Language selection

Government of Canada / Gouvernement du Canada

Search

Avian influenza A(H5N1): For health professionals

Current situation

Outbreaks of avian influenza A(H5N1) continue to occur in Canada and globally. The risk of avian influenza infection to most people in Canada remains low.

On this page

Key information

Avian influenza A(H5N1) is a subtype of avian influenza virus that mainly infects birds, but has been identified in other animals and has caused rare and sporadic infections in humans.

Outbreaks of avian influenza A(H5N1) in domestic and wild birds and some mammals have recently emerged and become widespread in Europe and North America, including across Canada, as well as Central and South America, sub-Antarctic regions and Antarctica. Government authorities in Canada are currently responding to the outbreak of avian influenza A(H5N1) in farmed birds and wildlife across Canada.

Human cases of avian influenza A(H5N1) have primarily occurred due to zoonotic transmission through direct contact with infected birds (dead or alive) or contaminated environments. Recently, in the United States, a number of human cases have been linked to close contact with dairy cattle infected with avian influenza A(H5N1). Human-to-human transmission is rare and there has been no evidence of sustained transmission between humans.

The virus mainly affects the respiratory tract but can also cause gastrointestinal or central nervous system manifestations. Infection may progress to severe illness and can be fatal.

Clinicians and front-line laboratory personnel are encouraged to follow the Protocol for Microbiological Investigations of Severe Acute Respiratory Infections to facilitate the diagnosis of severe respiratory infection caused by pathogens with epidemic potential.

Protocol for Microbiological Investigations of Severe Acute Respiratory Infections

Antivirals used to treat influenza can be effective in reducing morbidity and mortality, especially if administered early in the course of illness (ideally within 48 hours). Prophylactic use of influenza-specific antivirals (pre and post exposure) may prevent illness.

Human infections of avian influenza A(H5N1) are notifiable under the International Health Regulations (2005). Provincial and territorial public health authorities are required to report confirmed and probable human cases of avian influenza A(H5N1), irrespective of illness symptoms or severity, to the Public Health Agency of Canada (PHAC) within 24 hours of their own notification, as per the Emerging Respiratory Pathogens and Severe Acute Respiratory Infection Case Report Form.

Emerging respiratory pathogens and severe acute respiratory infection case report form

PHAC is required to report any human case detected in Canada to the World Health Organization according to the International Health Regulations (2005) requirements and timelines.

For detailed recommendations on public health management and reporting requirements, consult the appropriate local, provincial, or territorial health authorities.

Learn more:

Transmission

Agent of disease

Avian influenza A(H5N1) is a member of the Orthomyxoviridae family.

Influenza viruses are enveloped ribonucleic acid (RNA) viruses. Influenza virus strains can be classified according to their core proteins into:

Influenza D is seen in animals, predominantly cattle. It is not known to cause illness in humans.

Influenza A viruses can be further subdivided according to their antigenic surface glycoproteins: HA (hemagglutinin) and NA (neuraminidase).

Avian influenza A(H5N1) is classified as highly pathogenic avian influenza (HPAI), based on the severity of illness caused in birds.

Source of transmission

Transmission of avian influenza A(H5N1) to humans may occur in various ways and can be divided into 4 categories according to the source of infection.

Animal to human

Transmission of the virus occurs via inhalation or contact with mucus membranes (e.g., eyes, nose, mouth). Individuals can be exposed to the virus through contact with an infected animal's:

  • secretions (raw milk, mucus, saliva) or blood and feces
  • feathers

Transmission can occur during:

  • close contact with infected domestic (for example, farmed animals or pets) or wild animals
  • exposure to highly contaminated environments such as animal farms or live animal markets
  • exposure to environments where a person may have contact with the bodily fluids or feathers of infected animals, such as backyard or small flocks

Avian influenza A(H5N1) is not well adapted to mammals. However, there have been increasing reports of instances where non-human mammal-to-mammal (e.g., cattle, sea lions, cats) transmission may have occurred. Transmission from infected mammals to humans has also been reported.

Foodborne transmission

While the food in Canada is among the safest in the world, some raw foods and their juices can be contaminated by bacteria, viruses and parasites (foodborne pathogens) which can make people sick.

It is important to note that there is no evidence to suggest that the consumption of pasteurized dairy products, or fully cooked poultry, beef, game meat, organs or eggs can transmit the avian influenza A(H5N1) virus to humans. All evidence to date indicates that thorough cooking kills the virus.

Based on the limited research and information available, we do not know at this time if avian influenza A(H5N1) viruses can readily be transmitted through consumption of raw or undercooked animal products such as meat, eggs and milk. To date, there have been no confirmed cases of human infection with avian influenza A(H5N1) virus acquired through the consumption of food. However, as noted below, out of an abundance of caution and to prevent illness due to other pathogens, it is recommended that animal products should be thoroughly cooked, and dairy products should be pasteurized.

Traditional foods such as harvested wild bird eggs, wild geese and ducks, and other wildlife are important sources of food for many Canadians. Although the risk of being infected with avian influenza A(H5N1) is low for the general population, hunters, harvesters and other people who handle, prepare and cook wildlife may be at a higher risk.

