evidence: The human immunodeficiency virus (HIV) infects and destroys immune cells called CD4 cells in the body, causing the number of these cells to plummet. If left untreated, the infection then progresses to AIDS. In people infected with the newfound HIV variant, called the VB variant, the CD4 counts fall at about twice the rate as those of people infected with closely related HIV strains, meaning those of the same genetic subtype (B). [...] In other words, on top of being highly virulent, the VB variant may also be more transmissible than other versions of HIV. However, this finding is less conclusive than the evidence of increased virulence, since the tree provides only indirect evidence of the virus's transmissibility, Wymant said. [...] Future studies of the VB variant could reveal how it builds up in the blood and decimates CD4 cells so quickly, and also provide more details as to how the variant first evolved. The team found evidence that the variant steadily picked up its mutations, one by one, over time, but they couldn't tell if this evolution occurred in multiple individuals or just one, Wymant said.