Bertranpetit Emilie, Jombart Thibaut, Paradis Emmanuel, Pena Hilda, Dubey Jitender, Su Chunlei, Mercier Aurélien, Devillard Sébastien, Ajzenberg Daniel
INSERM UMR_S 1094, Neuroépidémiologie Tropicale, Laboratoire de Parasitologie-Mycologie, Faculté de Médecine, Université de Limoges, Limoges 87025, France.
MRC Centre for Outbreak Analysis and Modelling, Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, United Kingdom.
Infect Genet Evol. 2017 Mar;48:150-155. doi: 10.1016/j.meegid.2016.12.020. Epub 2016 Dec 24.
Toxoplasma gondii, a protozoan found ubiquitously in mammals and birds, is the etiologic agent of toxoplasmosis, a disease causing substantial public health burden worldwide, including about 200,000 new cases of congenital toxoplasmosis each year. Clinical severity has been shown to vary across geographical regions, with South America exhibiting the highest burden. Unfortunately, the drivers of these heterogeneities are still poorly understood, and the geographical origin and historical spread of the pathogen worldwide are currently uncertain. A worldwide sample of 168 T. gondii isolates gathered in 13 populations was sequenced for five fragments of genes (140 single nucleotide polymorphisms from 3153bp per isolate). Phylogeny based on Maximum likelihood methods with estimation of the time to the most recent common ancestor (TMRCA) and geostatistical analyses were performed for inferring the putative origin of T. gondii. We show that extant strains of the pathogen likely evolved from a South American ancestor, around 1.5 million years ago, and reconstruct the subsequent spread of the pathogen worldwide. This emergence is much more recent than the appearance of ancestral T. gondii, believed to have taken place about 11 My ago, and follows the arrival of felids in this part of the world. We posit that an ancestral lineage of T. gondii likely arrived in South America with felids and that the evolution of oral infectivity through carnivorism and the radiation of felids in this region enabled a new strain to outcompete the ancestral lineage and undergo a pandemic radiation.
刚地弓形虫是一种在哺乳动物和鸟类中普遍存在的原生动物，是弓形虫病的病原体，这种疾病在全球范围内造成了巨大的公共卫生负担，包括每年约20万例先天性弓形虫病新病例。临床严重程度在不同地理区域有所不同，南美洲的负担最重。不幸的是，这些异质性的驱动因素仍知之甚少，该病原体在全球的地理起源和历史传播目前尚不确定。对来自13个种群的168株刚地弓形虫分离株的全球样本进行了5个基因片段的测序（每个分离株从3153bp中获得140个单核苷酸多态性）。基于最大似然法并估计最近共同祖先时间（TMRCA）构建系统发育树，并进行地质统计学分析以推断刚地弓形虫的假定起源。我们发现，该病原体的现存菌株可能在约150万年前从南美洲的祖先进化而来，并重建了该病原体随后在全球的传播过程。这一出现时间比据信约在1100万年前出现的祖先刚地弓形虫要近得多，并且是在猫科动物抵达该地区之后。我们推测，刚地弓形虫的一个祖先谱系可能随猫科动物抵达南美洲，并且通过食肉习性产生的经口感染性的进化以及该地区猫科动物的辐射使得一个新菌株能够胜过祖先谱系并经历一次大流行辐射。
