Pandemic HIV-1: Its Old Origin and Overlooked Mysteries

The oldest pandemic HIV-1 (group M) sequenceknown was, up to recently, the ZR59, isolated froman adult male from Kinshasa, Democratic Republicof Congo (DRC), in 1959 (Zhu, et al. Nature.1998;391:594-7). This sequence branches fromwithin the subtype D lineage after the latter splitsfrom B. The genetic distance between ZR59 and theM-root is about half of that of modern sequences.This fact alone suggested that the MRCA existeddecades prior to 1959, in line with molecular clockdating studies which placed it around 1920-1930(e.g. Salemi, et al. FASEB J. 2001;15:276-8; Korber,et al. Science. 2000;288:1789-96).