Chapter IV. Spread of Avian Influenza Viruses among Birds

Avian Influenza Outbreaks in Poultry

Domesticated birds may become infected with avian influenza virus through direct contact with infected waterfowl or other infected poultry, or through contact with surfaces (such as dirt or cages) or materials (such as water or feed) that have been contaminated with virus. People, vehicles, and other inanimate objects such as cages can be vectors for the spread of influenza virus from one farm to another. When this happens, avian influenza outbreaks can occur among poultry.

Avian influenza outbreaks among poultry occur worldwide from time to time. Since 1997, for example, more than 16 outbreaks of H5 and H7 influenza have occurred among poultry in the United States. The U.S. Department of Agriculture monitors these outbreaks.

Low pathogenic forms of avian influenza viruses are responsible for most avian influenza outbreaks in poultry. Such outbreaks usually result in either no illness or mild illness (e.g., chickens producing fewer or no eggs), or low levels of mortality.

When highly pathogenic influenza H5 or H7 viruses cause outbreaks, between 90% and 100% of poultry can die from infection. Animal health officials carefully monitor avian influenza outbreaks in domestic birds for several reasons:

• the potential for low pathogenic H5 and H7 viruses to evolve into highly pathogenic forms
• the potential for rapid spread and significant illness and death among poultry during outbreaks of highly pathogenic avian influenza
• the economic impact and trade restrictions from a highly pathogenic avian influenza outbreak.
• the possibility that avian influenza could be transmitted to humans

When avian influenza outbreaks occur in poultry, quarantine and depopulation (or culling) and surveillance around affected flocks is the preferred control and eradication option.

Avian Flu in Birds is Spreading in Asia and Other Countries

• Avian influenza - commonly called "bird flu" - is an infection caused by influenza viruses that occur naturally in birds.
• Wild birds can carry the viruses, but usually do not get sick from them. However, some domesticated birds, including chickens, ducks, and turkeys, can become infected, often fatally
• One strain of avian influenza, the H5N1 virus, is endemic in much of Asia and has recently spread into Europe. Avian H5N1 infections have recently killed poultry and other birds in a number of countries.
• Strains of avian H5N1 influenza may infect various types of animals, including wild birds, pigs, and tigers.
• Symptoms in birds and other animals vary, but virulent strains can cause death within a few days