Feb 16, 2015 11:23 AM by NBC News
An aggressive strain of HIV found in Cuba can progress to full-blown AIDS within a few years if left untreated -- and now doctors think they're starting to understand why.
Researchers say it appears the virus mutated -- and is a combination of three subtypes of the virus.
Doctors say they worry infected patients may not seek treatment until it's too late. On average, it can take six to 10 years for untreated HIV-positive people to develop AIDS.
In the cases in Cuba -- doctors say the virus is progressing much faster, within about three years.
None of the patients studied in Cuba had received any treatment.