Puzzling Origins of the Ebola Outbreak in the Democratic Republic of the Congo, 2014

Maganga et al. (1) and Naccache et al. (GenBank numbers KP271018, KP271019, and KP271020) recently reported the genome sequences of the Zaire Ebolavirus (ZEBOV) that caused the 2014 outbreak in the Democratic Republic of the Congo (COD). In contrast to the virus sampled from the ongoing outbreak in West Africa, the sequences from COD (COD/2014/Boende-Lokolia, COD/2014/Lomela-Lokolia16, COD/2014/Lomela-Lokolia17, and COD/2014/Lomela-Lokolia19) are phylogenetically close to the ZEBOVs isolated during the 1995-1996 outbreaks in equatorial Africa (Fig. 1A). Importantly, however, such sequence similarity is far greater than expected given the tree topology and higher rate of ZEBOV evolution determined previously (2, 3). In particular, regression analyses of root-to-tip genetic distances against time of sampling show that the COD sequences deviate from the generally clock-like evolution of other ZEBOVs (Fig. 1B to D). In particular, the COD viruses sampled in 2014 are no further distant from the root of the tree than those from 1994 to 1996, indicating that they have evolved at a lower rate than other ZEBOVs.