Bourdeau Patrick, Rowton Edgar, Petersen Christine
Laboratoire de Dermatologie, Parasitologie et Mycologie, ONIRIS, Ecole Nationale Veterinaire, Agroalimentaire et de l'Alimentation Nantes-Atlantique, Nantes, France; Immunology Program, Department of Internal Medicine and Microbiology, Carver College of Medicine, University of Iowa, Iowa City, IA 52242, USA.
Walter Reed Army Institute of Research, Silver Spring, MD, USA; Immunology Program, Department of Internal Medicine and Microbiology, Carver College of Medicine, University of Iowa, Iowa City, IA 52242, USA.
Vet Parasitol. 2020 Oct 10;287:109237. doi: 10.1016/j.vetpar.2020.109237.
Leishmania has biologically adapted to specific phlebotomine sand flies through long co-evolution. The ability of Leishmania spp. to bind to sand fly midgut allows each Leishmania species to propagate and differentiate into infectious promastigotes and be transmitted. Sand fly feeding upon a mammalian host is the first step towards being infected and a host of Leishmania. Once deposited into the skin, host susceptibility to infection vs. ability to mount a sterilizing immune response predicts which hosts could be reservoirs of different Leishmania spp. Materials, in addition to parasites, are expelled during sand fly during feeding, including salivary antigens and other factors that promote local inflammatory responses. These factors aid visceralization of infection increasing the likelihood that systemic infection is established. Any environmental factor that increases sand fly biting of a particular host increases that host's role in Leishmania transmission. First descriptions of reservoir species were based on association with local human disease and ability to observe infected leukocytes on cytology. This approach was one pathogen for one reservoir host. Advances in sensitive molecular tools greatly increased the breadth of mammals found to host Leishmania infection. Visceralizing species of Leishmania, particularly L. infantum, are now known to have multiple mammalian hosts. L. donovani, long been described as an anthroponotic parasite, was recently identified through molecular and serologic surveys to have additional mammalian hosts. The epidemiological role of these animals as a source of parasites to additional hosts via vector transmission is not known. Current evidence suggests that dogs and other domestic animals either control infection or do not have sufficient skin parasitemia to be a source of L. donovani to P. argentipes. Further xenodiagnosis and characterization of skin parasitemia in these different hosts is required to more broadly understand which Leishmania spp. hosts can be a source of parasites to sand flies and which ones are dead-end hosts.
利什曼原虫通过长期的共同进化在生物学上适应了特定的白蛉。利什曼原虫属与白蛉中肠结合的能力使每种利什曼原虫能够繁殖并分化为具有感染性的前鞭毛体，从而得以传播。白蛉吸食哺乳动物宿主是其被利什曼原虫感染并成为宿主的第一步。一旦利什曼原虫被注入皮肤，宿主对感染的易感性与产生杀菌性免疫反应的能力决定了哪些宿主可能成为不同利什曼原虫属的储存宿主。除了寄生虫外，白蛉在吸血时还会排出一些物质，包括唾液抗原和其他促进局部炎症反应的因素。这些因素有助于感染的内脏化，增加建立全身感染的可能性。任何增加白蛉叮咬特定宿主几率的环境因素都会增加该宿主在利什曼原虫传播中的作用。对储存宿主物种的最初描述是基于与当地人类疾病的关联以及在细胞学上观察感染白细胞的能力。这种方法是一种病原体对应一个储存宿主。敏感分子工具的进步极大地增加了被发现感染利什曼原虫的哺乳动物种类。现在已知内脏利什曼原虫，特别是婴儿利什曼原虫，有多种哺乳动物宿主。长期以来被描述为人畜共患寄生虫的杜氏利什曼原虫，最近通过分子和血清学调查发现还有其他哺乳动物宿主。这些动物作为寄生虫通过媒介传播给其他宿主的流行病学作用尚不清楚。目前的证据表明，狗和其他家畜要么控制感染，要么皮肤寄生虫血症不足以成为杜氏利什曼原虫传播给银足白蛉的来源。需要对这些不同宿主的皮肤寄生虫血症进行进一步的异种诊断和特征分析，以更广泛地了解哪些利什曼原虫属宿主可以成为白蛉的寄生虫来源，哪些是终末宿主。
