A world-renowned Aids expert has teamed up with Hong Kong scientists to develop a drug that they believe may be able to block the Sars virus. David Ho Ta-yi, the American-Chinese who helped pioneer a treatment for Aids, said yesterday scientists were testing synthetic peptides aimed at stopping the Sars virus penetrating human cells. Peptides, compounds made up of amino acids, were developed after the scientists noticed that the Sars virus attacked the human host in much the same way as HIV. Dr Ho, scientific director of the Aaron Diamond Aids Research Centre at the Rockefeller University in New York, said: 'There is an Aids drug that works by this sort of mechanism. By simply analysing the [Sars virus] sequence we were able to generate these peptides and test them. In the laboratory, at least, they do block the virus.' The scientists found that the virus uses two surface structures to lock on to human cells to infect them. The key is to design peptides that block the fusion process. The 'designer peptides' were developed on Monday, and on Wednesday tested on cultured cells to see if they blocked the ability of the virus to get inside the cells. 'We are certainly pleased with the results that several of the peptides actually protected the cells from the Sars virus infection,'' Dr Ho said. However, he stressed: 'We're not saying this is the drug to treat patients tomorrow.' Doctors have been using a combination of the antiviral drug Ribavirin and steroids to treat Hong Kong's 1,678 patients but up to 20 per cent have not responded. A total of 215 people have died. Malik Peiris, chief of virology at the University of Hong Kong, said some signatures in the Sars virus were similar to HIV. 'We are now at the stage of having drugs designed to target specifically vulnerable stages of the virus's life cycle.' The team is also working on a vaccine against Sars.