HIV-1 and HIV-2

  • HIV-1 and HIV-2 are the two main types of HIV.
  • HIV-1 is the most widespread type worldwide. HIV-2, a less prevalent and less pathogenic (disease-causing) type, is found principally in western Africa.
  • Large genetic differences between HIV-1 and HIV-2 mean that tests keyed to one will not reliably detect the other.

There are two major types of the human immunodeficiency virus. 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. Moreover, the Health Protection Agency recommends that such a test should be used.1 2

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.

In this book, mention of 'HIV' refers to HIV-1 unless otherwise stated.

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.

There are two main HIV-2 subtypes, A and B. Issues to do with the transmission of HIV-2 and different HIV-1 subtypes are covered in previous sections.

Related Links

References

  1. Parry JV et al. Towards error-free HIV diagnosis: guidelines on laboratory practice. Comm Dis Pub Health 6:334-350, 2003
  2. Dougan S et al. Diagnoses of HIV-1 and HIV-2 in England, Wales and Northern Ireland associated with west Africa. Sexually Transmitted Infections 81:338-341, 2005
This content was checked for accuracy at the time it was written. It may have been superseded by more recent developments. NAM recommends checking whether this is the most current information when making decisions that may affect your health.