Key to flu virus identified


London - A major breakthrough in understanding what turns a normal flu virus into a mass killer was announced by scientists yesterday. The discovery may help doctors target potentially deadly viruses before they get out of control.

The worst episode in history was the 1918 Spanish 'Flu pandemic in which between 20 and 40 million people died.

Scientists studying a descendant of the 1918 virus said they had identified a molecular mechanism that marked it out as deadly.

The virus had a unique "key" which unlocked the door to cells throughout the body, enabling it to replicate in many different organs. Normally influenza is confined to cells within the respiratory system.

The discovery concerns proteins on the surface of the virus that allow it to attach to target cells.

Normally one of these proteins, called hemagglutinin, must be chopped into two parts before the virus can infect a cell. The virus uses enzymes from the cells it is invading as "scissors" to cut the protein.

These protease enzymes are usually found in the lungs and trachea, which is why influenza tends to be confined to that part of the body.

But in the strain studied by the scientists a different mechanism was at work that allowed the virus greater freedom of movement.