Coffey Lark L, Vasilakis Nikos, Brault Aaron C, Powers Ann M, Tripet Frédéric, Weaver Scott C
Department of Pathology and Center for Tropical Diseases, University of Texas Medical Branch, Galveston, TX 77555, USA.
Proc Natl Acad Sci U S A. 2008 May 13;105(19):6970-5. doi: 10.1073/pnas.0712130105. Epub 2008 May 5.
The intrinsic plasticity of RNA viruses can facilitate host range changes that lead to epidemics. However, evolutionary processes promoting cross-species transfers are poorly defined, especially for arthropod-borne viruses (arboviruses). In theory, cross species transfers by arboviruses may be constrained by their alternating infection of disparate hosts, where optimal replication in one host involves a fitness tradeoff for the other. Accordingly, freeing arboviruses from alternate replication via specialization in a single host should accelerate adaptation. This hypothesis has been tested by using cell culture model systems with inconclusive results. Therefore, we tested it using an in vivo system with Venezuelan equine encephalitis virus (VEEV), an emerging alphavirus of the Americas. VEEV serially passaged in mosquitoes exhibited increased mosquito infectivity and vertebrate-specialized strains produced higher viremias. Conversely, alternately passaged VEEV experienced no detectable fitness gains in either host. These results suggest that arbovirus adaptation and evolution is limited by obligate host alternation and predict that arboviral emergence via host range changes may be less frequent than that of single host animal RNA viruses.
RNA病毒的内在可塑性可促进宿主范围变化，进而引发疫情。然而，促进跨物种传播的进化过程却鲜为人知，尤其是对于虫媒病毒而言。理论上，虫媒病毒的跨物种传播可能受到其在不同宿主间交替感染的限制，即在一个宿主中实现最佳复制可能会在另一个宿主中付出适应性代价。因此，通过在单一宿主中实现专业化，使虫媒病毒摆脱交替复制，应该会加速其适应性进化。这一假设已通过细胞培养模型系统进行了测试，但结果尚无定论。因此，我们使用委内瑞拉马脑炎病毒（VEEV）这一美洲新兴的甲病毒，通过体内系统对其进行了测试。在蚊子中连续传代的VEEV表现出更高的蚊子感染性，而脊椎动物特异性毒株则产生了更高的病毒血症。相反，交替传代的VEEV在任何一个宿主中均未表现出可检测到的适应性增强。这些结果表明，虫媒病毒的适应性进化受到宿主交替的限制，并预测通过宿主范围变化而出现的虫媒病毒可能比单宿主动物RNA病毒更为罕见。
