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Overview

Bird flu is an infection caused by avian flu viruses. These viruses occur naturally among birds. Wild birds worldwide carry the viruses in their intestines, but usually do not get sick from them. However, bird flu is very contagious among birds and can make some domesticated birds, including chickens, ducks, and turkeys, very sick and kill them. Bird flu viruses do not usually infect humans, but a growing number of cases of human infection with bird flu viruses have occurred since 1997.

So far, avian flu from person to person has been rare and spread has not continued beyond one person. However, because all influenza viruses have the ability to change, scientists are concerned that this virus could one day be able to infect humans and spread easily from one person to another. Because these viruses do not commonly infect humans, there is little or no immune protection against them in the human population. If the virus were able to infect people and spread easily from person to person, an influenza pandemic or worldwide outbreak of disease could begin. No one can predict when a pandemic might occur.

If H5N1, or any other strain of avian influenza, were to evolve into a pandemic strain of influenza, scientific research suggests that we would see efficient and sustained human-to-human transmission of the virus. This means we would see a large and growing number of new and unrelated cases increasing daily which, to date, has not been the case.

Causes

Influenza A (H5N1) virus - also called "H5N1 virus" - is an influenza A virus subtype that occurs mainly in birds. It was first isolated from birds in South Africa in 1961. Like all bird flu viruses, H5N1 virus circulates among birds worldwide, is very contagious among birds, and can be deadly.

Infected birds shed flu virus in their saliva, nasal secretions, and feces. Susceptible birds become infected when they have contact with contaminated excretions or surfaces that are contaminated with excretions. It is believed that to date most cases of bird flu infection in humans have resulted from contact with infected poultry or contaminated surfaces.

Symptoms

Symptoms of bird flu in humans have ranged from typical flu-like symptoms (fever, cough, sore throat and muscle aches) to eye infections, pneumonia, severe respiratory diseases (such as acute respiratory distress), and other severe and life-threatening complications. The symptoms of bird flu may depend on which virus caused the infection.

Treatment

The risk from bird flu is generally low to most people because the viruses occur mainly among birds and do not usually infect humans. However, during an outbreak of bird flu among poultry (domesticated chicken, ducks, turkeys), there is a possible risk to people who have contact with infected birds or surfaces that have been contaminated with excretions from infected birds. The current outbreak of avian influenza A (H5N1) among poultry in Asia and elsewhere is an example of a bird flu outbreak that has caused human infections and deaths. In such situations, people should avoid contact with infected birds or contaminated surfaces, and should be careful when handling and cooking poultry. For more information about avian influenza and food safety issues, visit the World Health Organization website.

Studies suggest that the prescription medicines approved for human flu viruses would work in preventing bird flu infection in humans. However, flu viruses can become resistant to these drugs, so these medications may not always work.

The H5N1 virus currently infecting birds that has caused human illness and death is resistant to amantadine and rimantadine, two antiviral medications commonly used for influenza. Two other antiviral medications, oseltamavir and zanamavir, would probably work to treat flu caused by the H5N1 virus, though studies still need to be done to prove that they work.

A vaccine is not currently available. At this point though, a genetically modified seed strain for H5N1 vaccine development is available and vaccine manufacturers in several countries, including Canada have acquired this seed strain. Manufacturers are working now to optimize the conditions under which the modified H5N1 virus grows in eggs. This will allow them to develop a virus seed bank for future vaccine production.

The current season flu shot does not protect against avian influenza. Immunization with the current season flu vaccine would be important though for those in close contact with infected poultry because it could reduce the likelihood that a worker would be infected with the human and avian forms of influenza at the same time. If a person were infected with both viruses at the same time, there is a possibility that the two viruses will "mix" and create a new virus against which people have no immunity.