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Visceral leishmaniasis (VL), also known as kala-azar, is caused by Leishmania spp. and transmitted by sandflies of the genus Phlebotomus (1). Most cases die from complications within 1–2 years without timely diagnosis and treatment. Globally, VL is the second deadliest parasitic disease. About 50,000 to 90,000 new cases were reported annually globally (2), mainly those living in poverty.
There are three types of VL in China, namely anthroponotic visceral leishmaniasis (AVL), mountain-type zoonotic visceral leishmaniasis (MT-ZVL), and desert-type zoonotic visceral leishmaniasis (DT-ZVL). Their epidemiological characteristics are significantly divergent (3). VL was rampant in more than 600 counties north of the Yangtze River in the early 1950s, and an estimated 530,000 VL cases were distributed in China in 1951 (4). The disease was controlled in most endemic areas through active control by 1960 and elimination standards were achieved in the early 1980s (4). However, VL rebounded from the late 1980s and an outbreak was observed in Jiashi County of Xinjiang Uyghur Autonomous Region in 2015 (5), with a record high of 353 cases reported that accounted for 70.9% of the total cases in China at that time. Although a great deal of human and material resources have been devoted to controlling VL, no comprehensive epidemiological analysis of VL based on the three endemic types has been reported since 2015. The objective of this study was to characterize the epidemiological status and trends of VL from 2015 to 2019 to provide evidence-based data to support the adjustment of appropriate strategies and measures in the future.
Data were collected via the National Notifiable Disease Reporting System (NNDRS) between 2015 and 2019. The indigenous and imported cases were defined according to epidemiological investigations on individual cases conducted by county-level CDCs. The spatiotemporal and demographic distribution of cases was analyzed through descriptive statistics with Microsoft Excel (version 2016, Microsoft, USA).
During 2015–2019, a total of 1,360 VL cases were reported from 216 counties in 17 provincial-level administrative divisions (PLADs). The number of VL cases decreased from 2015 (n=498) to 2019 (n=166). Among them, 1,188 (87.4%) cases were indigenous cases in 77 endemic counties and the other 172 (12.6%) cases were imported to 139 non-endemic counties. The number and proportion of indigenous cases decreased from 2015 (n=480, 96.4%) to 2019 (n=125, 75.3%), while the number and proportion of imported cases increased from 2015 (n=18, 3.6%) to 2019 (n=41, 24.7%). The indigenous cases consisted of 70 (5.9%) AVL, 589 (49.6%) DT-ZVL, and 529 (44.5%) MT-ZVL cases (Table 1). The proportion of DT-ZVL cases decreased from 2015 (n=385, 77.3%) to 2019 (n=3, 1.8%), while the number and proportion of MT-ZVL cases increased from 2015 (n=82, 16.5%) to 2019 (n=122, 73.5%).
Year Endemic areas Imported cases in non-endemic areas (n, %) Total(n) AVL(n, %) DT-ZVL(n, %) MT-ZVL(n, %) Subtotal(n, %) 2015 13(2.6) 385(77.3) 82(16.5) 480(96.4) 18(8.6) 498 2016 22(6.8) 178(55.3) 95(29.5) 295(91.6) 27(3.4) 322 2017 24(12.4) 17(8.8) 113(58.2) 154(79.4) 40(20.6) 194 2018 11(6.1) 6(3.3) 117(65.0) 134(74.4) 46(25.6) 180 2019 0(0.0) 3(1.8) 122(73.5) 125(75.3) 41(24.7) 166 Total 70(5.1) 589(43.3) 529(38.9) 1188(87.4) 172(12.6) 1360 Abbreviations: AVL=anthroponotic visceral leishmaniasis; MT-ZVL=mountain-type zoonotic visceral leishmaniasis; DT-ZVL=desert-type zoonotic visceral leishmaniasis. Table 1. Number and proportion of visceral leishmaniasis cases in China (2015–2019).
VL cases were mainly distributed in Xinjiang (n=673, 49.5%), Gansu (n=314, 23.1%), and Shanxi (n=126, 9.3%). A total of 1,188 (87.4%) indigenous cases were reported in 77 endemic counties in Xinjiang (30 counties), Gansu (16 counties), Shanxi (13 counties), Shaanxi (9 counties), Sichuan (6 counties), Henan (2 counties), and Hebei (1 county) (Table 2). Among them, Jiashi County (498 cases) in Xinjiang and Zhouqu County (110 cases), Wudu District (80 cases), and Dangchang County (55 cases) in Gansu Province were major VL endemic counties that reported more than 10 cases annually, which accounted for 54.6% (743/1,360) of total cases in the period. Jiashi County recorded the highest annual incidence (2.4/10,000), followed by Zhouqu County (1.6/10,000), and all other counties recorded less than 1.0/10,000.
