How virus is spread
Infected birds excrete avian flu virus in their saliva, nasal secretions, and feces, and can also have viruses on their feathers. Other birds can get the avian flu by having contact with these excretions, having contact with a surface contaminated with virus, or having contact with an infected bird.
The avian flu virus can survive outside the host for about 48 hours, or more if it is contained in feces.
Migratory waterfowl (especially wild ducks) are the natural hosts of avian flu viruses, and are able to harbor avian flu viruses without getting sick. The virus thrives in the birds’ intestines, so infected birds’ feces contains viruses.
As the waterfowl migrate, they can spread the virus, introducing the virus into new areas, sometimes in poultry farms. The waterfowl usually infect other birds by direct contact, by their feces (which contains viruses), or by contaminating the water used by the birds.
Once one chicken in a poultry farm has been infected, it is easy for avian flu to spread throughout the entire flock. The chickens are in close proximity to each other, so transmission of the disease is almost certain. Chickens usually get infected from other sick chickens on the farm by direct contact, or by contaminated equipment.
Avian flu can even spread to other farms, when feces (containing viruses) is accidentally transferred between farms, and when equipment and vehicles contaminated by infected chickens are used at other farms.
Avian flu can also spread to new areas in a live bird market. A live bird market provides opportunity for avian flu viruses to infect new hosts.