Avian influenza A(H5N1): For health professionals
Current situation
Federal, provincial and territorial authorities are currently responding to a widespread outbreak of A(H5N1) across Canada. We're monitoring detections in humans and animals globally, including recent detections associated with dairy cattle in the U.S. The risk of avian influenza infection to people in Canada remains low. Learn more:
On this page
- Key information
- Agent of disease
- Transmission
- Clinical manifestations
- Diagnosis
- Treatment
- Prevention
- Public health management
- Case identification and reporting
- Surveillance
Key information
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, Central and South America, sub-Antarctic regions and Antarctica. Government authorities in Canada are currently responding to the outbreak of influenza A(H5N1) in farmed birds and wildlife across Canada.
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.
Human cases of influenza A(H5N1) have primarily occurred due to zoonotic transmission through direct contact with infected birds (dead or alive) or contaminated environments. 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 (SARI) to facilitate the diagnosis of severe respiratory infection caused by pathogens with epidemic potential.
Antivirals used to treat influenza can be effective in reducing morbidity and mortality, especially if administered early in the course of illness. Prophylactic use of influenza-specific antivirals (pre and post exposure) may prevent illness. Seasonal influenza vaccines do not offer protection against influenza A(H5N1).
Human infections of 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 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 (SARI) 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.
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 A, influenza B, influenza C, and influenza D. 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). To date, 16 HA and 9 NA influenza A subtypes have been detected in wild birds and poultry.
Avian influenza A(H5N1) is classified as highly pathogenic avian influenza (HPAI), based on the severity of illness caused in birds.
Transmission
There are different ways that avian influenza A(H5N1) can be transmitted to humans.
According to the source of infection, transmission can be divided into 4 categories.
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 various sources including: secretions (mucus, saliva), blood and feces as infected animals (virus is shed in secretions and feces).
Transmission can occur during:
- close contact with infected domestic or wild animals
- exposure to highly contaminated environments such as animal farms or live animal markets
- exposure to higher risk environments such as backyard or small flocks
Human infection has been reported after de-feathering of influenza A(H5N1) infected dead swans, and it has been determined that the influenza A(H5N1) virus can survive in feathers for several weeks in moderate temperatures, and over 5 months in cooler temperatures.
Avian influenza A(H5N1) is not well adapted to mammals; however, there have been increasing reports of instances where non-human mammal-to-mammal transmission may have occurred. While rare, transmission from an infected mammal to a human is thought to be possible; however, evidence is currently limited.
Mutations found within some of the Eurasian/North American reassortant influenza A(H5N1) strains circulating in North American birds and mammals in 2022 to 2024 have been shown to enhance polymerase activity and replication in mammalian cells, help evade the immune response, and increase virulence in mice experimentally. As well, recent preliminary findings from pathogenicity and transmissibility studies indicate that the reassortant influenza A(H5N1) strains cause more severe illness in ferrets, increasing concerns about the potential for transmission to humans.
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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 fully cooked poultry, beef, game meat, organs or eggs can transmit the influenza A(H5N1) virus to humans. All evidence to date indicates that thorough cooking will kill the virus. Safe food handling and preparation and good hand hygiene are always important. Pasteurized milk and pasteurized milk products remain safe to consume.
Traditional foods such as wild geese and ducks and harvested wild bird eggs are important sources of food for many Canadians. Although the risk of being infected with avian influenza A(H5N1) from wild birds, wild animals and wild bird eggs is low, hunters and people who handle, prepare and cook wild birds, wild animals and wild bird eggs may be at a higher risk.
Based on the limited research and information available, we do not know at this time if influenza A(H5N1) viruses can readily be transmitted through consumption of raw or undercooked animal products. There have been anecdotal reports of human cases of avian influenza A(H5N1) possibly associated with exposure to raw or undercooked contaminated poultry products, such as raw duck organs and blood. However, to date, there have been no confirmed cases of human infection with A(H5N1) virus acquired through the consumption of food.
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Environmental exposure
The majority of 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 and poultry farms.
Theoretically, humans could get infected with 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 influenza A(H5N1) studies.
Human to human
Evidence of limited human-to-human transmission of influenza A(H5N1) (via close physical contact, for example within a household) has been suggested in previous outbreaks. To date, sustained human-to-human transmission of avian influenza A(H5N1) has never been observed globally.
