Airborne Transmission: Transmission of contaminated particles or droplets through the air. In this way, birds spread the flu to each other just like humans spread
seasonal human flu to others.
Direct Contact: Direct contact with contaminated manure, feathers, or contaminated secretions from the respiratory tract, such as saliva. Healthy birds, if not culled, should be far away from contaminated manure and secretions from infected birds. Boots worn by those working with poultry should be
disinfected before and after contact with poultry.
Contaminated Eggs: Broken contaminated eggs infecting healthy individuals. Contaminated eggs or those suspected of being contaminated should be eliminated and kept far away from healthy birds that will not be culled. Eggs and egg shells should not be fed back to healthy birds.
Movement of Infected Birds: Movement of sick birds, or already infected birds, from one flock to another. New birds should be put in quarantine before joining the rest of the flock. See the USDA's
Biosecurity for the Birds for tips on how to keep your poultry healthy.
Contaminated Equipment, Vehicles and Clothing: Contact with contaminated equipment such as vehicles used to transport poultry, clothing and shoes, and egg cartons. Virus can lounge around on surfaces for days, and in water, sometimes for a month or more.
Disinfect equipment, or simply avoid sharing equipment between flocks and change clothing before working with the flock.
Wild Birds and Waterfowl: Contact with infected wild birds and waterfowl could spread bird flu among domestic birds. However, transmission among domestic birds is still the biggest threat. Some waterfowl may harbor the H5N1 virus, and other bird flu viruses, without getting sick themselves.
Contaminated Drinking Water: Contamination of drinking water with contaminated bird feces. Bird feces are loaded with virus and the virus can survive in feces for several days. Virus can remain alive in cool water for more than a month.
Garbage Flies: As their name implies, these flies like to lay eggs in decaying meat and feces. They can spread disease, such as bird flu, simply by moving virus from one surface to another, for example, from feces to food.
Overview of Bird to Bird Transmission of Avian Flu: Birds are the primary target of avian influenza viruses, or bird flus. There are several types of bird flu viruses, not just
H5N1. Bird to bird transmission of these viruses can be very efficient and therefore rapid.
Avian influenza viruses are transmitted in the same way regardless of their subtype and can be considered to be highly pathogenic (HPAI) or lowly pathogenic (LPAI). Some of the issues being investigated are how bird flu is transmitted among birds and if wild birds play a significant role in its spread. Until now, low pathogenic bird flu (also known as LPAI) was thought to have origins in wild birds who normally would not die from the disease.
Highly pathogenic bird flu (also known as HPAI) is more common in domestic poultry because the virus changes somewhat with each new bird it infects. Since domestic poultry in commercial operations live in crowded conditions, the virus makes many jumps from bird to bird, and therefore can change very quickly into a highly virulent strain of the bird flu virus. The virus can also evolve into a bird flu strain that is less virulent. See why I think backyard birds in developed countries are not likely to be the main culprits in spreading bird flu.
If we look at life from the virus' point of view, it is advantageous to become more virulent and have the ability to infect more individuals. Being more virulent results in the production of more virus and gives the virus more opportunities to change and even possibly reassort with other viruses in order to infect other species.
