Two years ago, a new HIV strain was found in Russia, which caused the virus to spread at a rapid rate. The subtype was detected in the Siberian city of Novosibirsk in 2006. According to Forbes, it was responsible for over 50 percent of new HIV infections in the region in 2013.

After the new HIV strain was found in Russia, another much more aggressive and highly virulent HIV strain was recently discovered in patients in Cuba. As reported by RT.com, the new strain can progress to AIDS in just three years instead of the normal 5 to 10 years estimated window period.

Similar to the extremely virulent and new HIV strain discovered in Russia, the recently learned strain can developed into full-blown AIDS infection even before the patients realize they were infected. And while the Russian-discovered strain was just a single HIV subtype as The Huffington Post cited, the newly discovered strain is in fact a combination of three subtypes of the virus.

"Here we had a variant of HIV that we found only in the group that was progressing fast," lead study author, Professor Anne-Mieke Vandamme stated. "Not in the other two groups. We focused in on this variant [and] tried to find out what was different. And we saw it was a recombinant of three different subtypes."

The new study was published this week in the medical journal EBioMedicine, Press Herald revealed. And just like the new HIV in Russia, the recently discovered one also raises concerns among AIDS researchers. Experts are worried that mutated HIV viruses will be more difficult and challenging to diagnose. They also added that these new strains might become resistant to therapy and defy vaccine efforts.

The researchers studied the blood of 73 patients recently infected with HIV - 52 who had been diagnosed with AIDS, and 21 without AIDS. The patients with the aggressive strain had more virus in their blood as well as more of RANTES, a defensive molecules that the immune system develops in response to HIV. While recombinant virus strains originate when a person is infected by two different strains, whose DNA fuse to create a new form.

Aside from the new HIV strain found in Russia in 2013, an aggressive strain of HIV was discovered in Africa by researchers of Sweden's Lund University in November 2014. That virus strain was a fusion of the two most common HIV strains in Guinea-Bissau. It has so far only been found in West Africa.

The new HIV strain was found not in Russia this time but by researchers at Belgium-based KU Leuven's Laboratory for Clinical and Epidemiological Virology. The experts also express their concerns and fears that infected patients with the mutated virus may not seek antiretroviral therapy until it's too late.