Clinical manifestations
Avian influenza A(H5N1) in humans mainly affects the respiratory tract. However, it can manifest with gastrointestinal or central nervous system symptoms (e.g., encephalopathy). Clinical illness is seen predominantly in children and young adults.
Most human cases have reported a history of exposure to dead or ill poultry, and the incubation period after exposure is usually 1 to 5 days and up to 9 days.
The clinical manifestations of avian influenza A(H5N1) may include:
- cough
- fever
- shortness of breath
- diarrhea (in severe cases)
- headache
- myalgia
- sore throat
- rhinorrhea
- mucosal bleeding
- fatigue
- jaundice
- conjunctivitis
Imaging studies may show:
- bilateral pulmonary infiltrates
- segmental or lobular consolidation
Based on available human case data to date, the case fatality rate of avian influenza A(H5N1) is approximately 52%. However, this may be an overestimate given that mild infections can go undetected and under-reported. 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 influenza A(H5N1), depending upon region and employment activities.
Respiratory failure is the most common cause of death. Other complications may include:
- multiorgan failure
- pulmonary hemorrhage
- pneumothorax
- pancytopenia
Diagnosis
Clinicians and front line laboratory personnel should consult their local public health unit and the Protocol for Microbiological Investigations of Severe Acute Respiratory Infections (SARI) for guidance on appropriate testing, recommended procedures, and prioritization for influenza A(H5N1) investigations if significant exposure history has been established.
Specimen collection types to be considered include: nasopharyngeal swab, throat swab, sputum, bronchoalveolar lavage, and endotracheal secretions.
- While nasopharyngeal swabs are the primary specimen type for seasonal influenza viruses, based on experiences with the pandemic H1N1 and avian influenza infections, multiple specimen types should be collected in cases of severe respiratory infection with a negative nasopharyngeal swab
Influenza A and B RT-PCR with subtyping (H5) should be the primary method for detection of avian influenza A(H5N1). Any positive samples must be shared with the National Microbiology Laboratory (NML) for confirmatory testing and analysis to fulfill NML's obligations as a National Influenza Centre and Canada's obligations under the International Health Regulations and other agreements.
Rapid Influenza Diagnostic Tests should not be used to rule out influenza A infection. In addition to suboptimal sensitivity of these tests, the ability to detect novel influenza viruses, such as avian influenza viruses, is unknown.
Mishandled specimens from patients under investigation for influenza A(H5N1) are a serious risk to all including health professionals collecting samples and laboratory personnel. For more information on preventative measures before taking and accepting samples, refer to the section on infection prevention and control within a healthcare setting.
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 illness onset. Treatment can be initiated while awaiting confirmatory test results and should not be delayed.
There are several antiviral options for the treatment of influenza A(H5N1):
- Neuraminidase inhibitors (oseltamivir, zanamivir, and peramivir)
- Amantadine
- Baloxavir
Individual characteristics and case presentation should be considered when selecting the appropriate antiviral agent. Oseltamivir, zanamivir, and amantadine are available for use in Canada. Baloxavir and intravenous peramivir may be requested through the Special Access Program and approved on a case-by-case basis.
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 to 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).
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.
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) (i.e., corticosteroids, macrolide antibiotics, and passive immune therapy).
Prevention
Reducing risk of exposure
To limit any potential foodborne risks:
- all poultry, beef and other meat, organs and eggs should be thoroughly cooked to kill potential viruses, parasites and bacteria
- all milk and milk products should be pasteurized before consumption
- safe food handling practices should be followed, such as handwashing and keeping raw meat, organs and eggs separate from other food products to avoid cross contamination
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.
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 handing of animals or when working in heavily contaminated environments.
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Vaccines
There is no avian influenza vaccine available in Canada for public use.
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Infection prevention and control of transmission within healthcare settings
Refer to PHAC's Routine Practices and Additional Precautions for Preventing the Transmission of Infection in Healthcare Settings for recommendations on routine practices to prevent transmission when providing patient care. Recommendations in this guideline should be read in conjunction with relevant provincial, territorial, and local legislation, regulations, and policies.
Information on biosafety procedures to mitigate the risk associated with handling materials that may contain avian influenza A(H5N1) can be found in the Biosafety advisory: Avian influenza A(H5N1).
