日本血吸虫不同发育阶段的遗传变异：蜗牛中的分布和配对偏好是否有利于传播？
The genetic variation of different developmental stages of Schistosoma japonicum: do the distribution in snails and pairing preference benefit the transmission?
机构信息
Department of Parasitology, School of Basic Medical Sciences, Wuhan University, Wuhan, 430071, Hubei, China.
Hubei Provincial Center for Disease Control and Prevention, Wuhan, 430072, Hubei, China.
出版信息
Parasit Vectors. 2020 Jul 20;13(1):360. doi: 10.1186/s13071-020-04240-w.
BACKGROUND
Schistosoma japonicum is a waterborne parasite that causes schistosomiasis in humans and in more than 40 animal species. Schistosoma japonicum shows distinct genetic differentiation among geographical populations and multiple hosts, but the genetic diversity of different developmental stages of S. japonicum from is less studied. Such studies could elucidate ecological mechanisms in disease transmission by analysing feedbacks in individual physiology and population state.
METHODS
After infection using cercariae from a pool of snails shedding together (Method I) and infection using mixed equal numbers of cercariae from individually shed snails (Method II), different developmental stages of S. japonicum were genotyped with microsatellite loci, including 346 cercariae, 701 adult worms and 393 miracidia. Genetic diversity and molecular variation were calculated at different population levels. Kinships (I') among cercariae at intra-snail and inter-snail levels were evaluated. Genetic distance (Dsw) was compared between paired and unpaired worms, and partner changing was investigated through paternity identification for miracidia.
RESULTS
The cercaria clones in individual snails varied from 1 to 8 and the kinship of cercariae within individual snails was significant higher (P < 0.001) than that among different snails after deleting near-identical multi-locus genotypes (niMLGs). The allelic diversity of worms in Method I was lower (P < 0.001) than that in Method II, and allele frequency among mice in Method I was also less consistent. The parents of some miracidia were worms that were not paired when collected. The Dsw between each female of paired and unpaired males was much larger (P < 0.001) than that between the female and male in each pair.
CONCLUSIONS
Most of the infected snails contained multiple miracidia clones. The aggregation of genetically similar S. japonicum miracidia in individual snails and the unbalanced distribution of miracidia among snails suggests a non-uniform genetic distribution of cercariae among snails in the field. This further influenced the genetic structure of adult worms from infections with different cercariae sampling methods. Schistosoma japonicum in mice can change paired partner, preferring to mate with genetically similar worms. These characteristics provide implications for understanding the balance in genetic diversity of S. japonicum related to the transmission of schistosomiasis.
背景
日本血吸虫是一种水生寄生虫，可引起人类和 40 多种动物的血吸虫病。日本血吸虫在地理种群和多种宿主中表现出明显的遗传分化，但对其不同发育阶段的遗传多样性研究较少。通过分析个体生理和种群状态的反馈，此类研究可以阐明疾病传播中的生态机制。
方法
使用来自共同释放的蜗牛群的尾蚴进行感染（方法 I）和使用来自单独释放的蜗牛的等量混合尾蚴进行感染（方法 II）后，使用微卫星基因座对不同发育阶段的日本血吸虫进行基因分型，包括 346 条尾蚴、701 条成虫和 393 条尾蚴。在不同的种群水平上计算遗传多样性和分子变异。评估蜗牛内和蜗牛间尾蚴的亲缘关系（I'）。比较配对和未配对成虫之间的遗传距离（Dsw），并通过对尾蚴进行亲子鉴定来研究配偶更换。
结果
单个蜗牛中的尾蚴克隆数从 1 到 8 不等，在删除近等位基因多基因座基因型（niMLGs）后，同一蜗牛内尾蚴的亲缘关系显著高于不同蜗牛之间的亲缘关系（P<0.001）。方法 I 中蠕虫的等位基因多样性较低（P<0.001），并且方法 I 中老鼠之间的等位基因频率也不太一致。一些尾蚴的亲代在收集时没有配对。配对和未配对雄性之间的雌性之间的 Dsw 大得多（P<0.001），而每对中的雌性和雄性之间的 Dsw 则小得多。
结论
大多数受感染的蜗牛中含有多个尾蚴克隆。在单个蜗牛中，遗传上相似的日本血吸虫尾蚴聚集，以及蜗牛之间尾蚴分布不均，表明野外蜗牛中尾蚴的遗传分布不均匀。这进一步影响了不同尾蚴采样方法感染的成虫的遗传结构。日本血吸虫在小鼠中可以改变配对伴侣，更喜欢与遗传上相似的蠕虫交配。这些特征为了解与血吸虫病传播相关的日本血吸虫遗传多样性的平衡提供了启示。
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