HIV

HIV has killed millions of people worldwide, and infected many more since it was first identified as a threat to public health more than 20 years ago.

Sub-Saharan Africa is thought to be most blighted by the virus, but it poses a huge problem across much of the developing world, where the latest drugs to control infection are not always readily available.

What is it?

HIV stands for Human Immunodeficiency Virus.

The virus is transmitted from person to person through blood and some other bodily fluids such as semen, vaginal secretions and breast milk.

The virus attacks the person's natural defence against disease - the immune system - weakening it over time.

In particular, HIV attacks one type of immune cell, known as a CD4 lymphocyte.

A person who has been infected with HIV is said to be HIV positive.

They are likely to become more ill with time as their immune system fails and is less able to fight off other illnesses.

When their immune system has become very damaged or they become sick with a number of particularly severe illnesses, usually around 10 years after they first became infected with HIV, they are said to have AIDS or Acquired Immune Deficiency Syndrome.

What are the symptoms?

Someone who is HIV positive may feel perfectly healthy and well and may not be aware that they have the virus.

Within a few weeks of infection with the virus, some may develop a flu-like illness or a rash or swollen glands.

A routine HIV test at this stage will not show that the person has the virus, however.

It is not until about three months after becoming infected that they will test HIV positive on an antibody test.

In the early disease, people who are HIV positive can develop illnesses that people with normal immune systems can also get, such as tuberculosis, malaria, blood poisoning and some skin infections.

However, individuals with HIV may take longer to recover.

With time - years if the person is otherwise healthy and well nourished - HIV weakens the immune system.

This makes people with HIV vulnerable to infections that healthy people would normally fight off easily.

These are called opportunistic infections and are caused by germs that are around us all the time. An example is thrush or candida.

Opportunistic infections can produce a wide range of symptoms, some of them severe.

Certain cancers can also develop and damage the skin, brain and nervous system.

Who is at risk?

Anyone who is exposed to the following can contract HIV:

• Unprotected sexual intercourse with an infected person - this includes oral sex
• Contact with infected blood - e.g. via a blood transfusion, injury
• From mother to child - during pregnancy, labour and breastfeeding
• Injecting drugs and sharing needles

A person cannot catch HIV from toilet seats, by hugging or by eating food prepared by someone who has HIV.

Globally, over 40 million people are living with HIV.

More than 25 million people have died of HIV/AIDS since 1981.

What is the outlook?

There is still no cure for HIV. However, the disease is no longer an imminent death sentence thanks to the major advances in HIV research and drug development over recent years.

With treatment, people with HIV can live for decades with the condition.

However, HIV medicines are not widely available in many poor countries around the world.

Millions of people are still dying prematurely from HIV/AIDS.

Of the 6.5 million people in developing and transitional countries who need life-saving AIDS drugs, only 1 million are receiving them.

How can it be treated?

The mainstay of treatment is with antiretroviral drugs. They will not cure HIV but can delay the onset of AIDS and help the person to remain healthy for longer.

There are four main groups of antiretroviral drugs. Each attacks HIV in a different way, but all work by stopping the virus from replicating:

• Non-Nucleoside Reverse Transcriptase Inhibitors - these block an enzyme, called reverse transcriptase, which HIV uses to make a DNA copy of itself once it has entered a human cell
• Nucleoside/Nucleotide Reverse Transcriptase Inhibitors - these make sure the DNA copy is faulty
• Protease Inhibitors - prevent the production of mature, infectious virus particles in infected human cells by blocking an enzyme called protease
• Fusion or Entry Inhibitors - stop HIV from entering human cells where they would replicate

A combination of a few of these drugs is usually recommended and they are taken for the rest of the person¿s life.

This combination, called HAART or highly active antiretroviral therapy, has improved life expectancy significantly.

Although they are very effective, antiretroviral drugs can have unwanted side effects such as nausea.

Also, the treatment may stop working if the virus mutates in a way that makes it resistant to the drugs.

Some combinations of antiretroviral treatments can also reduce the chance that a person who has been exposed to HIV will become infected.

This is called post-exposure prophylaxis and the drugs must be taken immediately after a person has been exposed to HIV - within hours preferably.

It is also possible to treat and even prevent some of the opportunistic infections that occur alongside HIV/AIDS.

Other important aspects of care include prevention of onwards transmission of HIV to others (between sexual partners and from mother to child, for example), regular testing of CD4 count to check how far the disease has progressed and what HIV treatment is needed, plus palliative care during the end stages of the disease.

Scientists are working to find a vaccine against HIV, but as yet no effective vaccine is available.