A Guide to the Different Types and Strains of HIV
There are also multiple groups and subtypes within each type of HIV. The various subtypes and strains differ in terms of how infectious they are and how they progress.
This article breaks it all down for you. It also reviews some basic statistics and issues relating to the differences between the types and strains of HIV, and it discusses treatment options.
HIV infection can occur from two genetically distinct viruses: HIV-1 and HIV-2. HIV-1 is the most prevalent form. It infects people all over the world, accounting for 95% of worldwide cases. It is also the predominant type in the United States. The latest data from the Centers for Disease Control and Prevention (CDC) show that more than 99.9% of U.S. HIV infections are from HIV-1.
HIV-2 is much less common than HIV-1. West Africa is the main area where HIV-2 infections occur. Scientists consider it endemic to this part of the world. This means it widely affects the population there. It can also affect countries with strong socioeconomic ties to West Africa, including:
- India (in some areas)
In the U.S., HIV-2 infections account for less than 0.03% of cases, according to the CDC.
The two virus types differ in how infectious they are and how they progress. HIV-2 is harder to transmit to another person and develops into AIDS more slowly. However, it will eventually become fatal without treatment. HIV-1 transmits easily and leads to AIDS more quickly.
There also appears to be a difference in the way the two types respond to treatment. There is less research into HIV-2. However, scientists know that non-nucleoside reverse transcriptase inhibitors (NNRTIs) will not work for it. Examples of this class of medications include nevirapine and efavirenz.
HIV tests will detect both kinds of viruses. The only screening antibody tests approved by the Food and Drug Administration to detect and differentiate HIV-2 infection from HIV-1 are the Geenius HIV 1/2 Supplemental Assay and the BioPlex 2200 HIV Ag-Ab Assay.
Within HIV-1, there are four distinct groups of viruses: M, N, O, and P. M stands for major. It is the main group responsible for infections worldwide. The other three groups are not very common. O causes about 5% of infections in some parts of Africa. N and P are rare. However, tests can detect all four groups of HIV-1.
Within the M group, there are nine distinct subtypes: A, B, C, D, F, G, H, J, and K. There are also circulating recombinant forms. These are hybrid viruses that form when subtypes combine. Nearly 90 of these hybrid viruses exist so far.
Group B is the main subtype that causes infections in the U.S. It also predominates in the rest of the Americas and Western Europe. Because of this, most research, including treatment studies, has focused on this subtype.
Group C is the main subtype in the rest of the world. It accounts for about 50% of worldwide infections.
With so much variation possible, it follows that the strain or subtype might matter in practical ways. Researchers have been studying this issue.
So far, it looks like there is not much difference as far as transmission or progression. Antiretroviral therapy (ART) seems to work well against the subtypes. However, subtype C may be less responsive to protease inhibitors (PIs).
Superinfection can also happen if someone contracts a drug-resistant form of the virus. This can make treatment more difficult. However, the CDC reports that hard-to-treat superinfections are rare occurrences.
If you have HIV, the best ways to prevent superinfection are to take your HIV medicines exactly as your doctor prescribed them and to use protection when engaging in sexual intercourse.
Treatment of HIV has made tremendous strides over the last few years. Treating the disease decreases the risk of transmission to others as well as progression to AIDS.
The goal of ART is to achieve undetectable viral load levels. In general, people should start ART as soon as possible after diagnosis.
HIV medications have different functions. Some prevent the virus from making copies of itself (replicating). Others work to protect the infection-fighting CD4 cells of the immune system. CD4 cells are the target of HIV. By blocking the virus from getting into these cells, some drugs deny HIV access to its target. This keeps the immune system strong, allowing it to fight infections.
ART involves a combination of drugs from the following classes:
- Chemokine coreceptor (CCR5) antagonists: These drugs block a receptor the virus needs to gain entry into CD4 cells.
- Fusion inhibitors: These drugs prevent the virus from fusing or merging with the CD4 cell membrane.
- Integrase strand transfer inhibitors (INSTIs): These drugs block an enzyme that the virus needs to insert its DNA into the CD4 cells’ DNA in order to replicate itself.
- Nucleoside reverse transcriptase inhibitors (NRTIs): These drugs insert themselves into the virus’s DNA when the virus is copying itself.
- NNRTIs: These drugs bind to an enzyme to make it useless to the virus.
- PIs: These drugs block a key enzyme the virus needs for replication.
- Post-attachment inhibitors: These block coreceptors on the CD4 cell.
The choice of classes and the drugs within each class will depend on your individual circumstances. You can get drug-resistance testing so your doctor knows whether there are any medicines that will not work against your strain of HIV.
HIV is actually a genetically diverse group of viruses instead of just one virus. It consists of two different types, which have groups and subtypes.
The dominant type in the United States is HIV-1. Of that type, the most common group is M and the main subtype is B. This strain of the virus responds well to ART. Hard-to-treat superinfections with a second strain of HIV are rare.
People should start treatment as soon as possible after diagnosis to decrease the risk of transmission to others and the progression to AIDS.