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Scientists hail breakthrough in fight against deadly Ebola virus

Scientists have developed a new kind of "antisense" drug that has produced promising results in laboratory trials involving the Ebola and Marburg viruses, two of the most lethal known. The drug works by blocking the critical genes that the viruses use to replicate quickly inside the body to give patients valuable time to mount their own immune defence against the viral haemorrhagic fevers.

Tests on laboratory animals have shown that the antisense drugs are effective at fending off Ebola and Marburg, which cause rapid and intense fever and internal bleeding fatal in about 90 per cent of cases.

There are at present no effective treatments or vaccines against either of the viruses, which are highly infectious and have caused particular concern because of the possibility of them being used in biowarfare or as a terrorist weapon. The antisense drugs are composed of short strands of nucleic acids which form a sequence that is complementary or opposite to the nucleic acid sequence found in the genes of the viruses. They work by binding to the viral genes and blocking their action, giving time for the immune defences of the patients to launch an attack on the invading viruses, the scientists said.

The researchers, from the US Army Medical Research Institute of Infectious Diseases (Usamriid), report in the journal Nature Medicine that an antisense drug called AVI-6002 resulted in a survival rate of better than 90 per cent in laboratory mice and guinea pigs exposed to the Ebola virus. When the scientists tested the drug on laboratory monkeys, three out of five survived.

A similar antisense drug, called AVI-6003, proved even more successful against the Marburg virus, with every one of the treated monkeys surviving a viral attack, the study showed.

Ebola and Marburg are considered so dangerous that the research had to be done in special laboratories with the highest security classification, known as biosafety level 4, where the scientists had to wear space-suits and breathe filtered air to protect them as they did their experiments.

The scientists, led by Travis Warren of the Usamriid, believe the results are good enough to warrant clinical trials in humans and the US Food and Drug Administration has given permission to proceed.

The scientists said they have developed "human-grade" antisense drugs that could be used on people after an emergency in 2004, when a laboratory worker in the Usamriid was accidentally pricked in the thumb with a needle while treating Ebola-infected mice. The female worker was isolated, but found to be uninfected, so the human-grade antisense drug was not used on her. But the facility has worked with biotechnology company AVI BioPharma to develop antisense drugs to be used in human clinical trials.