Recent origins among ancient parasites.
Recent origins among ancient parasites.
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DOI：
10.1016/s0304-4017(03)00206-1
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发表时间：
2003
影响因子：
2.6
通讯作者：
L. David Sibley
中科院分区：
文献类型：
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作者：
L. David Sibley
弓形虫是一种分布广泛的原生动物寄生虫，隶属于尖端复合门。这组寄生虫的成员会在包括人类在内的各种动物中引起经济和医学上的重要疾病。弓形虫在这个群体中是值得注意的，因为它很容易感染几乎所有的温血脊椎动物，而大多数顶端复合体通常限制在它们的宿主范围内。弓形虫的各个菌株在基因上非常相似，分子研究表明绝大多数(>；95%)菌株可以归入三个不同的克隆谱系中的一个。值得注意的是，这三个谱系由两个亲本等位基因的不同组合组成，表明它们来自单一的遗传杂交。弓形虫不同寻常的种群结构起源于过去的10000年，而该属本身大约有1000万年的历史。这三个血统在最近起源后取得了显着的成功，这可能是由于生命周期发生了戏剧性的变化，极大地促进了传播。在产生克隆血统的杂交之前，在所有密切相关的寄生虫中，传播是通过在最终(食肉)和中间(食草)宿主之间交替的强制性双宿主生命周期进行的。发生在杂交中的基因的重新分类允许在许多不同的中间宿主之间直接口头传播。这些发现表明，复杂的生物生命周期可以迅速和戏剧性地变化，从而成为新的人畜共患病的持续来源。
Toxoplasma gondii is a wide spread protozoan parasite belonging to the phylum Apicomplexa. Members of this group of parasites cause economically and medically important diseases in a variety of animals, including humans. T. gondii is notable among this group for the fact that it readily infects virtually all warm-blooded vertebrates, while most apicomplexans are typically restricted in their host range. Individual strains of T. gondii are genetically quite similar and molecular studies indicate that the vast majority (>95%) of strains can be grouped into one of three distinct clonal lineages. Remarkably, these three lineages are comprised of different combinations of two parental alleles, indicating they arose from a single genetic cross. The unusual population structure of T. gondii originated within the last 10,000 years, while the genus itself is approximately 10 million years old. The remarkable success of the three lineages following their recent origin is likely attributable to a dramatic change in the life cycle that greatly facilitated transmission. Prior to the cross that gave rise to the clonal lineages, and in all closely related parasites, transmission occurred by an obligatory two-host life cycle that alternated between definitive (carnivorous) and intermediate (herbivorous) hosts. The reassortment of genes that occurred in the cross allowed direct oral transmission between many different intermediate hosts. These findings illustrate that complex biological life cycles can change rapidly and dramatically, thus presenting a constant source of new zoonotic infections.