Investigation of canine visceral leishmaniasis in a non-endemic area in Brazil and the comparison of serological and molecular diagnostic tests

Abstract INTRODUCTION: Visceral leishmaniasis (VL) is an important zoonosis in Brazil. Previous identification of parasitized dogs can also help prevent the disease in humans, even in non-endemic areas of the country. The Brazilian Ministry of Health recommends diagnosis in dogs using a DPP® (rapid test) as a screening test and an immunoenzymatic assay (ELISA) as a confirmatory test (DPP®+ELISA), and culling infected dogs as a legal control measure. However, the accuracy of these serological tests has been questioned. METHODS: VL in dogs was investigated in a non-endemic area of the São Paulo state for three consecutive years, and the performances of different diagnostic tests were compared. RESULTS: A total of 331 dog samples were collected in 2015, 373 in 2016, and 347 in 2017. The seroprevalence by DPP®+ELISA was 3.3, 3.2, and 0.3%, respectively, and by indirect immunofluorescence assay (IFA), it was 3.0, 5.6, and 5.5%, respectively. ELISA confirmed 18.4% of DPP® positive samples. The concordance between the IFA and DPP® was 83.9%. The concordance between IFA and DPP®+ELISA was 92.9%. A molecular diagnostic test (PCR) was performed in 63.2% of the seropositive samples, all of which were negative. CONCLUSIONS: In non-endemic areas, diagnostic tests in dogs should be carefully evaluated to avoid false results.

摘要：
引言：内脏利什曼病（Visceral leishmaniasis, VL）是巴西境内的重要人畜共患病。此前研究表明，检出受利什曼原虫寄生感染的犬只，能够有效助力人类内脏利什曼病的防控，即便在巴西的非流行地区亦是如此。巴西卫生部推荐采用DPP®快速检测试剂盒作为犬只筛查手段，以酶联免疫吸附试验（ELISA）作为确证试验（即DPP®+ELISA联合检测方案），并将扑杀感染犬只作为法定防控措施。然而，上述血清学检测方法的准确性受到了学界质疑。

研究方法：本研究在圣保罗州的一处非流行地区，连续三年开展犬内脏利什曼病流行病学调查，并对比不同诊断检测方法的性能表现。

研究结果：2015年、2016年及2017年分别采集犬只血清样本331份、373份与347份。采用DPP®+ELISA联合检测得到的血清阳性率分别为3.3%、3.2%与0.3%；采用间接免疫荧光试验（IFA）得到的血清阳性率分别为3.0%、5.6%与5.5%。ELISA确证了18.4%的DPP®检测阳性样本。IFA与DPP®检测的一致性为83.9%，IFA与DPP®+ELISA联合检测的一致性为92.9%。本研究对63.2%的血清阳性样本开展了聚合酶链式反应（PCR）分子诊断检测，所有样本的检测结果均为阴性。

研究结论：在非流行地区，对犬只开展的内脏利什曼病诊断检测应当经过严格的性能评估，以避免出现假阳性或假阴性结果。