Department of Epidemiology and Public Health, University of Maryland, 596 Howard Hall, 660 W. Redwood St., Baltimore, MD, 21201, USA,
Curr Top Microbiol Immunol. 2014;379:181-93. doi: 10.1007/82_2013_360.
Cholera is still a major public health problem. The underlying bacterial pathogen Vibrio cholerae (V. cholerae) is evolving and some of its mutations have set the stage for outbreaks. After V. cholerae acquired the mobile elements VSP I & II, the El Tor pandemic began and spread across the tropics. The replacement of the O1 serotype encoding genes with the O139 encoding genes triggered an outbreak that swept across the Indian subcontinent. The sxt element generated a third selective sweep and most recently a fourth sweep was associated with the exchange of the El Tor ctx allele for a classical ctx allele in the El Tor background. In Kenya, variants of this fourth selective sweep have differentiated and become endemic residing in and emerging from environmental reservoirs. On a local level, studies in Bangladesh have revealed that outbreaks may arise from a nonrandom subset of the genetic lineages in the environment and as the population of the pathogen expands, many novel mutations may be found increasing the amount of genetic variation, a phenomenon known as a founder flush. In Haiti, after the initial invasion and expansion of V. cholerae in 2010, a second outbreak occurred in the winter of 2011-2012 driven by natural selection of specific mutations.
霍乱仍然是一个主要的公共卫生问题。潜在的细菌病原体霍乱弧菌（V. cholerae）正在进化，其一些突变为暴发奠定了基础。在 V. cholerae 获得移动元件 VSP I 和 II 之后，埃尔托大流行开始并传播到热带地区。O1 血清型编码基因被 O139 编码基因取代，引发了一场席卷印度次大陆的疫情。sxt 元件引发了第三次选择清扫，最近第四次清扫与埃尔托 ctx 等位基因与埃尔托背景中的经典 ctx 等位基因的交换有关。在肯尼亚，这种第四次选择清扫的变体已经分化并成为地方性的，存在于环境储库中并从中出现。在当地，孟加拉国的研究表明，疫情可能是由环境中遗传谱系的非随机子集引起的，随着病原体种群的扩大，可能会发现许多新的突变，从而增加遗传变异量，这种现象称为奠基者效应。在海地，2010 年霍乱弧菌首次入侵和扩张后，2011-2012 年冬季发生了第二次疫情，这是由特定突变的自然选择驱动的。