Public health management
Upon notification of an avian influenza A(H5N1) outbreak with potential human health implications, it is recommended that public health authorities initiate an investigation and, informed by the initial findings from the epidemiologic assessment of the outbreak, implement appropriate public health measures to protect human health.
For management of people who have been exposed to infected animals (wild or domestic) or their environment:
- provide advice on self-monitoring for symptoms for 10 days after last exposure to infected animals or contaminated environment
- evaluate for antiviral prophylaxis
- if symptoms develop:
- obtain diagnostic specimens
- exposed individuals should isolate away from others and use personal protective measures to prevent further spread
For management of human cases in the community:
- complete a case report form, as required
- facilitate collection of appropriate diagnostic specimens
- provide information to the case about their illness and how to access medical care if their illness becomes more severe
- instruct the case to isolate away from others
- ensure no direct contact with animals, including livestock and/or companion animals
- provide information on preventing infection spread to other household contacts
- facilitate access to supportive care and early antiviral treatment, as applicable
- conduct active surveillance and document course of illness as required
- identify and monitor any close contacts
- close contacts are individuals who have been in close proximity of a confirmed or probable case of influenza A(H5N1). They could have also occupied the same area for a prolonged duration of time, or have had direct contact with infectious secretions of a confirmed or probable case of influenza A(H5N1)
The following resource provides additional information on human case and contact management of suspected human infections associated with an animal influenza A(H5N1) outbreak:
- Public health management of human cases of avian influenza and associated human contacts
- Human health issues related to avian influenza in Canada
- Public health measures: Canadian pandemic influenza preparedness: Planning guidance for the health sector
Case identification and reporting
Clinicians and front-line laboratory personnel should follow the Protocol for Microbiological Investigations of Severe Acute Respiratory Infections (SARI). Influenza positive specimens outside the influenza season or obtained from patients with a history of exposure to a potential animal source of influenza should be routinely submitted to the National Microbiology Laboratory (NML) for characterization.
Technical information on avian influenza A(H5N1) and laboratory safety can be found in the Pathogen safety data sheets: Infectious substances – Influenza A virus subtypes H5, H7 and H9.
Provincial/territorial public health authorities are:
- advised to continue vigilance for the recognition, reporting and prompt investigation of patients with Severe Acute Respiratory Illness (SARI)
- required to report confirmed and probable human cases of avian influenza A(H5N1), irrespective of illness symptoms or severity, to PHAC within 24 hours of their own notification as per the Emerging Respiratory Pathogens and Severe Acute Respiratory Infection (SARI) case report form
Surveillance
For detailed background and recommendations on enhanced SARI 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 in the Human Emerging Respiratory Pathogens Bulletin.
Canada uses a One Health approach to track avian influenza activity in Canada and around the world.
Canada continually monitors:
- outbreaks of avian influenza in animals
- human cases of avian influenza
Related links
- Public Health Agency of Canada:
- Notice: Interim recommendations for infection prevention and control of avian influenza in healthcare settings
- Avian influenza A(H5Nx): Public health knowledge gaps and research needs
- Public Health Agency of Canada Expert Panel on Avian Influenza A(H5Nx) in Canada
- Emerging respiratory pathogens
- Human health issues related to avian influenza in Canada
- National case definitions: Human infections with avian influenza A(H5N1) virus
- Association of Medical Microbiology and Infectious Disease Canada:
- U. S. Centers for Disease Control and Prevention:
- Interim guidance on testing and specimen collection for patients with suspected infection with novel influenza A viruses with the potential to cause severe disease in humans
- Influenza antiviral medications: Summary for clinicians
- Interim guidance on the use of antiviral dedications for treatment of human infections with novel influenza A viruses associated with severe human disease
- World Health Organization:
- Influenza H5N1
- World Health Organization fact sheets: Influenza (Avian and other zoonotic)
- WHO guidance on public health measures in countries experiencing their first outbreaks of H5N1 avian influenza
- Protocol to investigate non-seasonal influenza and other emerging acute respiratory diseases
- Summary of key information practical to countries experiencing outbreaks of A(H5N1) and other subtypes of avian influenza
- Guidelines for the clinical management of severe illness from influenza virus infections
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