The Rapid Test Based on <i>Leishmania infantum</i> Chimeric rK28 Protein Improves the Diagnosis of Canine Visceral Leishmaniasis by Reducing the Detection of False-Positive Dogs

Visceral Leishmaniasis (VL) has spread to many urban centers worldwide. Dogs are considered the main reservoir of VL, because canine cases often precede the occurrence of human cases. Detection and euthanasia of serologically positive dogs is one of the primary VL control measures utilized in some countries, including Brazil. Using accurate diagnostic tests can minimize one undesirable consequence of this measure, culling false-positive dogs, and reduce the maintenance of false-negative dogs in endemic areas. In December 2011, the Brazilian Ministry of Health replaced the ELISA (EIE CVL) screening method and Indirect Immunofluorescence Test (IFI CVL) confirmatory method with a new protocol using the rapid DPP CVL screening test and EIE CVL confirmatory test. A study of diagnostic accuracy of these two protocols was done by comparing their performance using serum samples collected from a random sample of 780 dogs in an endemic area of VL. All samples were evaluated by culture and real time PCR; 766 out of the 780 dogs were tested using the previous protocol (IFI CVL + EIE CVL) and all 780 were tested using the current protocol (DPP CVL + EIE CVL). Performances of both diagnostic protocols were evaluated using a latent class variable as the gold standard. The current protocol had a higher specificity (0.98 vs. 0.95) and PPV (0.83 vs. 0.70) than the previous protocol, although sensitivity of these two protocols was similar (0.73). When tested using sera from asymptomatic animals, the current protocol had a much higher PPV (0.63 vs. 0.40) than the previous protocol (although the sensitivity of either protocol was the same, 0.71). Considering a range of theoretical CVL prevalences, the projected PPVs were higher for the current protocol than for the previous protocol for each theoretical prevalence value. The findings presented herein show that the current protocol performed better than previous protocol primarily by reducing false-positive results.内脏利什曼病（Visceral Leishmaniasis, VL）已在全球众多城市中心蔓延。犬被视为VL的主要储存宿主，因为犬类感染病例通常早于人类病例出现。包括巴西在内的部分国家已将血清学阳性犬只的检测与安乐死，作为VL的核心防控措施之一。采用精准的诊断检测技术，可最大程度弱化该措施的不良影响：减少对假阳性犬只的淘汰，并降低流行区假阴性犬只的留存率。 2011年12月，巴西卫生部更新了VL检测方案，以新型快速DPP CVL筛查试验联合EIE CVL确证试验，替代原有的酶联免疫吸附试验（ELISA, EIE CVL）筛查法与间接免疫荧光试验（Indirect Immunofluorescence Test, IFI CVL）确证法。 本研究针对两种检测方案的诊断准确性开展对比评估，使用VL流行区780只犬的随机抽样血清样本进行性能测试。所有样本均通过培养法与实时PCR（real-time PCR）完成检测；其中766只犬采用原方案（IFI CVL + EIE CVL）完成检测，全部780只犬均采用现行方案（DPP CVL + EIE CVL）完成检测。两种检测方案的性能均以隐类别变量（latent class variable）作为金标准进行评价。 结果显示，相较于原方案，现行方案的特异度（0.98 vs 0.95）与阳性预测值（Positive Predictive Value, PPV, 0.83 vs 0.70）均更高，尽管二者的灵敏度（0.73）基本一致。在针对无症状动物血清的检测中，现行方案的PPV（0.63 vs 0.40）显著高于原方案，尽管二者的灵敏度均为0.71。在一系列理论CVL流行率场景下，现行方案的预估PPV在所有流行率取值下均高于原方案。 本研究结果表明，现行方案的性能优于原方案，核心优势在于有效减少了假阳性结果的产生。