What is HIV?

HIV stands for Human Immunodeficiency Virus.  A virus can only survive by living in the cells of another organism. HIV is a type of virus called a retrovirus: It incorporates itself into the genetic material of cells called 'CD4 white blood cells', which are part of  the immune system.  This process is called 'reverse transcription', and it enables HIV to replicate.  This leads to destruction of the CD4 cells and damages the immune system.

What is AIDS?

AIDS stands for Acquired Immune Deficiency Syndrome.  A syndrome is a set of signs and symptoms that occur together, as a result of a specific cause.  The syndrome of AIDS is caused by HIV.  However a person infected with HIV may not necessarily progress to having AIDS.

HIV causes AIDS by damaging the immune system and making the body vulnerable to 'opportunistic infections'.  These are called ‘opportunistic’ because the weakened immune system gives them the ‘opportunity’ to take hold. These infections can cause death in people were severely weakened immune system.

AIDS was first diagnosed in 1981. Since then HIV and AIDS have spread rapidly and cases have been reported in more than 150 countries.  At the beginning of 2004 it was estimated that nearly 42,000,000 people were living with HIV and AIDS.

In Australia at the beginning of 2004, more than 20,000 people have been diagnosed with HIV infection. Over 8000 of these have been diagnosed with AIDS, and nearly 6000 people have died from AIDS related illnesses.

Different Stages if HIV/ AIDS

HIV infects cells in the immune system and the central nervous system. The main cell HIV infects is called a T helper lymphocyte. The T helper cell is a crucial cell in the immune system. It co-ordinates all other immune cells so any damage or loss of the T helper cell seriously affects the immune system.

HIV infects the T Helper cell because it has the protein CD4 on its surface. HIV needs to use CD4 to enter cells it infects. This is why the T helper cell is referred to as a CD4 lymphocyte. Once inside a T helper cell, HIV takes over the cell and the virus then replicates. In this process (which takes around a couple of days) the infected cell dies. New virus then seeks out new T helper cells to infect.

However, battling against this the immune system is rapidly killing HIV and HIV-infected cells, and replacing the T helper cells that have been lost.
HIV progression can generally be broken down into four distinct stages:

• Primary infection
• Clinically asymptomatic stage
• Symptomatic HIV infection
• Progression from HIV to AIDS.

STAGE 1 : Primary HIV Infection

This stage of infection lasts for a few weeks and is often accompanied by a short flu like illness which occurs just after infection. This flu like illness is sometimes referred to as seroconversion illness. In up to about 20% of people the symptoms are serious enough to consult a doctor, but the diagnosis is frequently missed. Even if an HIV antibody test is done at this time, it may not yet be positive.
During this stage there is a large amount of HIV in the peripheral blood and the immune system begins to respond to the virus by producing HIV antibody and cytotoxic lymphocytes.

STAGE 2 : Clinically Asymptomatic Stage

This stage lasts for an average of ten years and, as its name suggests, is free from any symptoms, although there may be swollen glands.The level of HIV in the peripheral blood drops to very low levels but people remain infectious and HIV antibodies are detectable in the blood, so antibody tests will show a positive result.
Recent research has shown that HIV is not dormant during this stage, but is very active in the lymph nodes. Large amounts of T helper cells are infected and die and a large amount of virus is produced.

A test is available to measure the small amount of HIV that escapes the lymph nodes. This test which measures HIV RNA (HIV genetic material) is referred to as the viral load test, and it has an important role in the treatment of HIV infection.

STAGE 3 : Symptomatic HIV Infection 

 Over time the immune system loses the struggle to contain HIV. This is for three main reasons:
• The lymph nodes and tissues become damaged or 'burnt out' because of the years of activity;
• HIV mutates and becomes more pathogenic, in other words stronger and more varied, leading to more T helper cell destruction;
• The body fails to keep up with replacing the T helper cells that are lost.
As the immune system fails, so symptoms develop. Initially many of the symptoms are mild, but as the immune system deteriorates the symptoms worsen.

Where do opportunistic infections and cancers occur?

