What is AIDS and HIV?
HIV is a virus. Viruses infect the cells of living organisms and replicate within those cells. A virus can damage the cells it replicates in, which is one of the things that can make an infected creature become ill.
People can become infected with HIV from other people who already have it, and when they are infected they can then go on to infect other people. Basically, this is how HIV is spread.
HIV stands for the 'Human Immunodeficiency Virus'. Someone who is infected with HIV is said to be 'HIV+' or 'HIV positive'.
A damaged immune system is not only more vulnerable to HIV, but also to the attacks of other infections. It won't always have the strength to fight off things that wouldn't have bothered it before.
As time goes by, a person who has been infected with HIV is likely to become ill more and more often until, usually several years after infection, they become ill with one of a number of particularly severe illnesses. It is at this point that they are said to have AIDS - when they first become seriously ill, or when the number of immune system cells left in the body drops below a particular point. Different countries have slightly different ways of defining the point at which a person is said to have AIDS rather than HIV.
AIDS (Acquired Immune Deficiency Syndrome) is an extremely serious condition, and at this stage the body has very little defence against any sort of infection.
Without drug treatment, HIV usually progresses to AIDS in an average of ten years. This average, though, is based on a person having a reasonable diet. Someone in a resource-poor area who might not be adequately nourished may well progress to AIDS and death much more rapidly.
The Origin
The origin of AIDS and HIV has puzzled scientists ever since the illness first came to light in the early 1980s. For over twenty years it has been the subject of fierce debate and the cause of countless arguments, with everything from a promiscuous flight attendant to a suspect vaccine programme being blamed. So what is the truth? Just where did AIDS come from?
The first recognised cases of AIDS occurred in the USA in the early 1980s. A number of homosexual men in New York and San Francisco suddenly began to develop rare opportunistic infections and cancers that seemed stubbornly resistant to any treatment. At this time, AIDS did not yet have a name, but it quickly became obvious that all the men were suffering from a common syndrome. The discovery of HIV, the Human Immunodeficiency Virus that causes AIDS was made soon after. While some were initially resistant to the connection (and indeed remain so today), there is now clear evidence to prove that HIV does cause AIDS. So, in order to find the source of AIDS, it is necessary to look for the origin of HIV.
The 'Hunter' Theory
The most commonly accepted theory is that of the 'hunter'. In this scenario, SIVcpz was transferred to humans as a result of chimps being killed and eaten or their blood getting into cuts or wounds on the hunter. Normally the hunter's body would have fought off SIV, but on a few occasions it adapted itself within its new human host and become HIV-1. The fact that there were several different early strains of HIV, each with a slightly different genetic make-up (the most common of which was HIV-1 group M), would support this theory: every time it passed from a chimpanzee to a man, it would have developed in a slightly different way within his body, and thus produced a slightly different strain.
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