PNAS：利什曼原虫感染量小危害大

佚名

根据一个新的报告，被感染的白蛉的每一口叮咬都会传播数量不等的利什曼病致病原虫。反常的是，更低的感染剂量会导致宿主更严重的问题。David Sacks及其同事报告说，感染更高数量寄生虫的小鼠迅速出现了大的病灶，最终痊愈了。感染了更低剂量的小鼠出现了较小的病灶，但是常常出现慢性感染，让宿主成为了这种寄生虫的长期贮存宿主。利什曼病在许多热带和亚热带国家地方流行，而且常常导致被携带硕大利什曼原虫的白蛉叮咬的患者皮肤出现严重的疖。长期感染某些种类的利什曼原虫物种可能导致发热和贫血，并最终导致肝和脾的损伤。

研究人员研究了利什曼原虫从被感染的白蛉到小鼠的传播，发现了被传播寄生虫数量有很大的差异，但是可以归为两大类：3/4的小鼠从一口叮咬中接受了不到100个寄生虫，而其余的小鼠接受了多达10万个可能致病的细胞。这组作者提出，这种差异可能是该疾病结果的一个重要而被忽视的决定因素，而且它可能会帮助利什曼病疫苗的开发。相关论文发表在美国《国家科学院院刊》（PNAS）上。（生物谷Bioon.com）

生物谷推荐原始出处：

PNAS，doi：10.1073/pnas.0802331105，Nicola Kimblin，David Sacks

Quantification of the infectious dose of Leishmania major transmitted to the skin by single sand flies

Nicola Kimblin*, Nathan Peters*, Alain Debrabant^†, Nagila Secundino*, Jackson Egen^‡, Phillip Lawyer*, Michael P. Fay^§, Shaden Kamhawi*, and David Sacks*,^¶

Abstract

Leishmaniasis is transmitted between mammalian hosts by the bites of bloodsucking vector sand flies. The dose of parasites transmitted to the mammalian host has never been directly determined. We developed a real-time PCR-based method to determine the number of Leishmania major parasites inoculated into the ears of living mice during feeding by individual infected flies (Phlebotomus duboscqi). The number of parasites transmitted varied over a wide range in the 58 ears in which Leishmania were detected and demonstrated a clear bimodal distribution. Most of the infected mice were inoculated with a low dose of <600 parasites. One in four received a higher dose of >1,000 and up to 100,000 cells. High-dose transmission was associated with a heavy midgut infection of >30,000 parasites, incomplete blood feeding, and transmission of a high percentage of the parasite load in the fly. To test the impact of inoculum size on infection outcome, we compared representative high- (5,000) and low- (100) dose intradermal needle infections in the ears of C57BL/6 mice. To mimic natural transmission, we used sand fly-derived metacyclic forms of L. major and preexposed the injection site to the bites of uninfected flies. Large lesions developed rapidly in the ears of mice receiving the high-dose inoculum. The low dose resulted in only minor pathology but a higher parasite titer in the chronic phase, and it established the host as an efficient long-term reservoir of infection back to vector sand flies.