International Centre of Insect Physiology and Ecology (icipe), P.O. Box 30772-00100, Nairobi, Kenya.
Kenya Medical Research Institute, Off Mbagathi Road, P.O. Box 54840-00200, Nairobi, Kenya.
Parasit Vectors. 2021 Jan 18;14(1):53. doi: 10.1186/s13071-020-04517-0.
Visceral leishmaniasis (VL) and zoonotic cutaneous leishmaniasis (ZCL) are of public health concern in Merti sub-County, Kenya, but epidemiological data on transmission, vector abundance, distribution, and reservoir hosts remain limited. To better understand the disease and inform control measures to reduce transmission, we investigated the abundance and distribution of sand fly species responsible for Leishmania transmission in the sub-County and their blood-meal hosts.
We conducted an entomological survey in five villages with reported cases of VL in Merti sub-County, Kenya, using CDC miniature light traps and castor oil sticky papers. Sand flies were dissected and identified to the species level using standard taxonomic keys and PCR analysis of the cytochrome c oxidase subunit 1 (cox1) gene. Leishmania parasites were detected and identified by PCR and sequencing of internal transcribed spacer 1 (ITS1) genes. Blood-meal sources of engorged females were identified by high-resolution melting analysis of vertebrate cytochrome b (cyt-b) gene PCR products.
We sampled 526 sand flies consisting of 8 species, Phlebotomus orientalis (1.52%; n = 8), and 7 Sergentomyia spp. Sergentomyia squamipleuris was the most abundant sand fly species (78.71%; n = 414) followed by Sergentomyia clydei (10.46%; n = 55). Leishmania major, Leishmania donovani, and Trypanosoma DNA were detected in S. squamipleuris specimens. Humans were the main sources of sand fly blood meals. However, we also detected mixed blood meals; one S. squamipleuris specimen had fed on both human and mouse (Mus musculus) blood, while two Ph. orientalis specimens fed on human, hyrax (Procavia capensis), and mouse (Mus musculus) blood.
Our findings implicate the potential involvement of S. squamipleuris in the transmission of Leishmania and question the dogma that human leishmaniases in the Old World are exclusively transmitted by sand flies of the Phlebotomus genus. The presence of Trypanosoma spp. may indicate mechanical transmission, whose efficiency should be investigated. Host preference analysis revealed the possibility of zoonotic transmission of leishmaniasis and other pathogens in the sub-County. Leishmania major and L. donovani are known to cause ZCL and VL, respectively. However, the reservoir status of the parasites is not uniform. Further studies are needed to determine the reservoir hosts of Leishmania spp. in the area.
内脏利什曼病（VL）和动物源性皮肤利什曼病（ZCL）是肯尼亚 Merti 县的公共卫生关注问题，但有关传播、媒介丰度、分布和储存宿主的流行病学数据仍然有限。为了更好地了解疾病并为减少传播的控制措施提供信息，我们调查了该县负责利什曼原虫传播的沙蝇物种的丰度和分布及其血源宿主。
我们在肯尼亚 Merti 县报告有 VL 病例的五个村庄进行了一项昆虫学调查，使用 CDC 微型灯诱捕器和蓖麻油粘性纸。通过标准分类学关键和细胞色素 c 氧化酶亚基 1（cox1）基因的 PCR 分析对沙蝇进行解剖和鉴定到种水平。通过 PCR 和内部转录间隔区 1（ITS1）基因测序检测和鉴定利什曼原虫寄生虫。通过高分辨率熔解分析脊椎动物细胞色素 b（cyt-b）基因 PCR 产物鉴定饱血雌性的血源。
我们共采集了 526 只沙蝇，包括 8 个物种，东方伊蚊（1.52%；n=8）和 7 种塞氏疟蚊属。塞氏疟蚊属中塞氏疟蚊属（78.71%；n=414）最为丰富，其次是塞氏疟蚊属（10.46%；n=55）。在塞氏疟蚊属标本中检测到利什曼原虫、利什曼原虫和锥虫 DNA。人类是沙蝇血液的主要来源。然而，我们还检测到混合的血液来源；一只塞氏疟蚊属标本既吸食了人类和老鼠（Mus musculus）的血液，而两只东方伊蚊吸食了人类、蹄兔（Procavia capensis）和老鼠（Mus musculus）的血液。
我们的研究结果表明，塞氏疟蚊属可能参与了利什曼原虫的传播，并质疑旧世界人类利什曼病仅由伊蚊属沙蝇传播的教条。锥虫属的存在可能表明存在机械传播，其效率应进行调查。宿主偏好分析显示，该地区可能存在利什曼病和其他病原体的动物源性传播。已知利什曼原虫和利什曼原虫分别引起 ZCL 和 VL。然而，寄生虫的储存宿主并不统一。需要进一步研究来确定该地区利什曼原虫属的储存宿主。
