Viral Special Pathogens Branch, Division of High Consequence Pathogens and Pathology, Centers for Disease Control and Prevention, 1600 Clifton Road, Atlanta, Georgia 30333, USA.
J Virol. 2011 Jul;85(13):6162-7. doi: 10.1128/JVI.00335-11. Epub 2011 Apr 20.
Rift Valley fever virus (RVFV), a mosquito-borne phlebovirus, has been detected in Madagascar since 1979, with occasional outbreaks. In 2008 to 2009, a large RVFV outbreak was detected in Malagasy livestock and humans during two successive rainy seasons. To determine whether cases were due to enzootic maintenance of the virus within Madagascar or to importation from the East African mainland, nine RVFV whole genomic sequences were generated for viruses from the 1991 and 2008 Malagasy outbreaks. Bayesian coalescent analyses of available whole S, M, and L segment sequences were used to estimate the time to the most recent common ancestor for the RVFVs. The 1979 Madagascar isolate shared a common ancestor with strains on the mainland around 1972. The 1991 Madagascar isolates were in a clade distinct from that of the 1979 isolate and shared a common ancestor around 1987. Finally, the 2008 Madagascar viruses were embedded within a large clade of RVFVs from the 2006-2007 outbreak in East Africa and shared a common ancestor around 2003 to 2004. These results suggest that the most recent Madagascar outbreak was caused by a virus likely arriving in the country some time between 2003 and 2008 and that this outbreak may be an extension of the 2006-2007 East African outbreak. Clustering of the Malagasy sequences into subclades indicates that the viruses have continued to evolve during their short-term circulation within the country. These data are consistent with the notion that RVFV outbreaks in Madagascar result not from emergence from enzootic cycles within the country but from recurrent virus introductions from the East African mainland.
裂谷热病毒（RVFV）是一种蚊媒沙粒病毒，自 1979 年以来一直在马达加斯加被检测到，偶尔会爆发。2008 年至 2009 年，在两个连续的雨季，马达加斯加的牲畜和人类中爆发了大规模的 RVFV。为了确定病例是否是由于病毒在马达加斯加境内的地方性维持，还是由于从东非大陆输入，对来自 1991 年和 2008 年马达加斯加疫情的九种 RVFV 全基因组序列进行了生成。对现有全 S、M 和 L 节段序列进行贝叶斯合并分析，以估计 RVFV 最近共同祖先的时间。1979 年马达加斯加分离株与大陆上的菌株在 1972 年左右有共同的祖先。1991 年马达加斯加分离株与 1979 年分离株不同，有共同的祖先大约在 1987 年。最后，2008 年马达加斯加病毒嵌入了来自 2006-2007 年东非爆发的一个大裂谷热病毒分支，并在 2003 年至 2004 年左右有一个共同的祖先。这些结果表明，最近马达加斯加的疫情是由一种可能在 2003 年至 2008 年期间进入该国的病毒引起的，而这次疫情可能是 2006-2007 年东非疫情的延续。马达加斯加序列聚类成亚分支表明，这些病毒在该国的短期循环过程中继续进化。这些数据与裂谷热病毒在马达加斯加的爆发不是由于该国境内的地方性循环产生，而是由于从东非大陆反复引入病毒的观点是一致的。