Environmental exposures

The majority of avian influenza A(H5N1) human cases have occurred after contact with infected poultry. However, some cases have been associated with exposure to contaminated environments, such as live animal markets as well as dairy and poultry farms.

Theoretically, humans could get infected with avian influenza A(H5N1) by exposure to contaminated water (i.e., inhalation, ingestion, conjunctival or intranasal inoculation). However, the evidence to support this is limited. Environmental exposure through contaminated water (for example, bathing or swimming in household ponds, or lacking an indoor water source) has been suggested as a possible risk factor for human infection in a small number of avian influenza A(H5N1) studies.

Human to human

There is limited evidence from past outbreaks to suggest that there has been human-to-human transmission of avian influenza A(H5N1), for example, via close physical contact within a household. To date, sustained human-to-human transmission of avian influenza A(H5N1) has never been observed globally.

Learn more:

Signs and symptoms

The incubation period usually ranges from 1 to 5 days but can be up to 10 days.

Avian influenza A(H5N1) in humans mainly affects the respiratory tract. However, it can manifest with gastrointestinal or central nervous system symptoms.

The severity of signs and symptoms can range from mild to life-threatening depending on the clade, exposure, pre-existing medical conditions and clinical management.

The clinical manifestations of avian influenza A(H5N1) may include:

Serious complications may include:

Seroprevalence studies from endemic areas indicate that subclinical or mild infection may occur, with reports of seropositivity ranging from 0% up to 7% in people exposed to avian influenza A(H5N1), depending upon the region and occupational activities.

Based on available human case data since 2022, approximately 10% of reported A(H5N1) cases have resulted in death, which is lower than the pre-2022 fatality rate which was around 50%. However, there is still a limited number of global detections overall and these estimates may change as more detections are recorded. Respiratory failure is the most common cause of death.

Diagnosis

Most human cases have reported a history of exposure to dead or ill poultry. Clinicians and front-line laboratory personnel should consult their local public health unit and the Protocol for Microbiological Investigations of Severe Acute Respiratory Infections for guidance on appropriate testing, recommended procedures, and prioritization for avian influenza A(H5N1) investigations if exposure history has been established.

Protocol for Microbiological Investigations of Severe Acute Respiratory Infections

Laboratory testing

The primary method for detection of avian influenza A(H5N1) is reverse transcription polymerase chain reaction (RT-PCR) with subtyping (H5) for influenza A positive specimens. Positive and untypable influenza samples are sent to Canada's National Microbiology Laboratory for confirmatory testing.

Non-seasonal influenza A RT-PCR test

A non-seasonal influenza A RT-PCR test can be used to determine a probable case when an individual meets the exposure and/or illness criteria. If an exposed or ill person tests positive for influenza A and is negative for both A(H1) and A(H3) on a non-seasonal RT-PCR, it may indicate that they have avian influenza A(H5N1).

Influenza virus antigen test: Rapid influenza diagnostic test

This test should not be used to rule out influenza A infection. Suboptimal sensitivity of this test affects the ability to detect novel influenza viruses. While nasopharyngeal swabs are the primary specimen type for seasonal influenza viruses, past zoonotic influenza events suggest that nasopharyngeal swabs may not be sufficient. Multiple specimen types should be collected when both of these conditions are met:

Additional specimen collection types to be considered include:

Mishandled specimens from patients under investigation for avian influenza A(H5N1) are a serious risk to all, including health professionals collecting samples and laboratory personnel. For more on preventative measures before taking and accepting samples, refer to the section on infection prevention and control of transmission within a healthcare setting.

Infection prevention and control of transmission within a healthcare setting

Differential diagnosis

Diagnostic testing is required to confirm avian influenza A(H5N1) infection since other respiratory viral infections and respiratory bacterial infections may present with similar symptoms. Respiratory infections to consider on a differential diagnosis include:

Treatment

Antiviral agents can be used to treat suspected, probable, or confirmed avian influenza A(H5N1) cases. The ideal time to begin antiviral treatment is within the first 48 hours of symptom onset. Treatment can be initiated while awaiting confirmatory test results and should not be delayed.

Antiviral use should be guided by an individual risk assessment focusing on the exposure risk and the individual's risk factors for severe disease.

There are several antiviral options for the treatment of avian influenza A(H5N1):

Individual characteristics and case presentation should be considered when selecting the appropriate antiviral agent. Oseltamivir, zanamivir, and amantadine are available for use in Canada. Additional antivirals may be requested through Health Canada's special access programs and approved on a case-by-case basis.

Health Canada's special access programs: Request a drug

To date, there have been no clinical trials measuring the outcome of antiviral use in individuals infected with avian influenza A(H5N1). However, data from animal models and human observational studies have suggested a morbidity and mortality benefit with the use of oseltamivir as an antiviral agent.

Due to increased reports of antiviral resistance, amantadine is not recommended for use as a monotherapy for avian influenza. Emergence of oseltamivir resistance has also been reported. Combination therapy of antivirals with different mechanisms of action may be considered for select cases at risk of antiviral-resistant infection with monotherapy (e.g., immunocompromised individuals).

