An introduction to HIV and AIDS, including: definitions; the means by which HIV attacks the body and reproduces itself; the reasons why there is no cure for HIV; and the transition from HIV to AIDS.
HIV is a virus which can cause AIDS. HIV stands for Human Immunodeficiency Virus, so called because it attacks the immune system, the body’s defence against disease and infection.
AIDS stands for Acquired Immune Deficiency Syndrome. A person is said to have AIDS when the body’s immune system has become so weak that it can no longer fight off a range of diseases with which, under normal circumstances, it would be able to cope. These are termed opportunistic infections.
What is a virus?
A virus is a tiny organism which enters the body’s cells and uses them to make copies of itself. When the new copies of the virus break out of the host cell, they damage and usually destroy it.
The common cold, flu and warts are all caused by viruses, which, unlike bacteria – responsible for cholera and tetanus, for example – cannot be killed by antibiotics.
HIV is far more delicate than the cold viruses, which can be passed through the air when somebody sneezes. HIV can only survive in body fluids, especially blood and semen, and can only be passed from one person to another when the infected body fluids from one enter the other’s bloodstream.
How does HIV attack?
HIV attacks the white blood cells called T cells or CD4 cells, which coordinate the body’s immune system. Once inside, the virus integrates with the T cell’s genome and a cell which should normally fight infection becomes instead an HIV factory. The new viruses weaken and destroy the cell when they break out from it.
You will probably have heard that HIV is a retrovirus. What this means is that it consists of RNA molecules which transcribe into DNA molecules in order to integrate with the T cell. (It used to be thought that RNA was only produced by DNA – not vice versa.)
The practical consequence of this is that the virus mutates very quickly, since the ‘reverse transcription’ from RNA to DNA is unstable. This means the virus quickly grows resistant to the body’s natural antibodies and is why it can become resistant to anti-viral drugs. It is one of the main reasons why a vaccine has not yet been developed. It is also a reason why you should still practise safer sex even if you are HIV+ and having sex with another HIV+ person.
Why is there no cure for HIV?
Once you are infected with HIV, you are said to be and will (as yet) always be HIV+. This is because, even if drugs or the body’s immune system destroy every infected T cell which is actively producing HIV, and the copies of the virus in the bloodstream, there will be other infected T cells in which the virus is dormant and so effectively hidden. These infected cells will become active later.
It is also because, as we’ve said above, the virus mutates and changes its appearance very quickly. It can even split into two – it is made of two RNA molecules – and recombine with other split viruses to produce a slightly different virus.
While your body will have produced antibodies to attack the last type of HIV it detected, antibodies are very specialised and won’t recognise or be able to deal with the ‘new-look’ virus. By the time new antibodies have been produced, the virus will have multiplied hugely. In other words, HIV is always a step ahead.
The other, main, reason why HIV is hard to fight is that, as we’ve said, it attacks and hides within the immune system.
Why does HIV take so long to develop into AIDS?
Even without medical treatment, it can take years from the initial infection with HIV for a person to develop AIDS. This is because the immune system does fight back and is only very gradually worn down to the point where it is hopelessly weakened. One consequence of this is that there is a very large window of opportunity for the virus to spread between people.
It should be added that new variants of HIV have been observed which progress from initial diagnosis to death in a very short period – of around six months – and which have proven drug-resistant.