Human Immunodeficiency Virus (HIV) is an RNA virus which converts RNA to DNA, which makes it a retrovirus. Retroviruses use single stranded RNA as a template to make double stranded DNA using a viral enzyme. A person who becomes infected with HIV results in a complex clinical disease known as acquired immune deficiency syndrome(AIDS), which may take ten years or more to develop.



HIV contains a protein that is called “reverse transcriptase" which is crucial for viral replication inside of T-cells. This eventually causes the immune system to shut down causing an extremely low tolerance to infectious diseases and eventually death.

HIV is passed on when the virus from an infected person gets into the blood stream of someone else, this can occur during unprotected sex between same sex and or heterosexual couples, there is a small chance of infection through unprotected oral sex, although the exact size of this risk is unclear. There is no method of barrier protection that completely eliminates the risk; however the use of condoms is considered the safest form of protection.

HIV can also be passed on when people use dirty needles for injections or tattoos; this can be avoided by using single use or sterilized needles. People who inject drugs can avoid infection by never sharing injection needles; it can also be transmitted, in rare cases, through being stuck with a needle that has been used by an infected person. Additionally, a baby can contract the disease by being born to an infected mother or by breastfeeding from an infected woman.

Because the early symptoms of HIV are not always obvious, a person may be able to pass on the virus before they realize that they are infected. HIV cannot be passed on through normal day to day contact, such as sitting on toilet seats or by shaking hands.

Like all viruses, HIV is comprised of only genetic material, a few proteins and a protective envelope, its genetic material, carried by single stranded RNA molecules, contains all the information needed to make more viruses. HIV can not reproduce itself outside of a cell, but when HIV invades a living cell, it turns the cell into a factory for making more HIV.

The development of HIV occurs when the virus infects CD4 T-lymphocytes; a type of white blood cell, HIV weakens the immune system and leaves the infected individual open to deadly infections. The viruses gain access to a T-lymphocyte by attaching to CD4 proteins on the outer surface of the cell membrane. HIV infects certain human cells by binding its envelope glycoprotein’s gp120 and gp41 to specific molecules on the surface of the cells. Only cells which carry the appropriate molecules are susceptible to infection by HIV.

In the 1980s, scientists quickly recognised that a molecule called CD4, which is found particularly on certain T-lymphocytes (a type of white blood cell), was the primary binding site, but it was only in 1996 that other co-receptors that are also required for infection were identified. Fusion of the virus with the cell membrane permits the viral nucleotide to enter the cell.

As HIV disease progresses, HIV variants called synctium-inducing (SI) strains evolve within the individual’s body. SI variants can use an additional co-receptor on human cells, called CXCR4. This may allow HIV to infect a wider range of cells. Once fusion has taken place, reverse transcription then occurs to convert the viral genomic RNA into double-stranded DNA. The viral DNA is transported to the cell nucleus and is integrated, or inserted, into the normal cellular chromosomal DNA.

When the right activation signals are present, the process of making new virions begins. Using the replication machinery of the host cell, the integrated viral DNA is transcribed to make messenger RNA (mRNA) and new strands of viral genomic RNA. The viral mRNA is then translated into a protein string that is cleaved into specific viral proteins.

Assembly of new virions then takes place within the cell, and the new HIV particles are released by budding from the cell surface, taking a piece of the cell membrane as their envelope.

HIV replication can directly kill CD4 + T-lymphocytes. The loss of these cells paralyses the immune system and is one mechanism by which HIV infection causes AIDS.

People who have HIV may look and feel completely well, but their immune systems may nevertheless be damaged. There are no set symptoms for HIV or AIDS, usually if a person becomes infected with HIV they do not notice they have been infected, some may however suffer from a flu like illness shortly after infection. It is important to note that once someone is infected they can pass HIV on, even if they feel well.

The more time passes, the more likely damage is to have occurred to the immune system. Once the immune system is compromised, the person may be susceptible to ‘opportunistic infections’, these are infections that are around us all the time and can normally be fought off by a healthy immune system. Also, some tumours or cancers can occur as a result of a damaged immune system and can cause damage to the brain and nervous system. These ‘symptoms’ are not caused by HIV, but by the opportunistic infections, so until the immune system is so damaged that other infections begin to cause health problems which become increasingly difficult to treat.

The only way to know if a person is infected is for them to have and HIV Antibody Test. HIV and AIDS is such a world wide epidemic it is vitally important that people are educated in the disease.

Zidovudine (brand name retrovir), formerly known as AZT from its synthetic chemical name, azidothymidine, is the drug most commonly used in the treatment of HIV infection. The drug inhibits the replication of HIV by interfering with the process of reverse transcription, which is necessary for the production of new virus particles.

Zidovudine was shown by clinical trials in 1986 to be effective at improving survival in patients with AIDS, and has since then been licensed as the first choice treatment for HIV infection in Europe, North America and Australia. The drug appears temporarily to delay the progression of disease and death in people who have HIV infection symptoms, but does not significantly delay the development of AIDS in HIV-positive people without symptoms.

Zidovudine is increasingly prescribed as part of a combination of antiviral drugs, and a recent international study conducted in Britain and the United States showed that this approach results in greatly enhanced survival when compared with Zidovudine treatment alone.

It appears to have a significant protective effect against HIV related brain disease and dementia. This is due to the ease with which the drug crosses the blood brain barrier, a quality not shared by other anti HIV drugs that have come into use subsequently. Because of the lack of effective treatment for HIV, more importance is put on preventive strategies. All blood donors are screened for HIV, greatly reducing any chances of contracting HIV through a blood transfusion, or through factor VIII for haemophiliacs.

A key preventive strategy has been to change behaviour through education and promotion of safe sex. This has been promoted through advertising and education, with television taking the lead in promoting the use of condoms, especially to young people.

The transmission of HIV through intravenous drug users is also reduced by education, and there is also a Government sponsored needle exchange programme, where clean needles can be collected free of charge, thus stopping the infection being passed on by the sharing of dirty needles.