HIV-1 and HIV-2 are the two main types of HIV.
HIV-1 is the most common widespread type of virus worldwide while HIV-2, a less prevalent or in other words less infectious and less pathogenic (disease-causing) type as they progresses more slowly, is found principally in western Africa, Mozambique and Angola and rarely found elsewhere.
There are 2 major types of the human immunodeficiency virus namely HIV-1, which was discovered FIRST, is the most widespread type worldwide.
HIV-2 is more than 55% genetically different from HIV-1. Due to this genetic difference, HIV-1 and HIV-2 antigens are distinct enough that if a test is developed only to detect HIV-1, it will not reliably detect HIV-2.
However, tests which are sensitive to both types of virus have been developed. All the third-generation, fourth-generation and rapid tests which are listed in the following sections are sensitive to HIV-2 antibodies.
HIV-2 is most common in western Africa and is becoming more common in India, although numbers there are still relatively small. Small numbers of cases have also been seen in Portugal, France, other European countries including the UK and the Americas, largely in individuals of west African origin or their sexual partners.
Should a laboratory not usually use a test which is sensitive to HIV-2, but the person testing has lived in a country where HIV-2 is common (or has a sexual partner from one of those countries), it is important to use a different test for this person. Moreover, if a person has clinical signs of HIV infection (e.g. recurrent opportunistic infections) but does not test positive to a test which is sensitive only to HIV-1, then testing specifically for HIV-2 would be appropriate.
Each major type of virus can be further broken down into groups, which themselves can be subdivided into clades or subtypes. HIV-1 comprises groups M (main), O (outlier), and N (non-M or O). Screening tests in developed countries were originally developed to identify the most common HIV subtype in those regions – group M, clade B. In addition, third- and fourth-generation ELISA antibody tests are reliably able to detect group O virus, and the full range of group M subtypes.