School of Biological Sciences, Washington State University, Pullman, WA, United States.
School of Biological Sciences, Washington State University, Pullman, WA, United States.
Adv Virus Res. 2018;101:129-148. doi: 10.1016/bs.aivir.2018.02.005. Epub 2018 Apr 26.
Viruses persist outside their hosts in a variety of forms, from naked virions to virus protected in sloughed tissues or carcasses, and for a range of times, all of which affect the likelihood and importance of transmission from the environment. This review synthesizes the literature on environmental persistence of viruses in the genus Ranavirus (family Iridoviridae), which are large double-stranded DNA viruses of ectothermic, often aquatic or semiaquatic vertebrates. Ranaviruses have been associated with mass mortality events in natural and captive settings around the world, and with population and community-wide declines in Europe. Early work suggested ranaviruses are environmentally robust and transmission from the environment should be common. More recent work has shown a large effect of temperature and microbial action on persistence times, although other aspects of the environment (e.g., water chemistry) and aquatic communities (e.g., zooplankton) may also be important. Ranaviruses may persist in the carcasses of animals that have died of infection, and so decomposing organisms and invertebrate scavengers may reduce these persistence times. The question is, do persistence times vary enough to promote or preclude substantial transmission from the environment. We built an epidemiological model with transmission from contacts, free virus in water, and carcasses, to explore the conditions in which environmental persistence could be important for ranavirus epidemiology. Based on prior work, we expected a substantial amount of transmission from the water and that longer persistence times would make this route of transmission dominant. However, neither water-borne nor transmission from carcasses played an important role in the simulated epidemics except under fairly restrictive conditions, such as when there were high rates of virus shedding or high rates of scavenging on highly infectious carcasses. While many aspects of environmental persistence of ranaviruses are being resolved by experiments, key parameters such as viral shedding rates are virtually unknown and will need to be empirically constrained if we are to determine whether environmental persistence and transmission from the environment are essential or insignificant features of Ranavirus epidemiology. We conclude by emphasizing the need to place environmental persistence research in an epidemiological framework.
病毒在其宿主外以多种形式存在，从裸露的病毒粒子到包裹在脱落组织或尸体中的病毒，存在时间长短不一，所有这些都影响着病毒从环境中传播的可能性和重要性。本综述综合了有关虹彩病毒属（虹彩病毒科）病毒在环境中持久性的文献，该属病毒是大型双链 DNA 病毒，宿主为变温动物，通常为水生或半水生脊椎动物。虹彩病毒与世界各地自然和圈养环境中的大规模死亡事件以及欧洲的种群和群落范围的下降有关。早期的研究表明，虹彩病毒具有很强的环境适应性，因此从环境中的传播应该很常见。最近的研究表明，温度和微生物作用对持久性时间有很大影响，尽管环境的其他方面（例如，水化学）和水生群落（例如，浮游动物）也可能很重要。虹彩病毒可能会在感染后死亡的动物尸体中存活，因此，分解有机物和无脊椎动物清道夫可能会缩短这些存活时间。问题是，存活时间是否足够长以促进或阻止从环境中进行大量传播。我们建立了一个传染病模型，该模型的传播途径包括接触、水中的游离病毒和尸体，以探讨环境持久性对虹彩病毒流行病学的重要性。根据先前的研究，我们预计从水中会有大量的传播，而且较长的持久性时间将使这种传播途径成为主要途径。然而，在模拟的疫情中，无论是通过水传播还是通过尸体传播都没有发挥重要作用，除非在相当严格的条件下，例如当病毒脱落率很高或高度感染性尸体上的清道夫数量很高时。虽然实验正在解决虹彩病毒环境持久性的许多方面，但关键参数（例如病毒脱落率）实际上是未知的，如果我们要确定环境持久性和从环境中传播是否是虹彩病毒流行病学的重要特征，那么需要进行经验性限制。我们最后强调需要将环境持久性研究置于流行病学框架内。
