Bird Flu

The term bird flu or Avian flu is one and the same thing. They are used to describe the flu viruses that infect primarily the birds' population. In fact, birds appear to be a natural reservoir of flu viruses - 15 subtypes flu A virus are known to be circulating in bird populations.

All birds are thought to be susceptible to the avian influenza, though some species, such as wild ducks, are more resistant than others. Domestic poultry, such as chickens or turkeys, are particularly susceptible. The infection triggers a wide spectrum of symptoms in birds, ranging from mild illness to a highly contagious and rapidly fatal disease resulting in severe epidemics.

Bird Flu viruses infect wild bird populations, particularly water birds, typically without causing symptoms. The virus spreads through bird feces and contaminated water or dust. When Bird Flu spreads to poultry or other birds, it can cause more severe disease. Outbreaks of Bird flu have been recognized in poultry flocks in most countries of the world for many years.

Flu viruses that infect birds are called Bird flu viruses. Only flu A viruses infect birds, and all known subtypes of flu A viruses can infect birds. However, there are substantial genetic differences between the subtypes that typically infect both people and birds. Within subtypes of Bird flu type A viruses there also are different strains.

Bird flu A H5 and H7 viruses can have either "low pathogenic" and "high pathogenic" forms based on the genetic features of the virus and the severity of the illness they cause in poultry. Flu H9 virus has been identified only in a "low pathogenicity" form. Each of these three Bird flu A viruses (H5, H7, and H9) can be partnered with any one of nine neuraminidase surface proteins; thus, there are potentially nine different forms of each subtype (e.g., H5N1, H5N2, H5N3, H5N9).

The most prominent of these subtypes are Flu A H5, A H7 and A H9, each having potentially nine different types. Flu A H9 can be only in low pathogenic form. Flu A H5 and Flu A H7 can be highly pathogenic or low pathogenic.

H5 infections have been documented among humans, sometimes causing severe illness and death. H7 infection in humans is rare, but can occur among persons who have direct contact with infected birds. Its symptoms may include conjunctivitis and/or upper respiratory symptoms. On the other hand at least three H9 infections have been confirmed in humans.