Serological tests fail to discriminate dogs with visceral leishmaniasis that transmit Leishmania infantum to the vector Lutzomyia longipalpis

Abstract INTRODUCTION The control of reservoirs for Leishmania infantum -induced zoonotic visceral leishmaniasis requires the identification of dogs posing a population risk. Here, we assessed the performance of several assays to identify Lutzomyia longipalpis infectious dogs. METHODS We evaluated 99 dogs that were positive for visceral leishmaniasis based on parasite identification. Serological analyses were performed using an enzyme-linked immunosorbent assay, immunofluorescence antibody tests in 1:40 and 1:80 dilutions, rapid dual path platform tests, immunochromatographic assay with a recombinant rK39 antigen, fast agglutination screening tests, and direct agglutination tests. We also performed PCR to analyze peripheral blood and xenodiagnosis. RESULTS Forty-six dogs infected at least one L. longipalpis specimen. Although the serological test sensitivities were above 85% for detecting L. longipalpis infectious dogs, none showed a satisfactory performance, as both specificity (0.06 to 13%) and the area under the receiver operating characteristic curve (45 to 53%) were low. The PCR results were also weak, with a sensitivity of 30%, specificity of 72%, and an area under the receiver operating characteristic curve of 51%. The infected L. longipalpis proportion was higher among asymptomatic dogs than symptomatic dogs. Among the symptomatic dogs, those with ulceration-free skin diseases were more infectious, with an odds ratio of 9.3 (confidence interval of 1.10 - 428.5). The larger the number of insects fed, the greater the detected infectiousness. CONCLUSIONS Our study supports the imperative to develop novel technologies for identifying the infectious dogs that transmit L. infantum for the benefit of public health.

摘要 引言：针对婴儿利什曼原虫（Leishmania infantum）所致人畜共患内脏利什曼病的传染源防控，需明确具备种群传播风险的感染犬只。本研究评估了多种检测方法对长须罗蛉（Lutzomyia longipalpis）传播性感染犬的识别效能。

方法：本研究纳入99只经寄生虫鉴定确诊为内脏利什曼病阳性的犬只。采用以下方法开展血清学分析：酶联免疫吸附试验（enzyme-linked immunosorbent assay, ELISA）、1:40及1:80稀释度下的免疫荧光抗体试验、快速双通道平台试验、基于重组rK39抗原的免疫层析试验、快速凝集筛选试验及直接凝集试验。同时，通过聚合酶链式反应（PCR）分析外周血样本，并采用媒介接种诊断法（xenodiagnosis）进行检测。

结果：共有46只犬可使至少1只长须罗蛉获得感染。尽管各类血清学检测方法对长须罗蛉感染犬的灵敏度均高于85%，但均未表现出令人满意的检测效能：其特异度仅为0.06%~13%，受试者工作特征曲线（receiver operating characteristic curve, ROC曲线）下面积仅为45%~53%。PCR检测结果同样欠佳，灵敏度为30%，特异度为72%，ROC曲线下面积为51%。无症状犬的长须罗蛉感染率高于有症状犬。在有症状犬中，伴有无溃疡皮肤病变的犬只传染性更强，其比值比为9.3，置信区间为1.10~428.5。此外，媒介吸血数量越多，检测到的感染性越强。

结论：本研究证实，为保障公共卫生安全，亟需开发可识别传播婴儿利什曼原虫的感染犬的新型检测技术。