What comes after phase six?

Swine flu declared pandemic, can be even deadlier

three months after it struck, who declared swine flu a global pandemic of the highest level: phase six. Known as the 2009 A (H1N1) virus, it took down 89,921 people across 85 countries in six continents. The death count was 382. Yet it could not match the lethality of the Spanish flu virus that affected one-third of the world's population when it struck in 1918. American researchers explained why. The swine flu virus cannot bind well to the human respiratory tract receptors, hence is inefficient at transmission.

A team led by Taronna R Maines from the National Center for Immunization and Respiratory Diseases under the Centers for Disease Control and Prevention in usa, studied the activity of the virus in ferrets and mice. They introduced three 2009 A (H1N1) virus strains into healthy ferrets.A day later more healthy ferrets were placed in their cages for direct contact and in adjacent cages with perforated walls that allowed respiratory droplets. They found the virus spread more rapidly via direct contact.

The results were then compared with the seasonal H1N1 viral infection in ferrets. Respiratory transmission was more effective in the seasonal flu virus. Tests on mice showed that compared to the common influenza virus, the swine flu virus adapted quickly to the host.

Through various tests the researchers confirmed that the binding affinity of the swine flu virus to receptors in the human respiratory tract was lower than that of the seasonal flu virus; only the binding pattern was similar. Hence during airborne transmission the chances of the virus infecting individuals decreased. But a single gene mutation can make the virus bind better to receptors, warned authors of the study published on July 2 in Science Express.