Avian influenza: The current perspectives
The avian influenza virus (AIV), belonging to genus Influenzavirus A of the family Orthomyxoviridae, is the causative agent of ‘bird flu’ or ‘avian flu’ that mainly affects domesticated birds with very high flock mortality. Free flying and aquatic birds are believed to be important reservoirs for the virus where usually it does not cause disease. On the basis of pathogenicity the disease is categorized into highly pathogenic avian influenza (HPAI) and low pathogenicity avian influenza (LPAI). The virus has caused severe disease outbreaks in domesticated poultry worldwide accounting for huge economic losses. HPAI is an extremely contagious, multi-organ systemic disease placed under “List A” disease of OIE, having the potential of very serious and rapid spread, irrespective of national borders, and of serious socio-economic or public health concern. Most AI viruses are of low pathogenicity and produce either subclinical infections or respiratory and/or reproductive diseases in a variety of domestic and other bird species. The AI virus H5N1 subtype, which has been limited to poultry, now has spread to migratory birds also and has emerged in mammals and among the human population too. This subtype, having a significant zoonotic potential, has caused several disease outbreaks in poultry in many Asian and few of the European countries leading to losses of more than 200 million birds and has claimed more than 70 human lives, indicating that this flu virus is now becoming more dangerous. HPAI has never been reported in the Indian sub-continent. Fortunately with this less number of human deaths, the virus has not yet acquired the ability of rapid human to human spread, which if happens, could trigger a deadly human pandemic like the human influenza pandemic during ‘Spanish flu’ of 1918. Extreme genetic variations exhibited by the virus make the disease difficult to be controlled. This highlights the importance of addressing the issue of bird flu globally and to frame out appropriate strategies for its timely prevention, control and eradication. Strict biosecurity measures, disease surveillance and judicious vaccination strategies are of paramount importance in preventing the disease in birds, limiting its epidemic potential and avoiding an imminent human pandemic. Effective vaccines for protecting birds as well as the humans against the H5N1 subtype virus are not available, for which the scientific community all over the world is trying to find out effective solutions exploiting the recent advances in vaccinology. This could prevent the financial losses to the poultry industry as well as save the precious lives of millions of people having put under a possible pandemic threat.
Avian influenza, bird flu, diagnosis, prevention, control, vaccines, biosecurity, zoonoses, pandemic.