Types of HIV: 1 & 2

Instructor: Adrianne Baron

Adrianne has taught high school and college biology and has a master's degree in cancer biology.

In this lesson, we will aim to understand the two main types of HIV. Information on the groups and subtypes will be discussed and we will get a quick glimpse into how to the two types differ as well.


There have arguably never been three letters that can incite fear like the letters H-I-V. This is largely due to what those letters have come to mean to us within the last four decades. Prior to the '80s, those letters carried very little meaning and even less fear. HIV is the abbreviation for the term human immunodeficiency virus. A virus is a short piece or DNA or RNA. In the case of HIV, we are dealing with an RNA virus also referred to as a retrovirus.

HIV is a virus composed of RNA
Diagram of an HIV virion

HIV really began to hit the scene and make an impact in the '80s and rapidly became an epidemic that is still going. Very little was known about this virus early on. HIV causes an infection that attacks the immune system, rendering the body defenseless against invading bacteria, viruses and any other microorganisms.

Not all human immunodeficiency viruses are the same. There are different types as well as different subtypes. Some are more commonly associated with infection while others are rarely associated with infection.

HIV type 1

The first type of HIV and the one that most people are referring to when talking about HIV is HIV type 1. HIV-1 is the more prevalent and harmful of the two main types of HIV. It also contains the most number of subtypes which are organized into groups based on their prevalence. The three groups of HIV subtypes are M, N and O.

HIV type 1 Group M distribution
Map of HIV type 1 subtypes

The M group is for the major subtypes or the ones most commonly seen in the majority of HIV cases. The subtypes that are members of the M group include A, B, C, D, F, G, H, and K. Notice E and I are not included in the subtypes. This is the case because it was realized that the subtypes that were initially labeled as being E and I were actually a combination of two or more other subtypes. When the subtypes combine, we refer to this as circulating recombinant forms or CRF of HIV.

The N group isn't as well understood as the M group. You may hear this group referred to as the new group since it occurred more recently and doesn't fit into the other two main groups of HIV. There aren't any well-defined or classified subtypes in this group.

The other group under type 1 is the O group. In this case, the O stands for outliers. There are close to the same number of subtypes in the O group as we see in the M group, but they are extremely rare and that is why they are in the outlier group. The subtypes under the O group are also not clearly defined and understood.

HIV type 2

The second type of HIV is HIV type 2. The RNA sequence that makes up HIV-2 is completely different from the sequence in HIV-1. The differences in the sequences make HIV-2 naturally resistant to some anti-retroviral medications that are normally used to treat HIV-1. The groups that fall under the umbrella of HIV-2 are very distinct from each other as well. The groups are A, B, C, D, E, F and G. There are not any subtypes under the groups in HIV-2.

HIV type 2 is almost completely confined to West Africa
Map of West Africa

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