Dr Linda Fellowes, a biochemist at the Kew laboratories, said she was 'quietly optimistic' about the work done so far. 'At this stage nobody can talk about a cure for Aids. What we are looking at is maintenance of health in infected people.'
Following infection with the virus, there is a long incubation period of 8 to 10 years on average, when a person is healthy. After this there is a reduction in the number of white blood cells which are vital components of the immune system, and the onset of Aids. Some plant chemicals, known as sugar alkaloids, appear to stop HIV infecting more cells by bringing about changes in the viral coat. The virus can no longer 'lock on' to white blood cells and is prevented from infecting them.
The involvement of the laboratories at Kew in Aids research is the result of a 'large dose of serendipity', Dr Fellowes said. Alkaloids which had been isolated for different reasons - because they showed anti-insect activity - were sent to St Mary's Hospital, London, for further investigation.
'We had some alkaloids which appeared to have some anti-viral activity against the flu virus and so we threw those in too.' They were not very effective against flu but in large doses, they did appear to reduce the infectivity of HIV. Now Dr Fellowes and two colleagues are looking for similar chemicals in other plants and are trying to develop more potent forms which will inhibit the virus at lower doses. Their work is backed by the Medical Research Council.
In addition, the scientists are analysing reports on herbal medicines used in HIV disease. 'Most of these reports are anecdotal but some do come from very reliable sources,' Dr Fellowes said.
HIV has, so far, defied the best efforts of medical science. Finding a treatment among plants and herbs may seem unlikely, but about a quarter of modern drugs are derived from plants.
They include the heart drug digoxin, derived from digitalis, which is found in the leaves of plants of the foxglove family; reserpine, derived from the roots of certain species of Rauwolfia which is used to treat high blood pressure; and aspirin, which comes from the bark of the willow tree. Vincristine, used in cancer, is derived from the plant Vinca rosea. One potential Aids treatment, a modified form of a chemical derived from the Australian bean, is undergoing clinical trials in the United States.
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