Center for Infectious Diseases, Parasitology, Heidelberg University Hospital, Heidelberg, Germany.
Mali International Center of Excellence in Research, University of Sciences, Techniques and Technologies of Bamako, Bamako, Mali.
Nat Med. 2020 Dec;26(12):1929-1940. doi: 10.1038/s41591-020-1084-0. Epub 2020 Oct 26.
The dry season is a major challenge for Plasmodium falciparum parasites in many malaria endemic regions, where water availability limits mosquito vectors to only part of the year. How P. falciparum bridges two transmission seasons months apart, without being cleared by the human host or compromising host survival, is poorly understood. Here we show that low levels of P. falciparum parasites persist in the blood of asymptomatic Malian individuals during the 5- to 6-month dry season, rarely causing symptoms and minimally affecting the host immune response. Parasites isolated during the dry season are transcriptionally distinct from those of individuals with febrile malaria in the transmission season, coinciding with longer circulation within each replicative cycle of parasitized erythrocytes without adhering to the vascular endothelium. Low parasite levels during the dry season are not due to impaired replication but rather to increased splenic clearance of longer-circulating infected erythrocytes, which likely maintain parasitemias below clinical and immunological radar. We propose that P. falciparum virulence in areas of seasonal malaria transmission is regulated so that the parasite decreases its endothelial binding capacity, allowing increased splenic clearance and enabling several months of subclinical parasite persistence.
在许多疟疾流行地区,旱季是恶性疟原虫寄生虫的主要挑战,在这些地区,水的供应使蚊子媒介一年中只能存在一部分时间。恶性疟原虫如何在相隔数月的两个传播季节之间架起桥梁,而不会被宿主清除或危及宿主的生存,这一点我们还不太了解。在这里,我们表明,在长达 5-6 个月的旱季期间,无症状的马里个体血液中仍存在低水平的恶性疟原虫寄生虫,很少引起症状,也很少影响宿主的免疫反应。在旱季分离出的寄生虫与传播季节发热性疟疾个体中的寄生虫在转录上是不同的,这与寄生红细胞在每个复制周期内的循环时间更长而不附着在内皮细胞上相一致。旱季期间寄生虫水平较低并不是由于复制受损,而是由于脾脏清除循环时间更长的感染红细胞的能力增强,这可能使寄生虫血症保持在临床和免疫雷达以下。我们提出,季节性疟疾传播地区恶性疟原虫的毒力受到调节,使寄生虫降低其内皮结合能力,从而增加脾脏清除能力,并使数月的亚临床寄生虫持续存在成为可能。