For more information on the indications, safety, and use of antivirals in special populations, refer to the product monographs available on Health Canada's Drug Product Database.

Drug Product Database online query

In addition to antivirals, some cases may require respiratory support.

Presently, there is insufficient evidence to suggest added benefit from adjunctive therapies in patients with avian influenza A(H5N1), such as corticosteroids, macrolide antibiotics, and passive immune therapy.

Prevention

Reducing risk of animal-to-human transmission

People who have close contact with poultry, livestock, wild birds, wildlife or other animals that are suspected or confirmed to be infected with avian influenza A(H5N1) should take additional precautions to prevent infection during handling of animals or when working in heavily contaminated environments.

Vaccines against avian influenza may be available for people at highest risk of exposure as another layer of protection, in addition to other preventive measures.

Influenza vaccines statements: National Advisory Committee on Immunization (NACI)

To limit potential risks of transmission through foodborne exposure, safe food handling practices should be followed. At-risk food products should be thoroughly cooked, and all milk and milk products should be pasteurized.

Safe cooking temperatures

Highly pathogenic avian influenza and food safety

It is important for people who hunt and eat wild birds and other wild animals or gather wild eggs to take precautions to help reduce any risk.

Learn more:

Reducing risk of human-to-human transmission

Avian influenza transmission from human to human is extremely rare and has not been sustained, although it is possible. Measures should be taken to reduce the potential spread.

Learn more:

Infection prevention and control of transmission within healthcare settings

For recommendations on additional precautions to prevent transmission when providing patient care, consult the following document:

Notice: Interim recommendations for infection prevention and control of avian influenza in healthcare settings

Recommendations should be read in conjunction with relevant provincial, territorial, and local legislation, regulations, and policies.

For information on biosafety procedures to mitigate the risk associated with handling materials that may contain avian influenza A(H5N1), consult the following document:

Biosafety advisory: Avian influenza A(H5N1)

Learn more:

Vaccines

Avian influenza A(H5N1) clade 2.3.4.4b viruses are circulating in birds and mammals in North America and have caused rare human infections. Health Canada has authorized and purchased a human vaccine against avian influenza (HVAI), Arepanrix™ H5N1 (A/American wigeon clade 2.3.4.4b). HVAI can support a proactive public health response and strengthen Canada's preparedness by complementing other efforts to prevent or reduce the impact of avian influenza A(H5N1).

Arepanrix™ H5N1 (A/American wigeon clade 2.3.4.4b) is:

Provinces and territories have been allocated a limited supply of this vaccine that they may use to respond to avian influenza A(H5N1) in their jurisdiction. NACI advises that the objective of using HVAI in a non-pandemic setting is to prevent human infection with avian influenza A(H5N1) viruses. Preventing transmission from animals to humans could help prevent severe disease in humans and limit opportunities for viral adaptations that could facilitate human-to-human transmission.

Based on this objective, NACI has outlined factors for provinces and territories to consider, including the human and animal epidemiology of avian influenza A(H5N1) when deciding whether and when to start offering HVAI to key populations. Key populations have been identified based on their known or potential risk of exposure to sources of avian influenza A(H5N1). These populations include:

NACI reiterates its recommendation that all individuals 6 months of age and older receive an authorized, age-appropriate seasonal influenza vaccine. This includes people whose occupational or recreational activities increase their risk of exposure to avian influenza A(H5N1) viruses. Although seasonal influenza vaccines do not protect against avian influenza A(H5N1) viruses, they may mitigate the severity of seasonal influenza and reduce the risk of co-infection with seasonal and avian influenza strains.

Learn more:

Public health management

Clinician discretion, epidemiologic context, and local feasibility should be taken into account in discussion with local, provincial and territorial public health authorities when deciding on actions for public health management.

Public health authorities can initiate an investigation and, informed by the initial findings, implement appropriate public health measures to protect human health.

Clinical management of a person who has had exposure to avian influenza A(H5N1)

For a person without any signs and symptoms, health providers should:

For a person with signs and symptoms, health providers should also:

Learn more:

Reporting and surveillance

Provincial and territorial public health authorities are:

Emerging Respiratory Pathogens and Severe Acute Respiratory Infection Case Report Form

For detailed background and recommendations on enhanced severe acute respiratory illness surveillance in hospitals, please consult your local, provincial or territorial health authorities.

PHAC reports any cases of human influenza A of avian origin that are notified globally and within Canada each month.

Human Emerging Respiratory Pathogens Bulletin

The National Microbiology Laboratory reports confirmed positive samples to meet obligations as a national influenza centre and Canada's obligations under the 2005 International Health Regulations.

Canada uses a One Health approach to track avian influenza activity in Canada and around the world.

One Health Approach to Risk Assessment: Executive summary

Canada continually monitors:

Learn more:

Related links

Public Health Agency of Canada

Association of Medical Microbiology and Infectious Disease Canada

U. S. Centers for Disease Control and Prevention

World Health Organization

Page details

Date modified: