Avian influenza is a contagious viral infection that can affect all species of birds. On rare occasions, it can cause disease in humans with symptoms that are similar to other types of flu - fever, malaise, sore throats and coughs. Avian flu has a high fatality rate in humans.
What is avian influenza?
Avian influenza is a contagious viral infection that can affect all species of birds (chickens, turkeys, guinea fowl, pet birds and wild birds). In intensive poultry rearing systems, young fattening turkeys and laying hens are usually the most affected species.
Wild birds may carry influenza viruses without becoming ill due to natural resistance. Wild waterfowl present a natural reservoir for these viruses and can be responsible for the primary introduction of infection into domestic poultry. Signs of the disease range from a mild infection with no symptoms to a severe epidemic that kills up to 100 percent of infected birds.
Several virus types exist -- the strain that causes the greatest number of deaths is called highly pathogenic avian influenza. Low pathogenic strains of avian influenza have the potential to rapidly become highly pathogenic and some countries have adopted an eradication policy for low pathogenic strains of avian influenza due to that risk.
How is the disease transmitted?
Infection most commonly results from:
- contact with wild birds, especially waterfowl which may transmit the disease yet show no symptoms;
- contact with infected poultry and poultry products;
- contaminated clothing and footwear;
- contaminated vehicles and equipment;
- contaminated feed and water;
- high concentrations of virus in manure and litter;
- insects can act as carriers of the disease;
- rodents or farm dogs and cats which may act as mechanical vectors.
Does avian influenza occur in Canada?
Highly pathogenic avian influenza was isolated in Ontario in 1966, the only occurrence for Canada. Low pathogenic avian influenza has been isolated in Canada three times since 1975.
What is being done to prevent its introduction?
The Canadian Food Inspection Agency imposes strict regulations on our imports of poultry and poultry products from foreign countries. At ports of entry, poultry vehicles and equipment may be inspected and disinfected if needed to ensure that they are free from the disease.
Should an outbreak of the disease occur, the Canadian Food Inspection Agency has developed an emergency response strategy which includes a stamping out policy. To limit the spread of the disease, a "control area" would be declared to contain all infected flocks. Producers would receive compensation for infected flocks ordered destroyed. Movement of poultry, poultry products, people and vehicles on or off infected farms would be restricted. Poultry and eggs at local markets would be tested for the presence of antibodies.
Avian influenza is divided into subgroups of viruses which change their genetic make-up readily. New types of viruses are often generated from two or more existing strains. Because of this continuous change, it is less feasible to produce vaccines in advance of a disease outbreak.
What can travellers do to avoid bringing the disease into the country?
Through its Travel Medicine Program, Health Canada is providing regular updates and travel guidance to Canadians at home and abroad. For information on the most up to date advice, please visit www.TravelHealth.gc.ca.
Travellers from abroad may carry the disease on their clothing including footwear and in poultry products. When travelling:
- Declare all poultry products you wish to bring into Canada;
- If you visit a farm while abroad, make sure that clothing and footwear you wear on the farm are free from soil and manure before entering Canada. Launder clothing, clean and disinfect footwear after arrival;
- Don't visit areas where highly pathogenic avian influenza is known to occur.
What can livestock producers do to prevent infection on their farm?
The reservoir of infection is in the wild bird populations. It is essential for commercial poultry producers to maintain strict biosecurity to reduce the chances of introduction. On a farm:
- Keep away from areas frequented by wild fowl;
- Keep strict control over access to your poultry houses by people and equipment;
- Ensure that reusable equipment is cleaned and disinfected before you take it into poultry houses;
- Discourage wild birds from visiting your farm; do not have bird feeders and duck ponds;
- Maintain high sanitation standards.
If symptoms are noticed or suspected in poultry, contact your veterinarian or the Canadian Food Inspection Agency in your area. Producers are obligated to report this disease under the Health of Animals Act in order to protect Canada's poultry industry.
Is avian influenza transmissible to humans?
Influenza viruses of avian origin may on rare occasions cause disease in humans. The exact mode of transmission from birds to humans is not known. Human to human transmission of avian influenza is thought to be extremely limited.
How did the current outbreak spread to humans?
There is currently no evidence of human-to-human transmission. The current H5N1 strain has been partially sequenced and all of its genes are avian in origin, suggesting that the virus has not acquired any human genes. The acquisition of human genes increases the likelihood that a virus of avian origin can be readily transmitted from one human to another. World Health Organization (WHO) investigations are currently focussing on the source of infection.
Avian influenza viruses do not normally infect species other than birds and pigs. Here are some examples of previous outbreaks. The first documented infection of humans with an avian influenza virus occurred in Hong Kong in 1997, when the H5N1 strain caused severe respiratory disease in 18 humans, leading to 6 deaths. The infection of humans coincided with an epidemic of highly pathogenic avian influenza, caused by the same strain, in Hong Kong's poultry population.
Extensive investigation of that outbreak determined that close contact with live infected poultry was the source of human infection. Studies further determined that the virus had jumped directly from birds to humans. This was the first time that an avian influenza virus was transmitted directly to humans. A second outbreak of H5N1 avian influenza in Hong Kong in February 2003 caused 2 cases and 1 death.
How can bird flu cause a pandemic?
Avian flu outbreaks in birds increase opportunities for human exposure. Increases in the number of infections in humans increase opportunities for the avian and human strains to exchange genetic material. If a new virus subtype emerges as a result of this “mixing,” and if that virus proves capable of spreading easily and sustainably from person to person, then the outbreak of avian flu has created the conditions for the start of an influenza pandemic.
What is antigenic shift?
