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genital tract, and other mucous membranes, to part company with each other, creating HIV-sized chinks in the body’s immunological armour. This allows the virus to penetrate and infect the susceptible immune cells that sit in the tissue below. Once inside these cells, the virus inserts a copy of its genetic material into the DNA of the cell. This is then used as a template to produce thousands of new virus particles which bud off to infect other cells around the body.
Part of the reason why HIV is so difficult to treat is that the virus uses as its genetic material a chemical relative of DNA called RNA. But unlike DNA, which contains two strands of information, one the mirror image – and effectively a back up – of the other, RNA contains just one single strand. With nothing to check the message against, the virus makes multiple genetic spelling mistakes when it copies itself, introducing mutations that canalter the appearance, virulence and drug-resistance profile of the virus.
To get around this problem, doctors now prescribe cocktails of different drugs which target the virus from several different biochemical directions at the same time. This approach, known as HAART (highly active anti-retroviral therapy) slows down the rate at which resistant mutants appear, helping patients to remain healthier for longer. But drug therapy is only a temporary solution and, owing to cost, one which is available only to a minority of those who are infected. Instead, what the world sorely needs is an effective AIDS vaccine.
So far this has proved impossible to achieve. One of the reasons for this is that to block HIV, the body needs to be able to produce antibodies capable of neutralising the viral velcro employed by HIV to lock onto and invade CD4 immune cells. But the virus keeps this part of its structure concealed beneath a meshwork of sugar molecules and only reveals its hand in the final moments asit infects a cell, making it very difficult for the immune system to intervene.
That said, scientists have found recently that some people can make antibodies capable of blocking this part of the virus, suggesting that if a vaccine can be produced to allow everyone to make these antibodies, then we may finally be looking at a way to stop the 7000 new cases of HIV that are being diagnosed daily.
In the meantime, apart from sending out clear safe-sex messages, a number of other anti-AIDS strategies are being investigated. One study carried out recently in South Africa by Salim Abdool Karim and his colleagues at the University of KwaZulu-Natal, Durban, 22 showed that a gel impregnated with the anti-HIV drug tenofovir and applied vaginally before and after sex reduced the rate of new HIV infections amongst the women using the gel by up to 50%.
Also, amongst men, researchers have shown convincingly that being circumcised can havean equally powerful protective effect; several studies have confirmed that circumcision cuts the HIV infection rate by over 60% in males who undergo the procedure. Removing the foreskin is probably protective because it reduces the mucosal surface area through which infection can occur and also leads to the virus becoming deactivated more quickly because there are fewer warm, wet recesses in which it can lurk.

A long-held view in cosmology circles is that the solar system, comprising the sun, the earth and all of our neighbouring planets, was catapulted into existence about four and a half billion years ago by the arrival of a huge shockwave. A nearby star that had reached the end of its life is thought to have blown itself to pieces in a catastrophic explosion known as a supernova, producing in the process a multimillion mile an hour maelstrom of dust and debris. This cannoned through space until it ran headlong into a cloud of swirling gas.
    This cloud would have been about 100 times the present earth–sun distance in diameter and would have weighed about three times as much as the sun. The arriving