Symptomatic HIV infection is mainly caused by the emergence of opportunistic infections and cancers that normally the immune system would prevent. These can occur in almost all the body systems, but common examples are featured in the table below.
As the table below indicates, symptomatic HIV infection is often characterised by multi-system disease. Treatment for the specific infection or cancer is often carried out, but the underlying cause is the action of HIV as it erodes the immune system. Unless HIV itself can be slowed down the symptoms of immune suppression will continue to worsen.
 

STAGE 4 : Progression from HIV to AIDS 

As the immune system becomes more and more damaged the illnesses that present become more and more severe leading eventually to an AIDS diagnosis.
At present in the UK an AIDS diagnosis is confirmed if a person with HIV develops one or more of a specific number of severe opportunistic infections or cancers. However people can still be very ill with HIV but not have an AIDS diagnosis.

How is HIV transmitted?

Unprotected sexual contact or sharing drug injecting equipment are the most common causes of HIV transmission. Sexual contact that may transmit HIV includes vaginal and anal sex, and with lower associated risk, oral sex.

In a some cases, HIV can be transmitted from pregnant mother to child. This is called ‘vertical transmission’. The risk of vertical transmission can be reduced if the mother uses anti-HIV drugs during pregnancy and delivery. In Australia breast feeding is not recommended for mothers infected with HIV because of the risk of HIV being transmitted through breast milk.

Healthcare workers and emergency personnel are at low risk of acquiring HIV from workplace exposure to HIV (for example by needlestick injury). A drug treatment regime called Post Exposure Prophylaxis (‘PEP’) has been shown to be effective in preventing seroconversion to HIV in these circumstances.

Blood products have been screened for HIV in Australia since 1985 and receiving transfusions of blood products is considered safe.

There is no evidence of transmission of HIV through ordinary social contact. HIV is not transmitted through sharing of plates, cups, cutlery, swimming pools or toilets, kissing, coughing, sneezing or spitting . The necessary conditions for HIV transmission (see below) are not present in these situations.

The principles of HIV transmission

Transmission of HIV is dependant on a number of conditions being fulfilled.  Understanding these conditions gives a better understanding of how HIV is transmitted:

Firstly there must be a source of HIV infection.  HIV exists in certain bodily fluids of persons infected with HIV.  These include blood, semen, vaginal fluid and  breast milk.

Secondly, there must be a way for HIV to be transmitted to the bloodstream of an uninfected person.  Sexual contact, or sharing drug-injecting equipment are the most common routes of HIV transmission.

Thirdly, there must be a person susceptible for infection.  HIV transmission only takes place from one human to another.  Mosquitoes, for instance cannot become infected with HIV and pass it on to humans.

Finally, a sufficient amount of HIV must enter the blood of an uninfected person for infection to be established.  If insufficient HIV enters the bloodstream, transmission of HIV infection will not occur.
If these conditions are not fulfilled, HIV transmission does not take place.

Prevention of AIDS 

HIV can be transmitted in the sexual fluids, blood or breast milk of an infected person. HIV prevention therefore involves a wide range of activities including prevention of mother-to-child transmission, harm reduction for injecting drug users, and precautions for health care workers.

Treatment of AIDS 

Treatment and care consists of a number of different elements including voluntary counselling and testing (VCT), food and nutrition, support for the prevention of onward transmission of HIV, follow-up counselling, protection from stigma and discrimination, spiritual support, the provision of antiretrovirals (ARVs), treatment of STIs, management of nutritional effects, prevention and treatment of opportunistic infections (OIs), traditional treatment, palliative care, preparing for death, family and orphan support.

HIV positive people have differing needs according to the stage of their infection. The first stage is when people are asymptomatic, that is when they have no signs/symptoms of their infection. The second stage is when people have symptoms of HIV infection. The third stage relates to support and care of people who are terminally ill and nearing the end of their life.

The different aspects of care and support are all generally described at the first point at which they are needed. For example, VCT should ideally be provided at the asymptomatic stage, but it may also be needed at a later stage for those who did not wish to be tested earlier.