Influenza, commonly called "the flu", is a contagious disease caused by viruses that infect the respiratory tract including nose, throat, and lungs. Many varieties of influenza viruses exist. Some viruses infect only humans, others only birds, pigs or dogs. Some can infect more than one mammal (called "cross species"). In birds, this disease is called avian influenza or the "bird flu".
Avian influenza has been around for over 100 years. It was first reported as "fowl plague" in 1878 when it caused a lot of deaths in chickens in Italy.
Avian flu can affect the respiratory, gastro-intestinal, reproductive or nervous system (or combinations of these) in many kinds of birds. The earliest signs of infection in chickens are a loss of appetite and a decrease in egg production. Symptoms of avian flu can range widely from mild illness to a highly infectious disease that can kill an entire flock of chickens within hours. Some wild birds and waterfowl (like ducks and geese) can carry the virus without showing signs of infection. Pigeons appear resistant to the infection. However, domestic chickens are very susceptible to influenza infections which can easily spread to other chickens and quickly turn into epidemics (in poultry).
NOTE: For information about the common flu in humans, please see the OSH Answers Influenza.
Avian influenza is mainly spread by direct contact between infected birds and healthy birds. It can also be transmitted when birds come in contact with equipment or materials (including water and feed) that have been contaminated with feces or secretions from the nose or mouth of infected birds.
People can also spread the disease indirectly from farm to farm by their carrying the virus on their clothing, boots or vehicle wheels.
Wild birds normally can carry the virus without getting ill themselves. However, there have been a few rare situations where wild flocks became ill or where migratory birds infected local poultry flocks along their flight routes. Scientists are currently studying how and why this change is happening.
No. Avian influenza viruses can be classified as low pathogenic avian influenza viruses (LPAI) and high pathogenic avian influenza viruses (HPAI). "Low pathogenic" means that the virus causes a mild disease like ruffled feathers and decreased egg production. High pathogenic viruses are extremely contagious and can cause up to 100% of an infected flock to die.
Type A influenza viruses (Influenzavirus A) cause avian influenza.
Yes. The influenza virus belongs to the family of orthomyxoviruses which has influenza types A, B, and C.
Only influenza type A viruses cause flu in birds. Influenza type A viruses have been found in wild and domestic birds from around the world. The majority of viruses have been found in waterfowl (e.g., ducks, geese, gulls, and terns) and domestic birds (e.g., chickens, turkeys, ducks, geese, pheasants and quail). There are many distinct varieties or strains of avian influenza type A viruses but most strains in ducks and other birds do not cause any disease symptoms.
Influenza type A viruses can also infect people, pigs, hogs, dogs, horses, seals, whales, and mink.
Influenza types B viruses are usually only found in humans. Influenza type B viruses can cause human epidemics but they have not caused pandemics.
Influenza type C viruses cause mild symptoms in humans and do not cause epidemics or pandemics. Type C viruses have also been found in pigs and dogs.
Influenza type A viruses are classified into subtypes and each subtype is further divided into strains.
The H and N letters refer to the different kinds of proteins found on the outside surface of the influenza virus. The various subtypes of type A influenza virus depend on the kinds of proteins that stick out from the surface of the virus - the haemagglutinin or HA protein and the neuraminidase or the NA protein. The body's immune system can make antibodies that can recognize these specific virus proteins (antigens) and therefore fight that specific influenza virus.
Researchers have found 16 kinds of HA proteins and 9 NA proteins in many combinations in bird flu viruses. These combinations are reported as strains of the influenza virus H(number) N(number). For example: H7N1, H9N2, H5N1, etc.
Avian influenza viruses do not usually infect people, but there have been over 140 cases between 2004 and early 2006. Currently, most cases of infection in people are believed to be the result of direct contact with infected poultry or contaminated surfaces.
Among all the avian influenza viruses that have caused illness in people, the subtype H5N1 has been associated with very serious illnesses and death. As reported by the Center for Disease Control and Prevention, in most outbreaks, more than half of those infected with the virus have died. Most cases have been in children or young adults who were previously healthy. Because these viruses do not normally infect humans, we do not have a natural immunity to it.
Health authorities are concerned for 2 main reasons. First, most people have not been exposed to an H5N1 virus. If a human version of this virus develops, everyone will be susceptible to infection. No one will have immunity, and the virus will be able to spread rapidly.
Secondly, the H5N1 avian strain is highly pathogenic (easily causes disease). The rate of serious illnesses and death could be very high.
While rare, disease specialists believe that avian influenza in humans is mainly caused by contact with:
Currently, the virus does not spread easily from birds to humans, or from human to human. However, there have been very rare cases when the avian virus has spread from one ill person to another, but the transmission has not been observed to go beyond one person.
Because all influenza viruses have the ability to change, this current virus may eventually gain the ability to spread between people easily.
The symptoms are similar to those of 'regular' human influenza and can include fever, cough, aching muscles, sore throat, eye infections and serious respiratory infections including pneumonia.
At present, there is no vaccine against this new strain of avian influenza. Some studies indicate that certain drugs that fight human influenza may help prevent serious illness among people infected with the avian influenza virus.
No. Avian influenza is not spread by cooked food. While the World Health Organization recommends proper cooking as a good general practice, it is even more important in countries that have a current outbreak of avian influenza. For example, the H5N1 virus will be killed by heat so foods should be cooked to a temperature of 70°C to make sure they are safe to eat (no pink parts). Eggs should also be thoroughly cooked (no runny yokes).
Food preparation techniques are also important. Be sure that juices from raw poultry or poultry products do not touch or mix with other foods that will be eaten raw. Always wash your hands thoroughly and wash surfaces after touching poultry products. Cleaning with soap and water is appropriate.
Many scientists believe it is only a matter of time until the next influenza pandemic occurs. The human cases of avian flu are being monitored and studied closely as they may be a "warning sign".
Traditionally, an influenza pandemic occurs when a new influenza A virus appears. Whether the next pandemic is actually caused by the current avian influenza A viruses is not certain, but in general, disease specialists note that we are "overdue" for a flu pandemic of some origin. The World Health Organization considers the risk of a pandemic as "serious".
The most important step you can take to reduce the chance of infection is to wash your hands regularly - always wash regularly with soap and warm water.
See the OSH Answers Hand Washing - Reducing the Risk of Common Infections for more details.
Other steps you can take for personal hygiene are listed in Good Hygiene Practices - Reducing the Spread of Infections and Viruses.
The Public Health Agency of Canada together with other federal government departments and provincial and territorial governments continue to take several actions to protect Canadians.
One of these actions includes maintaining the Canadian Pandemic Influenza Plan. The plan maps out how Canada will prepare for and respond to pandemic influenza. For example, the infection prevention and control section addresses occupational health issues relating to health care workers. It also contains sections for the general public. Some of the issues addressed include: hand hygiene, the use of personal protective equipment as well as temporary closure of schools, day cares and "non-essential" businesses.
The Public Health Agency's websites are:
The Government of Canada's website is:
For more information and more references to places for the latest information about the pandemic flu, please also see the OSH Answers document on Pandemic Influenza.
Document last updated on April 5, 2006