As of March 2005 many countries are stock piling antiviral drugs to prevent widespread devastation which could be caused by a flu pandemic.Experts say a pandemic is inevitable and will probably emerge in Asia if bird flu mutates with human flu, creating a highly pathogenic new virus. Bird flu viruses normally infect only birds and pigs. There are 15 different strains of the bird flu virus. Since 1959 viruses of the H5, H7 and H9 subtypes have crossed the species barrier to infect humans on 10 occasions.
Most bird flu viruses affecting humans have caused mild respiratory symptoms or conjunctivitis, with one exception the H5N1 strain. The H5N1 strain has caused severe disease with high fatality in 1997, 2003, 2005 and 2005. Studies have shown that the H5N1 strain has, over the years, become progressively more pathogenic and is now much hardier than in the past . It also seems to be expanding its host range to other mammals including species not previously thought to be susceptible to the virus such as tigers and leopards.The outbreaks of highly pathogenic H5N1 bird flu in poultry that began in Asia in 2003 have to date (end of October 2005), The H5N1 strain has killed more than 60 people in South East Asia since 2003. However, of those only one is suspected to have died after catching the virus from another human.
The majority of the cases have occurred in previously healthy children and young adults. The H5N1 strain remained largely in South-East Asia until this summer, when Russia and Kazakhstan both reported outbreaks Scientists fear it may be carried by migrating birds to Europe and Africa but say it is hard to prove a direct link with bird migration, although more swans have been found with bird flu in the Danube delta area in Romania.
