MRC-University of Glasgow Centre for Virus Research, Glasgow, United Kingdom.
State Central Veterinary Laboratory, Transboundary Animal Disease Laboratory, Avian Influenza Section, Ulaanbaatar, Mongolia.
PLoS Pathog. 2019 Feb 7;15(2):e1007531. doi: 10.1371/journal.ppat.1007531. eCollection 2019 Feb.
Virus ecology and evolution play a central role in disease emergence. However, their relative roles will vary depending on the viruses and ecosystems involved. We combined field studies, phylogenetics and experimental infections to document with unprecedented detail the stages that precede initial outbreaks during viral emergence in nature. Using serological surveys we showed that in the absence of large-scale outbreaks, horses in Mongolia are routinely exposed to and infected by avian influenza viruses (AIVs) circulating among wild birds. Some of those AIVs are genetically related to an avian-origin virus that caused an epizootic in horses in 1989. Experimental infections showed that most AIVs replicate in the equine respiratory tract without causing lesions, explaining the absence of outbreaks of disease. Our results show that AIVs infect horses but do not spread, or they infect and spread but do not cause disease. Thus, the failure of AIVs to evolve greater transmissibility and to cause disease in horses is in this case the main barrier preventing disease emergence.
病毒生态学和进化在疾病出现中起着核心作用。然而，它们的相对作用将取决于所涉及的病毒和生态系统。我们结合了实地研究、系统发育学和实验感染，以前所未有的细节记录了病毒在自然界中出现时最初爆发之前的阶段。通过血清学调查，我们表明，在没有大规模爆发的情况下，蒙古的马匹经常接触并感染在野生鸟类中传播的禽流感病毒（AIV）。其中一些 AIV 与一种在 1989 年导致马群爆发的禽源病毒在基因上有关。实验感染表明，大多数 AIV 在马的呼吸道中复制而不引起病变，这解释了疾病爆发的缺失。我们的研究结果表明，AIV 感染马但不传播，或者感染并传播但不引起疾病。因此，在这种情况下，AIV 未能进化出更高的传染性并在马中引起疾病是阻止疾病出现的主要障碍。
