Bird flu, also known as the avian influenza flu is one of the most recent worldwide health scare that is making its way all over the world. Avian bird flu is caused by the H5N1 virus, which naturally occurs in birds. Birds in the wild, all over the world, carry the virus in their intestines, although they rarely become ill from it.

The Avian bird flu however, is very contagious among birds and can spread to domesticated birds such as ducks and chickens and kills them. The bird flu is transmitted though saliva, nasal secretions and feces. Usually the bird flu is only transmitted from bird to bird, but cases have now been widely reported since 1997 of the flu being transmitted from bird to human, with cases reported of human-to-human transmission, although the virus has not infected more than one person in those cases.

Avian Bird Flu viruses are always changing, and over time may develop into a strain that can be transmitted from human to human to human, in which case we would be faced with a global pandemic of devastating proportions

Role of migratory birds

Scientists are increasingly convinced that at least some migratory waterfowl are now carrying the H5N1 virus in its highly pathogenic form, sometimes over long distances, and introducing the virus to poultry flocks in areas that lie along their migratory routes. Evidence supporting this altered role began to emerge in mid-2005 and has since been strengthened.

The die-off of more than 6000 migratory birds, infected with the highly pathogenic H5N1 virus that began at the Qinghai Lake nature reserve in central China in late April 2005 was highly unusual and probably unprecedented. Prior to that event, wild bird deaths from highly pathogenic avian influenza viruses were rare, usually occurring as isolated cases found within the flight distance of a poultry outbreak.

Transmission through humans

The virus can improve its transmissibility among humans via two principal mechanisms. The first is a resentment's event, in which genetic material is exchanged between human and avian viruses during co-infection of a human or pig. Resentment could result in a fully transmissible pandemic virus, announced by a sudden surge of cases with explosive spread.

The second mechanism is a more gradual process of adaptive mutation, whereby the capability of the virus to bind to human cells increases during subsequent infections of humans. Adaptive mutation, expressed initially as small clusters of human cases with some evidence of human-to-human transmission, would probably give the world some time to take defensive action, if detected sufficiently early.

Spread of the virus in different countries

The outbreaks of highly pathogenic H5N1 avian influenza that began in Southeast Asia in mid-2003 and have now spread to a few parts of Europe are the largest and most severe on record.

To date, nine Asian countries have reported outbreaks (listed in order of reporting): the Republic of Korea, Viet Nam, Japan, Thailand, Cambodia, the Lao People's Democratic Republic, Indonesia, China, and Malaysia. Of these, Japan, the Republic of Korea, and Malaysia have controlled their outbreaks and are now considered free of the disease.

The H5N1 virus has caused by far the greatest number of human cases of very severe disease and the greatest number of deaths. The H5N1 virus if given enough opportunities will develop the characteristics it needs to start influenza pandemic.