Davies C M, Webster J P, Woolhous M E
Wellcome Trust Centre for the Epidemiology of Infectious Disease, Department of Zoology, University of Oxford, UK.
Proc Biol Sci. 2001 Feb 7;268(1464):251-7. doi: 10.1098/rspb.2000.1367.
The adaptive trade-off theory for the evolution and maintenance of parasite virulence requires that virulence be genetically correlated with other fitness characteristics of the parasite. Many theoretical models rely on a positive correlation between virulence and transmissibility. They assume that high parasite replication rates are associated with a high probability of transmission (and, hence, increased parasite fitness), but also with high levels of damage to the host (high virulence). Schistosomes are macroparasites with an indirect life cycle involving a mammalian and a molluscan host. Here we demonstrate, through the development of five substrains, a genetic basis for schistosome virulence. We used these substrains further in order to investigate the presence of parasite fitness traits that were genetically correlated with virulence. High virulence in the (mouse) definitive host was, as predicted, positively correlated with parasite replication. In contrast, in the (snail) intermediate host high virulence was associated with low parasite replication rates. Variation in infectivity to and parasite replication in the definitive host was suggested as a compensating mechanism for the maintenance of virulence in the snail host. This is the first report of a trade-off in parasite reproductive success across hosts in an indirectly transmitted macroparasite.
寄生虫毒力进化与维持的适应性权衡理论认为，毒力与寄生虫的其他适合度特征存在遗传相关性。许多理论模型依赖于毒力与传播力之间的正相关关系。它们假定，寄生虫的高复制率与高传播概率（进而与寄生虫适合度增加）相关，但同时也与对宿主的高损伤水平（高毒力）相关。血吸虫是大型寄生虫，具有涉及哺乳动物和软体动物宿主的间接生命周期。在此，我们通过培育五个亚系，证明了血吸虫毒力的遗传基础。我们进一步利用这些亚系来研究与毒力存在遗传相关性的寄生虫适合度特征。正如所预测的，在（小鼠）终宿主中高毒力与寄生虫复制呈正相关。相反，在（蜗牛）中间宿主中，高毒力与低寄生虫复制率相关。终宿主中的感染性和寄生虫复制的变化被认为是蜗牛宿主中毒力维持的一种补偿机制。这是关于间接传播大型寄生虫在不同宿主间寄生虫繁殖成功存在权衡的首份报告。