Types PLADs (No. of cases) CLADs (No. of cases) AVL Xinjiang(70) Kashgar (17), Shache (17), Kuqa (9), Yingjisha (7), Atush (5), Shule (5), Akto (3), Shufu (3), Shaya (2), Aksu (1), Wushi (1), DT-ZVL Xinjiang(589) Jiashi (498), Bachu (39), Yuepuhu (11), Minfeng (8), Zepu (6), Yuli (4), Jiashi farm (4), Korla (3), Qiemo (3), Tumshuk (3), Gaochang (2), Awati (1), Celle (1), Luntai (1), Toksun (1), 44th regiment farm (1), 46th regiment farm (1), 50th regiment farm (1), 53rd regiment farm (1) MT-ZVL Gansu(291) Zhouqu (110), Wudu (80), Dangchang (55), Wenxian (15), Diebu (12), Huanxian (3), Qingshui (3), Xihe (3), Lixian (2), Maiji (2), Gangu (1), Qinzhou (1), Qingcheng (1), Wushan (1), Zhenyuan (1), Tongwei (1) Shanxi(115) Suburb of Yangquan (31), Pingding (21),Urban of Yangquan (15), Wuxiang (12), Mining of Yangquan (7), Xiangning (6), Xiangfen (6), Luzhou (5), Quwo (4), Daning (3), Hejin (2), Xiangyuan (2), Yuxian (1) Shaanxi(66) Hancheng (35), Linwei (8), Huazhou (6), Qingjian (4), Yichuan (4), Baota (4), Suide (2), Yanchang (2), Ningqiang (1) Sichuan(47) Jiuzhaigou (19), Heishui (13), Lixian (6), Maoxian (4), Wenchuan (4), Pingwu (1) Henan(8) Linzhou (7), Long'an (1) Hebei(2) Xingtai (2) Abbreviations: CLADs=county-level administrative divisions; PLADs=provincial-level administrative divisions; AVL=anthroponotic visceral leishmaniasis; MT-ZVL=mountain-type zoonotic visceral leishmaniasis; DT-ZVL=desert-type zoonotic visceral leishmaniasis. Table 2. Distribution and endemic types of visceral leishmaniasis cases in county-level administrative divisions (CLADs) in China (2015–2019).
In this period, VL reemerged in 13 historically-endemic counties: Wushan and Zhenyuan in Gansu Province; Xiangning, Quwo, Xiangfen, and Hejin in Shanxi Province; Suide, Yanchang, Huazhou, and Linwei in Shaanxi Province; Linzhou and Long'an in Henan Province; and Xingtai in Hebei Province. There were 48 indigenous cases in total.
Approximately 56.4% (n=767) cases belonged to the age group of 0–2 years. In endemic areas, the age characteristics varied in different types of VL cases. For AVL and DT-ZVL, 42.9% and 95.1% cases were in the age group of 0–2 years with a median age of 3.7 and 0.9 years, respectively. For MT-ZVL, 51.6% cases in the age group ≥15 years with a median age of 19.5 years. In addition, the majority of imported cases (86.0%) were in group ≥15 years with a median age of 41.8 years (Table 3).
Characters Endemic area Imported cases in non-endemic area (n, %) Total (n, %) AVL (n, %) DT-ZVL (n, %) MT-ZVL (n, %) Subtotal (n, %) Age group/year 0–2 30 (42.9) 560 (95.1) 164 (31.0) 754 (63.5) 13 (7.6) 767 (56.4) 3–6 10 (14.3) 14 (2.4) 47 (8.9) 71(6.0) 4 (2.3) 75 (5.5) 7–14 9 (12.9) 3 (0.5) 45 (8.5) 57 (4.8) 7 (4.1) 64 (4.7) ≥15 21 (30.0) 12 (2.0) 273 (51.6) 306 (25.8) 148 (86.0) 454 (33.4) Occupation Infants and young children 42 (60.0) 574 (97.5) 215 (40.6) 831 (70.0) 17 (9.9) 848 (62.4) Students 7 (10.0) 3 (0.5) 53 (10.0) 63 (5.3) 7 (4.1) 70 (5.1) Farmers 11 (15.7) 9 (1.5) 187 (35.4) 207 (17.4) 96 (55.8) 303 (22.3) Workers 1 (1.4) 0 (0.0) 9 (1.7) 10 (0.8) 14 (8.1) 24 (1.7) Officials 1 (1.4) 0 (0.0) 11 (2.1) 12 (1.0) 3 (1.7) 15 (1.1) Housewives 7 (10.0) 1 (0.2) 27 (5.1) 35 (3.0) 14 (8.1) 49 (3.6) Others 1 (1.4) 2 (0.3) 27 (5.1) 30 (2.5) 21 (12.2) 51 (3.8) Gender Male 38 (54.3) 338 (57.4) 327 (61.8) 703 (59.2) 119 (69.2) 822 (60.4) Female 32 (45.7) 251 (42.6) 202 (38.2) 485 (40.8) 53 (30.8) 538 (39.6) Total (n) 70 589 529 1,188 172 1,360 Table 3. Demographics of visceral leishmaniasis cases in China (2015–2019).
Infants and young children were the high risk population of VL, accounting for 62.4% (848/1,360) of the total cases, which was followed by farmers 22.3% (303/1,360). The majority cases (70.0%) in endemic areas were infants and young children, followed by farmers (17.4%). However, the occupational distribution varied in different types of VL cases. For AVL, the predominant cases (60.0%) were infants and young children followed by farmers (15.7%). For DT-ZVL, most of cases were infants and young children (97.5%). For MT-ZVL, the majority of cases were infants and young children (40.6%) followed by farmers (35.4%). in non-endemic areas, the majority (55.8%) cases were farmers (Table 3). In addition, the gender distribution showed that most cases (n=822, 60.4%) were male, and 538 cases (39.6%) were female.
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