vercruysse J, Praet N, Van den Bossche P
Institute of Tropical Medicine Antwerp, Animal Health Department, Nationalestraat 155, B-2000 Antwerp, Belgium.
Prev Vet Med. 2008 Nov 17;87(3-4):288-300. doi: 10.1016/j.prevetmed.2008.05.002. Epub 2008 Jun 30.
In this study, packed cell volume-values (PCV) are evaluated as indicator of trypanosomiasis infections in cattle. A total of 734 blood samples were collected in 11 different sampling sites in eastern Zambia: 84 calves (< 1 year), 52 young females and 40 young males (between 1 and 3 years), 228 cows, 317 oxen and 13 bulls (> 3 years). All samples were subjected to three diagnostic tests: parasitological examination using the buffy coat method, PCR/RFLP and PCV determination. The results were compared and analysed in a Bayesian model, which allowed the estimation of the infection prevalence and the respective test sensitivities and specificities. The presence of a trypanosomal infection significantly reduced the PCV, independently of the age and sex of the infected animal. The estimated prevalence of trypanosomal infections in the study area was 34% (95% credibility interval: 30-38%). While the specificity of both the parasitological and the PCR/RFLP tests were set to 1, the parasitological diagnosis had a low sensitivity (37%) compared to the PCR/RFLP (96%). When using a cut-off value of 24, the PCV had a high specificity (98%) but a rather low sensitivity (53%) for identifying trypanosomiasis infections. Using 26% as a cut-off increased the sensitivity to 76% without much affecting the specificity (94%). A parallel combination of the parasitological diagnosis and the PCV improved the diagnostic sensitivity (74% and 89% for PCV cut-off values of 24% or 26%, respectively) while specificity remained high (98% and 94% for PCV cut-off values of 24% or 26%, respectively). These results suggest that such a combination could advantageously be used for the diagnosis of cattle trypanosomiasis in the field: it is much more sensitive than parasitological examination alone and it is much cheaper than molecular tests. However, the value of this approach depends largely on the determination of an appropriate cut-off value to consider a sample positive, depending on the required test sensitivities and specificities.
在本研究中，红细胞压积值（PCV）被评估为牛锥虫病感染的指标。在赞比亚东部的11个不同采样点共采集了734份血样：84头犊牛（<1岁）、52头青年母牛和40头青年公牛（1至3岁）、228头母牛、317头公牛和13头成年公牛（>3岁）。所有样本都接受了三项诊断测试：使用血沉棕黄层法进行寄生虫学检查、聚合酶链反应/限制性片段长度多态性分析（PCR/RFLP）以及PCV测定。对结果进行了比较，并在贝叶斯模型中进行分析，该模型可估算感染率以及各项测试的敏感性和特异性。锥虫感染的存在显著降低了PCV，这与感染动物的年龄和性别无关。研究区域内锥虫感染的估计患病率为34%（95%可信区间：30 - 38%）。虽然寄生虫学检查和PCR/RFLP测试的特异性均设定为1，但与PCR/RFLP（96%）相比，寄生虫学诊断的敏感性较低（37%）。当使用24作为临界值时，PCV对锥虫病感染的识别具有较高的特异性（98%），但敏感性较低（53%）。将临界值设定为26%可将敏感性提高到76%，而对特异性的影响不大（94%）。寄生虫学诊断和PCV的平行组合提高了诊断敏感性（PCV临界值为24%或26%时，敏感性分别为74%和89%），而特异性仍然很高（PCV临界值为24%或26%时，特异性分别为98%和94%）。这些结果表明，这种组合可有效地用于现场牛锥虫病的诊断：它比单独的寄生虫学检查更敏感，且比分子检测便宜得多。然而，这种方法的价值在很大程度上取决于根据所需的测试敏感性和特异性来确定一个合适的临界值以判定样本为阳性。
