Scientists have found an aggressive strain of human immunodeficiency virus (HIV) in Cuba that they say can progress to AIDS so rapidly that patients may not even know they are infected before symptoms appear, Medical News Today reported.

The Cuban variant of HIV is categorized as a recombinant version of the virus, which can occur if a person engages in unprotected sex with multiple infected partners and contracts multiple strains of the HIV virus, which later recombine within a person to create a new variant.

In a normal HIV infection, the virus attaches to proteins on the membranes of cells known as CCR5 before it is able to penetrate the cell. The HIV-infected patient may experience a number of healthy years before the virus becomes CXCR4, which quickly progresses to AIDS, according to the report.

In the new Cuban strain, researchers found that HIV makes the transition to CXCR4 more quickly than in the other strains, resulting in a shorter number of “healthy” years. The new strain can cause AIDS to appear within just three years of infection, Medical News Today reported.

To analyze this strain, researchers compared recently-infected patients with the recombinant form of HIV to patients who had progressed to AIDS after the normal period of infection, and found the recombinant HIV patients had abnormally high doses of the virus as well as high numbers of defensive molecules called RANTES, Medical News Today reported.

The presence of RANTES was significant because as part of the typical human response to the virus it binds to CCR5, indicating that the recombinant HIV would have to bypass CCR5 because the protein wasn’t available for the virus to anchor to it as it normally would. When the recombinant virus bypasses the CCR5 and becomes CXCR4, it eliminates the “healthy” stage, Medical News Today reported.

“So this group of patients that progressed very fast, they were all recently infected,” Anne-Mieke Vandamme, study author and medical professor at Belguim’s University of Leuven, told Voice of America. “And we know that because they had been HIV-negative tested one or a maximum two years before.”

Also aiding in the transition to CXCR4, researchers noted, was the presence of a protease, which is an enzyme that cuts proteins in new viruses to enable it to replicate in greater numbers.

Researchers are calling for people who have unprotected sex with multiple partners to be tested early, and often, so that treatment can begin.

The teams’ findings were published in the journal EBioMedicine.

Click for more from Medical News Today.