Virus | Subtypes | Mutation | Spread

Origins of Bird Flu Outbreaks

Outbreaks of avian influenza in domestic poultry generally originate from contact with wild birds or their excretions. Waterfowl in particular, are believed to be the major source of bird flu viruses from the wild. Wild ducks, seagulls and other shore birds are capable of carrying viruses without becoming ill and they are believed to have done so for centuries. The viruses settle and replicate in the intestines of each bird and are distributed through their feces to cause contagion in other birds.

Bird Flu Infection in Domestic Poultry

Domestic flock often contract bird flu viruses from wild bird species due to one of the following two reasons:

• Free-range birds may come into direct contact with wild infected birds or their faeces or;
• Domestic poultry may share a common water source with wild birds, whereby the water may become contaminated from waterfowl excretions.

Once the virus successfully infects a flock, equipment and staff traveling in between farms and flocks then continues the chain reaction, which can subsequently spread over a vast region.



Air-borne transmission is also possible between birds within a close range and garbage flies have been believed to be a contaminating agent in the past. Infected eggs that are broken and spilt will carry virus particles as well and are another virus source when left exposed to other birds.

Bird flu viruses are considered highly infectious and it's believed that just 1 gram of infected faeces would hold the necessary amount of highly pathogenic virus particles to infect around one million birds. In particular, ducks have been known to release viruses in their excretions for over 30 days, making infected ducks dangerous transmitters of the disease.

Currently Infected Countries

The following map details countries which are currently affected by the H5N1 strain chiefly common to Southeast Asia: