What is HIV?
HIV stands for ‘human immunodeficiency virus’. HIV is a virus (of the type called retrovirus) that infects cells of the human immune system (mainly CD4 positive T cells and macrophages—key components of the cellular immune system), and destroys or impairs their function. Infection with this virus results in the progressive deterioration of the immune system, leading to ‘immune deficiency’. The immune system is considered deficient when it can no longer fulfill its role of fighting off infections and diseases.
Immunodeficient people are more susceptible to a wide range of infections, most of which are rare among people without immune deficiency. Infections associated with severe immunodeficiency are known as ‘opportunistic infections’, because they take advantage of a weakened immune system.
What is AIDS?
AIDS stands for ‘acquired immunodeficiency syndrome’ and is a surveillance definition based on signs, symptoms, infections, and cancers associated with the deficiency of the immune system that stems from infection with HIV.
What are the symptoms of HIV?
Most people infected with HIV do not know that they have become infected, because they do not feel ill immediately after infection. However, some people at the time of seroconversion develop “Acute retroviral syndrome” which is a glandular fever-like illness with fever, rash, joint pains and enlarged lymph nodes.
Seroconversion refers to the development of antibodies to HIV and usually takes place between 1 and 6 weeks after HIV infection has happened. Whether or not HIV infection causes initial symptoms, an HIV-infected person is highly infectious during this initial period and can transmit the virus to another person.
The only way to determine whether HIV is present in a person’s body is by testing for HIV antibodies or for HIV itself. After HIV has caused progressive deterioration of the immune system, increased susceptibility to infections may lead to symptoms. HIV is staged on the basis of certain signs, symptoms, infections, and cancers grouped by the World Health Organization (WHO).
What are the stages of HIV?
There are four stages of HIV which is characterised by Primary Infection Stage which is stage one, stage 2 is the Clinically Asymptomatic stage, stage 3, the Symptomatic Infection Stage and the final stage, stage 4- The Progression from HIV to AIDS.
This stage of infection lasts for a few weeks and is often accompanied by a short flu-like illness. In up to about 20% of people the HIV symptoms are serious enough to consult a doctor, but the diagnosis of HIV infection is frequently missed.
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 antibodies and cytotoxic lymphocytes. This process is known as seroconversion. If an HIV antibody test is done before seroconversion is complete then it may not be positive.
This stage lasts for an average of ten years and, as its name suggests, is free from major 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.
Research has shown that HIV is not dormant during this stage, but is very active in the lymph nodes. 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.
Over time the immune system becomes severely damaged by HIV. This is thought to happen for three main reasons:
Anti-retroviral treatment is usually started once an individuals CD4 count (the number of T helper cells) drops to a low level, an indication that the immune system is deteriorating. Treatment can stop HIV from damaging the immune system, therefore, HIV-infected individuals on treatment usually remain clinically asymptomatic.
However, in HIV-infected individuals not receiving treatment or on treatment that is not working, the immune system fails and symptoms develop. Initially many of the symptoms are mild, but as the immune system deteriorates the symptoms worsen.
Symptomatic HIV infection is mainly caused by the emergence of certain opportunistic infections that the immune system would normally prevent. This stage of HIV infection is often characterised by multi-system disease and infections can occur in almost all body systems.
Treatment for the specific infection 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.
As the immune system becomes more and more damaged the individual may develop increasingly severe opportunistic infections and cancers, leading eventually to an AIDS diagnosis.
A clinical criteria is used by WHO to diagnose the progression to AIDS, this differs slightly between adults and children under five. In adults and children (aged 5 or over) the progression to AIDS is diagnosed when any condition listed in clinical stage 4 is diagnosed and/or the CD4 count is less than 200 cells/mm3 or a CD4 percentage less than 15. In children younger than five, an AIDS diagnosis is based on having any stage 4 condition and/or a CD4 percentage less than 20 (children aged 12-35 months) and a CD4 percentage less than 25 (children less than 12 months). The criteria for diagnosing AIDS may differ depending on individual country guidelines.
Interim WHO clinical staging of HIV/AIDS and HIV/AIDS case definitions for surveillance (2005): http://www.who.int/hiv/pub/guidelines/clinicalstaging.pdf:2
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