HIV / AIDS
36 million people worldwide are estimated to be living with HIV or AIDS. That's twice the population of Australia. Approximately 1/100 people worldwide aged 15 to 40 are infected.
AIDS is a disease caused by the destruction of the immune system by infection with a virus called HIV (HTLV-III or human immunodeficiency virus), which was identified in France in 1983 and the USA in 1984.
People infected with HIV gradually lose immune function, making them vulnerable to pneumonia, fungus infections, cancers and other common ailments. Without treatment there is slow progression, weight loss, debilitation and eventually death due to opportunistic infections or cancers. The progression from HIV infection to the clinical diseases that define AIDS may take six to ten years or more.
Causes and Risk Factors
HIV can be spread by unprotected sexual intercourse or through blood to blood contact e.g. sharing of needles among injecting drug users. In the past, before screening was introduced, this also occurred through blood transfusions or from infected blood products such as the Factor VIII used to treat hemophilia. HIV can also be spread from mother to child during pregnancy, at birth or breastfeeding or by accidental needle stick injury from a contaminated needle (occupational exposure). Coughing, sneezing, touch or insects do not spread HIV. PREVENTION is the best cure: awareness of the risk, education, safe sex practice and needle exchange schemes.
Diagnosis and Screening
Usually, HIV infection is detected by an HIV antibody test. The first test to be done, usually on blood, but possibly on saliva, is an ELISA (enzyme linked immunosorbent assay). Since this test can sometimes be positive even when someone is not infected (a `false positive'), such tests are repeated to confirm a positive reaction and subsequent tests may be done. There are also a number of tests that can look for the virus or parts of the virus itself, or damage to the immune system, or other aspects of the body's response to the effects of the virus.
HIV/AIDS progression can be monitored using surrogate markers (laboratory data that correlate with disease progression) or clinical endpoints (illnesses that are associated with more advanced disease). Surrogate markers for the various stages of HIV disease include the declining number of T-lymphocytes (CD4+ cells) and the amount of virus in the bloodstream (Viral load). Viral load tests count the number of HIV particles in a sample of blood. The result of a viral load test is described as the number of 'copies' of HIV RNA per milliliter (copies/ml). 10,000 copies/ml or lower is generally considered `low' and 50,000 copies/ml or greater is `high'.
Treatment with an effective anti-HIV regimen results in a fall in viral load and improvement in immune function. A `baseline' viral load test will be taken before starting treatment or a change in drug therapy followed by a second test a month or so later. People with 'undetectable' viral load remain infectious to others.
CD4 cells -T-cells (or T-lymphocytes) are white blood cells. There are two main types of T-cells. One type has CD4 receptors on its surface; these `helper' cells orchestrate the body's response to certain microorganisms such as viruses. The other T-cells called CD8, destroy infected cells and produce antiviral substances. HIV is able to attach itself to the CD4 molecule, allowing the virus to enter and infect these cells. During HIV infection approximately 1 billion CD4 cells are produced and destroyed daily. This results in a continuous loss of CD4 cells over time (~10 percent / year) which destroys the immune system over time.
A normal CD4 count in a healthy, HIV-negative adult is usually between 600 and 1200 CD4 cells/ml. In order to help understand changes in absolute CD4 count, what proportion of all lymphocytes are CD4 cells may be assessed. In HIV-negative people a normal result is around 40 per cent. A CD4 count, which falls below about 15 per cent, is understood to reflect a risk of serious infections. If the CD4 count is persistently below 350 cells/ml there is an increased risk of infection. If it drops below 200-250 there is an increased risk from serious infections.
Changes in viral load over time, along with CD4 count and symptoms can help to decide whether or not to start anti-HIV treatment. Other tests may also be carried out during HIV infection.
Management
The most effective way of using anti-HIV drugs is in combinations. Studies suggest that triple-drug combinations may have better anti-HIV effects than two drug regimens. This has now been called HAART (Highly Active Antiretroviral Therapy) and is the standard of care for treating HIV.