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.

引言：内脏利什曼病（Visceral leishmaniasis, VL）是巴西境内一种重要的人畜共患病。即便在巴西的非流行地区，提前筛查出感染寄生虫的犬只，也有助于预防人类感染该疾病。巴西卫生部推荐对犬只采用DPP®快速检测试剂进行筛查，以酶联免疫吸附试验（ELISA）作为确认试验（即DPP®+ELISA联合检测方案），并将感染犬只扑杀作为法定防控措施。不过，上述血清学检测方法的准确性受到了质疑。
方法：本研究在圣保罗州的一处非流行地区，针对犬内脏利什曼病开展了连续三年的调查，并对比了不同诊断检测方法的性能。
结果：2015年、2016年、2017年分别采集犬样本331份、373份、347份。经DPP®+ELISA联合检测的血清阳性率分别为3.3%、3.2%和0.3%；经间接免疫荧光试验（IFA）检测的血清阳性率则分别为3.0%、5.6%和5.5%。18.4%的DPP®检测阳性样本经ELISA确认属实。IFA与DPP®检测结果的符合率为83.9%，IFA与DPP®+ELISA联合检测的结果符合率为92.9%。本研究对63.2%的血清阳性样本实施了聚合酶链式反应（PCR）分子诊断检测，结果全部呈阴性。
结论：在非流行地区，需对犬只的诊断检测方案进行审慎评估，以规避检测结果失真的问题。