Flu viruses are constantly changing and evolving, which is why Health Canada continually monitors both the domestic and global flu situation. Influenza A viruses in particular can change radically. The virus, including subtypes from different species like the bird flu, can swap genetic materials and merge. This process is known as antigenic shift and creates a new flu virus different from both its parent viruses.
Since the virus is completely new, we have no immunity to it and existing vaccines cannot protect us against it. For this to happen, the new flu virus needs to have genes from human influenza viruses that make it readily transmissible from person to person for a sustainable period.
Conditions that favour the emergence of antigenic shift have long been thought to involve humans living in close proximity to domestic poultry and pigs. Because pigs are susceptible to infection with both avian and mammalian viruses, including human strains, they can serve as a “mixing vessel” for the scrambling of genetic material from human and avian viruses, resulting in the emergence of a new subtype against which the population has no immunity.
What can be done to stop the spread of avian influenza?
The WHO has alerted countries about the need to intensify surveillance for animal infections. Culling of infected or potentially exposed poultry flocks is a standard control measure and has been effective in stopping past epidemics of avian influenza in several countries.
Vaccination of persons at high risk of exposure to infected poultry, using existing vaccines effective against currently circulating human influenza strains, can reduce the likelihood of co-infection with human and avian influenza strains, reducing the risk that genes will be exchanged.
What about a vaccine? Aren't flu vaccines made in eggs? How can you make the vaccine if birds are infected with the disease?
It is not feasible to stockpile a flu vaccine for a pandemic outbreak of influenza. In a pandemic, the flu virus is one that has changed radically. Manufacturing can't begin until the new virus has emerged and the vaccine strain is available.
Even with the best science available to us, it will take at least four to six months for manufacturers to make a new vaccine once we have obtained the new virus. Health Canada has taken steps to be able to ramp up production once the virus is available. In this event, production of influenza vaccine by a domestic manufacturer, Shire Biologics of Saint-Foy, Que., can start immediately and production capacity can be increased. The goal is to produce enough vaccine to protect all Canadians as quickly as possible. Canada is the first country worldwide to plan for a secure vaccine supply through the contracting of a domestic supplier. The contract ensures that everything required for vaccine production, including the egg supply and storage facilities, is in place.
During the 2003 outbreak of avian influenza in Hong Kong, the WHO network took approximately 17 days to develop the new H5N1 vaccine that could grown in eggs by using a new technique called reverse genetics. The WHO is comparing this H5N1 vaccine to the H5N1 virus isolated from the current outbreaks to determine if this vaccine would be effective against the current strain or if a new one would need to be developed. Based on last year's experience, it is possible a new vaccine that would grow in eggs could be made available to manufacturers within the same time frame. After a new vaccine strain is identified, there are still many steps that has to be taken in the manufacturing, testing and licensing processes before a safe vaccine can be administered.
As a precautionary measure, the WHO is moving forward with the procedures needed to rapidly produce a new influenza vaccine capable of protecting humans against the H5N1 strain of avian influenza. Prototype viruses for vaccine production are being prepared by laboratories in the WHO Global Influenza Network. Several laboratories in this network have the high-security (biosafety level 3) facilities needed to safely conduct work on a highly pathogenic virus such as H5N1. Prototype viruses are then supplied to manufacturers as the “seed stock” for vaccine production.
Does Canada have a biosafety level 3 facility?
Yes. Canada has a number of biosafety level 3 facilities and a level 4 facility at the National Microbiology Lab in Winnipeg.
What is reverse genetics?
Reverse genetics merges selected genetic information of the virus taken from actual cases with a laboratory virus. The resulting virus is recognized by the human immune system, and causes a protective immune response, but no disease. The virus can also be genetically modified so that it is no longer lethal to chicken embryos. As a further advantage, use of the reverse genetics technique produces a prototype virus with predictable growth during vaccine production.
Is it safe to eat poultry?
Yes, it is safe to eat poultry. As a precaution and until further information is available, however, Health Canada is advising travellers to affected areas that they should not consume undercooked poultry, raw eggs or lightly cooked egg products (such as runny eggs) and that they avoid unnecessary contact with live poultry. This includes markets where live birds are sold, as it is possible for the avian influenza virus to stick to hair and clothing and may be inhaled.
Eating poultry in Canada is perfectly safe. The Canadian Food Inspection Agency (CFIA) has import restrictions in place on poultry and non-processed poultry products from any of the affected countries due to existing disease concerns. These countries are all considered to be high-risk for exotic Newcastle disease, another serious viral disease that will affect poultry. There are no known cases or outbreaks of highly pathogenic avian influenza (HPAI) in Canadian poultry. Canada has never reported a single case of HPAI.
The CFIA continues to monitor the outbreak situation in Asia, and will maintain the existing import restrictions until any of the affected countries are deemed free with respect to the spread of all avian diseases of concern.
Canada also has in place import restrictions for swine from the same countries because these countries are not recognized by the CFIA as countries free of serious swine diseases.
What can you do to protect yourself and your family?
It is important to remember that there are no cases of human to human transmission of avian influenza. Prevention is the best defence against influenza. Canadians should protect themselves and each other by:
- Getting a flu shot;
- Washing their hands frequently; and
- Staying home if they are sick.
Since the SARS outbreak in March 2003, Health Canada, in consultation with P/T public health officials and other national and international experts, has taken steps in the following areas to strengthen its capacity to respond to future infectious disease outbreaks:
- disease surveillance;
- infection control
- laboratories;
- partnering and collaboration; and
- emergency preparedness.
For example, Health Canada is providing specific guidelines on overall public health management of cases of SARS and other severe respiratory illness where investigation or follow-up in the community is required.