This was the first time that wild migratory birds were found to be infected by this strain.Every winter we welcome feathered visitors with vividly colourful plumages from far-off lands. But this year they may bring the dreaded bird flu with them. Avian flu is an infectious disease of birds, caused by influenza type A strain of the virus. It was identified in Italy more than 100 years ago.

Crossover Bar-headed geese have already arrived at their wintering grounds near Cauvery River in Karnataka. Over the next 10 weeks, 100,000 geese, gulls, and cormorants will leave their summer home at Lake Qinghai and head for India, Bangladesh and Australia.

Should we worry about an epidemic in birds? Yes, two reasons make this epidemic a serious one. Earlier avian flu was known to attack poultry birds and pigs but no one reported an epidemic in wild birds. When domestic birds are infected it is possible to monitor them. But not so with the wild species. Many wild bird species are travellers and when the infected ones land at their winter homes in the Asian wetlands, the infection may spread to other birds who share the grounds. When these birds return they will again carry the virus to practically every corner of the world. The range of the disease will then span the globe.

Pandemics (global flu epidemics) start when a virus from a non-human species (pig or bird) affects human beings. Humans can’t fight the disease because they have no immunity against it. The 1918 pandemic Spanish Flu killed more people than did the guns of World War I. In 2004, scientists found evidence linking the epidemic to the H1N1 strain of avian flu.

Making the leap
Another disturbing factor is that genetic analysis has shown that the Qinghai Lake epidemic was caused by the H5N1 sub type of the virus. In 1997, scientists got the first proof of direct transmission from birds to humans when 18 people in Hong Kong were infected by the H5N1 strain. This outbreak was easily controlled because the virus lacks ability to spread from person to person. But that is small comfort. The virus could get better at infecting people because of its ability to mutate very quickly. As it is genetically unstable, this flu can mix its genes while reproducing inside a human cell and easily transform to a strain that could spread from person to person.

As the geographic range of H5N1 increases, more people will catch the flu, giving the virus more chances to mutate. The World Health Organisation fears that the virus is on the verge of transforming into a pandemic form, resembling the Spanish Flu that killed more than 20 – 40 million.

So far, India has remained insulated from bird flu. But for how long?