Where is the disease found?

AI occurs worldwide and different strains are more prevalent in certain areas of the world than others.

Of particular interest are outbreaks of highly pathogenic H5N1 AI that began in south-east Asia in late 2003. Over the past years, several other Asian countries have reported outbreaks and in some, the disease is now considered to be endemic (always present). Outbreaks of HPAI H5N1 have also been reported in Africa and Europe.

How is the disease transmitted and spread?

Several factors can contribute to the spread of AI viruses including globalization and international trade (legally and illegally), marketing practices (live bird markets), farming practices and the presence of the viruses in wild birds.

Wild birds normally can carry avian influenza viruses in their respiratory or intestinal tracts and usually do not get sick. Wild birds have historically been known as reservoirs for AI viruses, mostly of low pathogenicity. Around the world, surveillance measures have been put in place to monitor occurrence and characteristics of AI viruses in wild birds. In wild birds, it is common during routine testing to find some influenza viruses. The vast majority of these viruses do not cause disease.

In studying current HPAI H5N1 outbreaks, the exact role of wild birds in spreading the virus over long distances is still not fully understood in all situations. Generally, there are many uncertainties about the wild species involved, the migratory routes used and, above all, the possibility that some species could become permanent reservoirs of the H5N1 virus, with carriers showing no clinical signs of the disease. AI viruses can be spread through ddirect contact with secretions from infected birds, especially faeces or through contaminated feed, water, equipment and clothing.

Apart from being highly contagious among poultry, avian influenza viruses are readily transmitted from farm to farm by the movement of domestic live birds, people (especially when shoes and other clothing are contaminated), and contaminated vehicles, equipment, feed, and cages. Highly pathogenic viruses can survive for long periods in the environment, especially when temperatures are low. For example, the highly pathogenic H5N1 virus can survive in bird faeces for at least 35 days at low temperature (4oC). At a much higher temperature (37oC), H5N1 viruses have been shown to survive, in faecal samples,for six days.

Other species including cats and pigs can exceptionally become infected with the HPAI H5N1 virus. Infections of pigs are of concern because the species is susceptible to infections of both avian and human influenza viruses and this may provide the H5N1 AI virus the opportunity to reassort or mutate. While sporadic infection with HPAI H5N1 virus in both species have been reported over the past three years there is no scientific evidence to suggest that either species plays a significant role in the epidemiology of the disease or as a source of virus to other species.

source: http://www.oie.int/eng/en_index.htm