>HIV(Human immuno deficiency virus)

Introduction of HIV

HIV and Immune cells

HIV stands for: Human Immunodeficiency Virus

HIV is a virus. Viruses such as HIV cannot grow or reproduce on their own, they need to infect the cells of a living organism in order to replicate (make new copies of themselves). The human immune system usually finds and kills viruses fairly quickly, but HIV attacks the immune system itself – the very thing that would normally get rid of a virus.

With around 2.7 million people becoming infected with HIV in 2008, there are now an estimated 33 million people around the world who are living with HIV, including millions who have developed AIDS.

The Structure of HIV:

In this computer generated image, the large object is a human CD4+ white blood cell, and the spots on its surface and the spiky blue objects in the foreground represent HIV particles. 

HIV virus structure

Outside of a human cell, HIV exists as roughly spherical particles (sometimes called virions). The surface of each particle is studded with lots of little spikes.
An HIV particle is around 100-150 billionths of a metre in diameter. That's about the same as:

• 0.1 microns
• 4 millionths of an inch
• one twentieth of the length of an E. coli bacterium
• one seventieth of the diameter of a human CD4+ white blood cell.

Unlike most bacteria, HIV particles are much too small to be seen through an ordinary microscope. However they can be seen clearly with an electron microscope.

HIV particles surround themselves with a coat of fatty material known as the viral envelope (or membrane). Projecting from this are around 72 little spikes, which are formed from the proteins gp120 and gp41. Just below the viral envelope is a layer called the matrix, which is made from the protein p17.

The proteins gp120 and gp41 together make up the spikes that project from HIV particles, while p17 forms the matrix and p24 forms the core.

The viral core (or capsid) is usually bullet-shaped and is made from the protein p24. Inside the core are three enzymes required for HIV replication called reverse transcriptase, integrase and protease. Also held within the core is HIV's genetic material, which consists of two identical strands of RNA.

Viral class of HIV:

HIV belongs to a special class of viruses called retroviruses. Within this class, HIV is placed in the subgroup of lentiviruses. Other lentiviruses include SIV, FIV, Visna and CAEV, which cause diseases in monkeys, cats, sheep and goats. Almost all organisms, including most viruses, store their genetic material on long strands of DNA. Retroviruses are the exception because their genes are composed of RNA (Ribonucleic Acid).

RNA has a very similar structure to DNA. However, small differences between the two molecules mean that HIV's replication process is a bit more complicated than that of most other viruses.

Number of genes of HIV:

HIV has just nine genes (compared to more than 500 genes in a bacterium, and around 20,000-25,000 in a human). Three of the HIV genes, called gag, pol and env, contain information needed to make structural proteins for new virus particles. The other six genes, known as tat, rev, nef, vif, vpr and vpu, code for proteins that control the ability of HIV to infect a cell, produce new copies of virus, or cause disease.

At either end of each strand of RNA is a sequence called the long terminal repeat, which helps to control HIV replication.

HIV life cycle:

Entry

HIV can only replicate (make new copies of itself) inside human cells. The process typically begins when a virus particle bumps into a cell that carries on its surface a special protein called CD4. The spikes on the surface of the virus particle stick to the CD4 and allow the viral envelope to fuse with the cell membrane. The contents of the HIV particle are then released into the cell, leaving the envelope behind.

Reverse Transcription and Integration

Once inside the cell, the HIV enzyme reverse transcriptase converts the viral RNA into DNA, which is compatible with human genetic material. This DNA is transported to the cell's nucleus, where it is spliced into the human DNA by the HIV enzyme integrase. Once integrated, the HIV DNA is known as provirus.

Transcription and Translation

HIV provirus may lie dormant within a cell for a long time. But when the cell becomes activated, it treats HIV genes in much the same way as human genes. First it converts them into messenger RNA (using human enzymes). Then the messenger RNA is transported outside the nucleus, and is used as a blueprint for producing new HIV proteins and enzymes.

Assembly, Budding and Maturation

 

This electron microscope photo shows newly formed HIV particles budding from a human cell.

Among the strands of messenger RNA produced by the cell are complete copies of HIV genetic material. These gather together with newly made HIV proteins and enzymes to form new viral particles, which are then released from the cell. The enzyme protease plays a vital role at this stage of the HIV life cycle by chopping up long strands of protein into smaller pieces, which are used to construct mature viral cores.

The newly matured HIV particles are ready to infect another cell and begin the replication process all over again. In this way the virus quickly spreads through the human body. And once a person is infected, they can pass HIV on to others in their bodily fluids.

Connection between HIV and AIDS:

HIV causes AIDS by damaging the immune system cells until the immune system can no longer fight off other infections that it would usually be able to prevent.

It takes around ten years on average for someone with HIV to develop AIDS. However, this average is based on the person with HIV having a reasonable diet, and someone who is malnourished may well progress from HIV to AIDS more rapidly.

Transmission of HIV:

HIV is found in the blood and the sexual fluids of an infected person, and in the breast milk of an infected woman. HIV transmission occurs when a sufficient quantity of these fluids get into someone else's bloodstream.

