March/April 2014 

Different strains of HIV

HIV can be divided into two main groups of viruses, as follows:

  • HIV-1
  • HIV-2

HIV-1 is the most common form of the virus and is found throughout the world. HIV-2 is most commonly found in West Africa but is being gradually displaced by HIV-1. This short report focuses on HIV-1 and its diversity.

HIV-1 can be subdivided into at least nine major strains, or subtypes, as follows:

  • A, B, C, D, F, G, H, J and K

All of these subtypes are classed as group M (or main) by virologists.

In North America, Western Europe, Australia and Japan, the most common subtype of HIV-1 is subtype B.

There are also six sub-subtypes of HIV-1, as follows:

  • A1 to A4, F1 to F2

There is another group of HIV called group O (outlier).

There are also many circulating recombinant forms (CRFs), at least 48 of them, such as the following:

  • AE, AB, BC

Due to travel, tourism and immigration, other strains and CRFs have been appearing in these countries and regions.

When a doctor submits a patient’s blood sample for genotypic resistance testing in Canada, the analysis that is sent from the lab to the doctor’s office lists the clade, or subtype, to which the patient’s virus belongs.

Subtypes of HIV may be an issue for the emerging class of therapies called attachment inhibitors, as we explain in the next report.

—Sean R. Hosein


  1. Lessells RJ, Katzenstein DK, de Oliveira T. Are subtype differences important in HIV drug resistance? Current Opinion in Virology. 2012 Oct;2(5):636-43.
  2. Siemieniuk RA, Beckthold B, Gill MJ. Increasing HIV subtype diversity and its clinical implications in a sentinel North American population. Canadian Journal of Infectious Diseases & Medical Microbiology. 2013 Summer;24(2):69-73.
  3. Ciccozzi M, Santoro MM, Giovanetti M, et al. HIV-1 non-B subtypes in Italy: a growing trend. New Microbiologica. 2012 Oct;35(4):377-86.