HIV is a retrovirus

Retroviruses are unique in biology. Until their classification in the 1970s, it was believed that all organisms relied on the same fundamental system to turn their genetic code into the proteins necessary for life. The flow of genetic information was considered to be universally one way – code held in DNA was transcribed into RNA and then translated into proteins.

The recognition of retroviruses turned this view on its head. Retroviruses carry their genetic code as RNA, but instead of using the host’s cellular machinery to translate this RNA directly, as other RNA viruses do, they produce a unique enzyme, reverse transcriptase, which converts their RNA into DNA.

This DNA is then spliced into the host cell’s own genes, where it can settle down and wait for the activation of the host cell, when it will instruct it to make new virus particles.

Following HIV infection there will usually be a period of several years before any symptoms appear – diagnosis is made using a blood test to detect antibodies to the virus or copies of the virus itself. The length of this period varies from person to person, and depends on a wide range of factors, such as the amount of HIV present in the bloodstream, general health, the presence of other illnesses, and the response to treatment.

During this asymptomatic period, the virus is far from inactive. It is constantly replicating and causing damage to the immune system. The immune system is highly resilient, however, and it takes time for this damage to make an impact.