Direct Contact with Infected Birds: Almost everyone who has been infected with the H5N1 subtype of bird flu have had direct contact with birds or their derivatives. Of the confirmed cases of H5N1 infection in humans reported to the World Health Organization (WHO), less than half a dozen of them have been blamed on human to human transmission.
Ingestion, Inhalation and Contact with Bird Faeces: The accidental ingestion, inhalation and other contact with bird faeces is one mode of transmission of bird flu. Bird faeces from infected birds are loaded with live virus and wet faeces can harbor the virus for days, depending on various factors including the type of virus and the temperature of the surroundings. Touching birds or surfaces with bird faeces and then touching your eyes, nose or mouth is one way of accidentally infecting yourself. Faeces may spread through the air as well.
Killing, Cleaning, Plucking Feathers or Disposing of Dead Birds: Many people who have been infected with the virus were involved in either the killing of birds, cleaning carcasses, feather plucking or disposing of dead birds. Farmers, poultry butchers handling raw meat and salespeople selling raw poultry have been affected. Children playing around infected poultry have been infected with the virus as well.
It is thought that plucking feathers causes the the virus to go airborne.
Contaminated Water: H5N1 virus remains alive in water for several days, even up to a month or longer in cooler waters (and perhaps even longer at refrigerator temperatures). Wild birds, such as ducks, excrete large amounts of H5N1 virus in their faeces even when they show no signs of being ill. Public drinking water from bodies of water could become contaminated.
There's still no known mechanism for contracting bird flu via the gastrointestinal tract, meaning no one knows if you can really get bird flu by eating or drinking the virus. However, the possibility exists and hasn't been discarded.
Contaminated Sewage: There is not any evidence that humans have been infected by bird flu through sewage, but there is potential for infection via this route. Faeces from infected humans contain H5N1 virus. H5N1 remains alive and well in wet faeces and water for several days depending on various factors such as the temperature of the environment. Sewage used for the irrigation of crops or dumped into bodies or water that are then used for bathing or drinking water are some modes of human contact with sewage.
Feathers: The US has restricted entry of untreated bird feathers from countries where bird flu outbreaks have been reported in poultry. Feathers can harbor bird flu virus. Feathers and some other bird products can undergo processes that make them virus free and these can be imported with special permits. The USDA Animal and Plant Health Inspection Service has published a [link url=http://www.aphis.usda.gov/vs/ncie/country.html#HPAI]list of countries affected by Highly Pathogenic Avian Influenza H5N1[/link).
Consumption of Improperly Cooked Infected Poultry Products: Properly cooked poultry meat, blood and eggs pose no human health risk. Follow Tips to Cooking Poultry Safely. Meat should be cooked to at least 165 F (70 C) inside and out and should not be pink after cooking. Fresh blood from poultry should not be drank or eaten. Eggs should be cooked thoroughly, no runny yolks. Although the USDA carefully inspects chickens and meat and the possibility of infected poultry entering the market is low, properly cooked poultry prevents foodborne illness.
There is no known mechanism of people contracting any kind of influenza virus from eating it.
Wild Birds: Thought to be the natural reservoir for bird flu, wild birds are implicated in the spreading of bird flu to domestic poultry. So far there is no evidence of human infection of bird flu through direct contact with wild birds. The risk of contracting bird flu through bird feeders is low, in fact, no such infection has been reported. In addition, water birds, not perching birds (Passeriformes) are the prime reservoir for bird flu.
In most of the cases of wild birds found with bird flu, it is thought that the wild birds contracted bird flu from neighboring poultry operations.
Sources:
- World Health Organization. Review of latest available evidence of risk to human health through potential transmission of avian influenza (H5N1) through water and sewage. Last updated March 24, 2006. See text: http://www.who.int/water_sanitation_health/emerging/h5n1background.pdf
- World Health Organization. Avian Influenza, Assessing the Pandemic Threat. January, 2005. See text: http://www.who.int/csr/disease/influenza/H5N1-9reduit.pdf
- United States Department of Agriculture. Avian Influenza Factsheet. Release 0092.06. United States Prepares for Highly Pathogenic (H5N1) Avian Influenza in Wild Birds. Last modified March 20, 2006.
- United States PandemicFlu.gov. Questions and Answers about Wild Birds.
- United States Department of Agriculture. Animal and Plant Health Inspection Service. List of Countries Affected by Highly Pathogenic Avian Influenza Subtype H5N1..