There are various ways a person can become infected with HIV:

• Unprotected sexual intercourse with an infected person: Sexual intercourse without a condom carries the risk of HIV infection.
• Contact with an infected person's blood: If sufficient blood from somebody who has HIV enters someone else's body, then HIV can be passed on in the blood.
• Use of infected blood products: Many people in the past have been infected with HIV by the use of blood transfusions and blood products which were contaminated with the virus. In much of the world this is no longer a significant risk, as blood donations are routinely tested for HIV.
• Injecting drugs: HIV can be passed on when injecting equipment that has been used by an infected person is then used by someone else. In many parts of the world, often because it is illegal to possess them, injecting equipment or works are shared.
• From mother to child: HIV can be transmitted from an infected woman to her baby during pregnancy, delivery and breastfeeding.

Certain groups of people, such as injecting drug users, sex workers, prisoners, and men who have sex with men have been particularly affected by HIV. However, HIV can infect anybody, and everyone needs to know how they can and can’t become infected with HIV.

HIV symptoms:

Some people experience a flu-like illness, develop a rash, or get swollen glands for a brief period soon after they become infected with HIV. However, although these are hiv symptoms they are also common symptoms of other less serious illnesses, and do not necessarily mean that a person has HIV.

Often people who are infected with HIV don’t have any symptoms at all. It is important to remember that a person who has HIV can pass on the virus immediately after becoming infected, even if they feel healthy. It’s not possible to tell just by looking if someone has been infected with HIV.

The only way to know for certain if someone is infected with HIV is for them to be tested.

Testing for HIV:

 

A sign promoting HIV testing in Livingstone, Zambia 

 

It is important for a person to get an HIV test if they think they may have been at risk of HIV infection.

There are various types of HIV test, but the most commonly used - the antibody or ELISA test - detects HIV antibodies in a person’s blood. It is necessary to wait at least 3 months after the last possible exposure before having an HIV antibody test, to be certain of an accurate result.

The prospect of receiving a positive test result (meaning that a person is infected with HIV) may be daunting, but learning that you are HIV positive is the first step to getting support and staying healthy. HIV testing is also very important for stopping the spread of HIV, as somebody who is aware of their HIV status can take steps to ensure they do not pass on the virus.

Treatment of HIV:

 

An HIV positive South African woman holding her antiretroviral drugs 

 

Antiretroviral drugs keep the levels of HIV in the body at a low level, so that the immune system is able to recover and work effectively. Antiretroviral drugs enable many HIV positive people to live long and healthy lives.

Starting antiretroviral treatment for HIV infection involves commitment – drugs have to be taken every day, and for the rest of a person’s life. Adhering to HIV treatment is important, particularly because not doing so increases the risk of drug resistance. Side effects to the HIV drugs can make adherence difficult, and are sometimes very severe. There are ways of reducing the impact of these side effects, but sometimes it is necessary to change to an alternative HIV treatment regime.

There are more than 20 antiretroviral drugs approved for the treatment of HIV infection in the US and Europe, as well as many new HIV drugs currently undergoing trials. Although treatment for HIV has become more widely available in recent years, access to antiretroviral treatment is limited in some parts of the world due to a lack of funding.

Prevention of HIV:

Despite considerable investment and research, there is currently no vaccine for HIV, and microbicides (designed to prevent HIV being passed on during sex) are still undergoing trials. However, there are other ways that people can protect themselves from HIV infection, which are the basis of HIV prevention efforts around the world.

Education about HIV and how it is spread is an essential part of HIV prevention. HIV education needs to be culturally appropriate and can take place in various settings, for example lessons at school, media campaigns, or peer education.

Preventing sexual transmission of HIV

 

HIV and AIDS education for Scouts in the Central African Republic 

 

If a person has sexual intercourse with someone who has HIV they can become infected. ‘Safer sex’ refers to things that a person can do to minimise their risk of HIV infection during sexual intercourse; most importantly, using condoms consistently and correctly.

A person can be certain that they are protected against HIV infection by choosing not to have sex at all, or by only doing things that do not involve any blood or sexual fluid from one person getting into another person's body. This kind of sexual activity is the only thing that can be considered ‘safe sex’.

Effective sex education is important for providing young people with the knowledge and skills to protect themselves from sexual transmission of HIV. Comprehensive sex education should develop skills and attitudes that encourage healthy sexual relationships, as well as provide detailed information about how to practise ‘safer sex’.

Preventing transmission of HIV through blood

A person can protect him or herself against HIV infection by ensuring that HIV infected blood does not enter their body.

Injecting drug users who share injecting equipment or works are at risk of HIV infection. Needle exchange programmes can help to prevent HIV transmission among drug users by providing clean needles and disposing of used ones.

Health care workers can be exposed to HIV infected blood while at work. The most effective way to limit their risk of HIV infection is to use universal precautions with every patient, for example washing hands and wearing protective barriers (gloves, aprons, goggles). In the event that a healthcare worker is exposed to potentially HIV infected blood at work, PEP (Post exposure prophylaxis) is recommended as an HIV prevention measure.

Preventing mother to child transmission of HIV

Mother to child transmission of HIV can be prevented by using antiretroviral drugs, which reduce the chances of a child becoming infected with HIV from around 25% to less than 2%. Once a child is born, safer infant feeding practices can also greatly reduce the risk of HIV being passed on from mother to child.

For these precautions to be taken, an HIV positive mother must firstly be aware of her status. This is why HIV testing in pregnancy is a crucial prevention measure.

The full story of HIV and AIDS

HIV is only half the story…

What happens when HIV develops into AIDS? Why are approximately 2 million people dying from AIDS each year? What are the effects of the global AIDS epidemic?

Learn about AIDS and get the full story.