US researchers have announced their discovery of a new subtype of the human immunodeficiency virus that adds for the first time in 19 years a new entry into the catalogue of HIV viruses.

The researchers with Abbott, the drugs and devices giant, working with collaborators elsewhere, identified the new subtype after gene sequence studies on HIV extracted from three samples, two discovered in Congo in 1983 and 1990 and one collected in 2001.

The scientists have classified the new subtype as HIV-1 group M, subtype L, the first new subtype identified since guidelines for HIV nomenclature were established in 2000. They have published their findings in the Journal of Acquired Immune Deficiency Syndromes.

“Identifying new viruses such as this one is like searching for a needle in a haystack,” Mary Rodgers, head of the global viral surveillance programme at Abbott and the study’s co-author, said in a media release on Wednesday.

Rodgers and her colleagues used high-speed, low-cost genome sequence technology to analyse the preserved viral sequences.

While subtype L appears currently restricted to the Democratic Republic of Congo, the scientists said, continued molecular surveillance would be essential to determine its true prevalence and other rare or emerging strains of HIV.

Abbott scientists said the company’s core and molecular laboratory diagnostic tests can detect this new strain of HIV. The company said it would make available the new HIV strain to the research community to evaluate its impact on diagnostic testing, treatments and potential vaccines.

Two sequencing studies of HIV in India conducted between 2000 and 2007 had indicated that HIV-1 subtype C was the dominant virus, accounting for more than 95 per cent of HIV infections.

Since the discovery of HIV in 1983, over 75 million people have been infected with HIV and over 37 million persons are living with the virus today. When HIV multiplies in the human body, it cripples the immune system, leading to life-threatening opportunistic infections and cancers.

Anti-retroviral drugs can help keep viral loads low, rendering HIV a chronic infection, but do not cure HIV.

Research groups in several countries have been trying to develop vaccines against HIV, but most candidate vaccines have failed to provide substantial benefits in clinical trials. Other candidate vaccines are in trials under evaluation.