Babkin Igor V, Babkina Irina N
Laboratory of Molecular Microbiology, Institute of Chemical Biology and Fundamental Medicine, Novosibirsk 630090, Russia.
JSC VECTOR-BEST, Novosibirsk 630559, Russia.
Viruses. 2015 Mar 10;7(3):1100-12. doi: 10.3390/v7031100.
The question of the origin of smallpox, one of the major menaces to humankind, is a constant concern for the scientific community. Smallpox is caused by the agent referred to as the variola virus (VARV), which belongs to the genus Orthopoxvirus. In the last century, smallpox was declared eradicated from the human community; however, the mechanisms responsible for the emergence of new dangerous pathogens have yet to be unraveled. Evolutionary analyses of the molecular biological genomic data of various orthopoxviruses, involving a wide range of epidemiological and historical information about smallpox, have made it possible to date the emergence of VARV. Comparisons of the VARV genome to the genomes of the most closely related orthopoxviruses and the examination of the distribution their natural hosts' ranges suggest that VARV emerged 3000 to 4000 years ago in the east of the African continent. The VARV evolution rate has been estimated to be approximately 2 × 10-6 substitutions/site/year for the central conserved genomic region and 4 × 10-6 substitutions/site/year for the synonymous substitutions in the genome. Presumably, the introduction of camels to Africa and the concurrent changes to the climate were the particular factors that triggered the divergent evolution of a cowpox-like ancestral virus and thereby led to the emergence of VARV.
天花是人类面临的主要威胁之一，其起源问题一直是科学界关注的焦点。天花由被称为天花病毒（VARV）的病原体引起，该病毒属于正痘病毒属。在上个世纪，天花被宣布在人类社会中根除；然而，导致新的危险病原体出现的机制尚未完全明了。对各种正痘病毒的分子生物学基因组数据进行进化分析，并结合大量有关天花的流行病学和历史信息，使得确定天花病毒的出现时间成为可能。将天花病毒基因组与关系最为密切的正痘病毒基因组进行比较，并考察它们自然宿主范围的分布情况，结果表明天花病毒于3000至4000年前出现在非洲大陆东部。据估计，天花病毒基因组中央保守区域的进化速率约为2×10⁻⁶替换/位点/年，基因组中同义替换的进化速率为4×10⁻⁶替换/位点/年。据推测，骆驼被引入非洲以及同时发生的气候变化是引发类似牛痘的原始病毒发生分化进化从而导致天花病毒出现的特殊因素。
