Is AIDS taking over the world?
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A disease is an abnormality of an animal or plant, caused by a pathogenic organism.
Therefore, disease resistance is the ability to withstand the attack of these pathogens and remain virtually unaffected. The disease may be infectious (communicable), caused by invading organisms that live parasitically on or within the body. The disease causing organisms include viruses, some bacteria and certain other organisms that may be passed from person to person – e.g. Plasmodium that causes malaria. Other types of communicable disorders are fungal, bacterial and viral diseases. The alternative type of disease to the contagious sorts above, are non-communicable disorders, which are not infectious. These can be caused by unfavourable environmental conditions. Cancer, allergies, genetic diseases and mental disorders all fall into this category.
AIDS is a viral infection, caused by an RNA retrovirus. A virus consists of a strand of nucleic acid (in this case RNA), wrapped in a capsid (a protein coat). The AIDS virus has an external envelope, made of lipid and protein. This envelope is derived from the cell membrane of the host cell in which the virus replicated. The virus contains reverse transcriptase enzyme.
AIDS stands for Acquired Immune Deficiency Syndrome; meaning that one is able to catch it, it is a weakness in the body’s system that fights diseases, and is a group of health problems that makes up a disease. A virus called HIV (Human Immunodeficiency Virus) causes AIDS. If the body is effected, it will try to fight the infection. The immune system will produce antibodies, which are special molecules in the blood with the function to attack foreign bacteria or viruses. They attack antigens in a number of ways, by: making them clump together, neutralising the toxins released, reacting with the bacterial cells so as to ensure attachment to the phagocytes, and also damaging the cell wall using hydrogen peroxide.7
The HIV virus is passed from one person to another via blood-to-blood or sexual contact. In addition, infected pregnant women can pass HIV to their babies during pregnancy or delivery, as well as through breast-feeding. The virus is transmitted in body fluids: blood, semen, vaginal fluid, breast milk and other blood containing fluids have all been proven to carry spread the virus.
By killing or impairing cells of the immune system, HIV progressively destroys the body’s ability to fight infections and certain cancers.
Individuals diagnosed with AIDS are susceptible to life-threatening diseases called opportunistic infections, which are usually caused by microbes that usually don’t cause illness in healthy people. In people with AIDS, these infections are often severe and sometimes fatal, because the immune system is so ravaged by HIV that the body can’t fight off certain bacteria, viruses and other microbes. The HHV virus (herpes) infects the same cells as the HIV virus, but infection with HHV will not lead to the development of AIDS.
HIV infects the positive subset of T-cells (lymphocytes), eventually leading to their depletion and the onset of various opportunistic infections manifested in AIDS. T and B-lymphocytes begin development within the bone marrow, and then move else where to continue their growth. B cells mature mostly within the bone marrow but complete the growth stage in the spleen. T cells leave the bone marrow for maturing in the thymus tissue, and then complete growth in the spleen. Both then migrate through the blood, via lymphatic vessels, to sites of inflammation and to the lymph nodes.
B cells release the antibody, which attaches to the outer covering of the antigen, marking it for destruction. T cells attack the tagged antigen and also stimulate B cells into action. Once the body has produced antibodies to a specific micro-organism, it generally is immune to future invasions by that organism. That is why people who have had chicken pox, as a child will not get the disease again as an adult.3 However, this seems not to be the case with the AIDS infection, as recent medical reports suggest that antigen presentation to T-cells by dendritic cells (antigen-presenting) may play an important role in the spreading of the HIV infection. In 1993, the Centres for Disease Control and Prevention (CDC) revised its definition of AIDS to include “all HIV infected individuals who have fewer than 200 CD4 T cells”.5
Some HIV positive people survive for decades, because of the affects of evolution. Their luck stems from inherited diversity, and they tend to carry certain forms of the receptor lock into which the HIV key fits so that the virus finds it hard to break into the cells.1 One person in six inherits an altered form of part of the defence mechanism. The onset of symptoms, for them, is delayed for a matter of years. But, an even more fortunate five- percent of humans has two copies of the altered gene, which results in the virus being blocked out altogether.
Because the HIV infection often causes no symptoms, a doctor will be testing a person’s blood for the presence of antibodies to HIV. HIV antibodies generally don’t reach levels in the blood which the doctor can see until at least a month following infection, and it may take antibodies as long as six months to show up in standard blood tests.
Since the discovery of AIDS in San Francisco, in 1981, there has been far stretching research into a cure and vaccination for the virus, which has caused a pandemic of a global scale. The Food and Drug Administration has approved a number of drugs for the treatment of the HIV infection, called NRTIs (Nucleotide Analogue Reverse Transcriptive Inhibitors).6 These drugs interrupt an early stage of virus replication. Although these drugs slow the spread of HIV in the body and delay the onset of opportunistic infections, they don’t prevent the transmission of HIV to other individuals. To add to this, currently available antiretroviral drugs do not cure people of the HIV infection or AIDS, and they all have side effects that can be severe. AZT (zidovudine) may cause the depletion of red or white blood cells, especially when supplemented into a program of protease inhibitors.
Researchers have credited highly active antiretroviral therapy, HAART, as being a major factor in reducing the number of deaths from AIDS in this country by 47% in 1997. This treatment involves a combination of reverse transcriptase inhibitors and protease inhibitors. NIAID-supported investigators are conducting an abundance of research into HIV vaccines and new therapies for the disease and some of its associated conditions. Researchers are beginning to discover exactly how HIV damages the immune system. This research is suggesting new and more effective targets for drugs and vaccines, so that one day it may be possible to prevent the transmission of AIDS completely.
1 Almost Like a Whale, Steve Jones, Flame, 1999
2 The Origin of the Species, Charles Darwin
3 Introduction to Advanced Biology, C J Clegg, John Murray Publishers Ltd., 2000
4 Introducing Immunology, Keith James, Gower Medical Publishing, 1985
5 HIV-1 Infection, Emily Platt, www.aegis.org/pubs
6 Viral Entry Discovery Suggests New Treatments, Theo Smart, GMHC, 1995
7 What is HIV and AIDS, www.bbc.co.uk/worldservice/sci_tec/features