PARIS - AN EXPERIMENTAL drug tested on lab animals has shown remarkable success in tackling two viruses, including a close cousin to a feared bioterror pathogen, a study published on Sunday said.

The drug, bavituximab, takes a novel tack in confronting viruses, which are notorious for mutations that evade or resist conventional pharmaceutical molecules.

Instead of confronting the intruder head-on, bavituximab waits until the virus has infected the cell.

At that point, a fatty molecule called phosphatidylserine, which is normally positioned on the cell wall's internal surface, flips to the outside of the cell.

Bavituximab then latches onto the phosphatidylserine, sending a red flag to the body's immune system to dispatch white blood cells to destroy the infected cell.

In a study in Nature Medicine, published by the London-based Nature group, bavituximab was put through its paces among guinea pigs infected with Pichinde virus - a close relative of the Lassa fever virus, considered a potential bioterror weapon by the Pentagon.

Animals that had not been inoculated with bavituximab were all killed; those who had received the injection had a 50 per cent survival rate. By giving the bavituximab group an addition injection with a standard anti-virus drug called ribavirin, the survival rate rose to 63 per cent.

The drug also provided 100 per cent protection amongst mice exposed to a virus called cytomegalovirus (CMV), whereas only 25 per cent of untreated animals survived.

Co-author Philip Thorpe, a professor of pharmacology at UT Southwestern Medical Center in Texas, said the findings were exciting, for they raised the prospect of a 'completely new class' of anti-viral drugs that may also sidestep the problem of mutation.

'By targeting a property of the host cell rather than the virus itself, anti-PS antibodies have the potential to treat a range of viral infections,' he said in a press release.

'They should be less susceptible to the viral mutations that contribute to the development of drug resistance.'

Bavituximab, a monoclonal antibody, is currently in clinical trials by Peregrine Pharmaceuticals of California to treat patients with hepatitis C.

Previous research has shown that phosphatidylserine-flipping occurs in cells infected with influenza, the herpes simplex virus, viruses in the families of the smallpox and rabies viruses as well as HIV, UT Southwestern Medical Centre said. -- AFP