Avian influenza

Avian influenza, sometimes referred to as “bird flu”, refers to zoonotic type A influenza viruses that typically infect wild waterfowl (e.g., ducks, geese, and swans) and shore birds. These viruses have circulated for over a century, and have caused outbreaks and global pandemics in the past. Infected wild birds can transmit viruses locally to wild or domestic birds and mammals or facilitate the movement of the virus over large migratory ranges.

Avian influenza A viruses are categorized based on their pathogenicity to birds — either low pathogenicity avian influenza (LPAI) or high pathogenicity avian influenza (HPAI). It is important to note that these designations do not equate to pathogenicity, or severity of illness, in humans. One HPAI virus circulating globally is A(H5N1), which can easily transmit between different bird species with a very high mortality rate. The A(H5N1) outbreak affecting North America since 2021 has been driven by clade 2.3.4.4b, which has evolved to infect a wider range of bird species and mammals than has ever been seen before, including dairy cattle and pigs in the US for the first time in 2024.

The first reported human infection with A(H5N1) occurred in Hong Kong in 1997. Between 2003-2024, there have been over 930 human infections with A(H5N1) reported to the World Health Organization (WHO). Of these, 464 people have died, most prior to 2020. There may have been underreporting of mild or asymptomatic cases in previous outbreaks. In the current outbreak, there have been over 55 human infections reported in the United States (US), most of which have been mild and were associated with exposure to either infected cattle or poultry. Some infections have likely gone undetected, as indicated by serologic test results of some US dairy farm workers exposed to infected cows. The first ever case of domestically acquired A(H5N1) infection in Canada occurred in 2024 and resulted in critical illness and hospitalization of the individual. This Canadian case and two cases in the US have no confirmed exposure source.

While avian biosecurity measures to protect poultry from HPAI are well established, the persistence of the A(H5N1) outbreak in North America and the increased spread to mammals, including humans, underscores the need for continued vigilance to prevent spread and opportunities for viral evolution and reassortment with other influenza viruses. The resources listed here are intended to assist environmental public health practitioners to identify where the virus is being detected, how the virus is transmitted, and the public health measures that can help reduce transmission.

For reporting of sick or dead wildlife in Canada, find Provincial and Territorial contacts, advice, and an online reporting tool on the Canadian Wildlife Health Cooperative website.

Surveillance and dashboards

These dashboards and websites report on the current situation related to infections in poultry, wild animals, and humans in Canada, the US and globally.

Canada

• Status of ongoing avian influenza response by province (CFIA, 2024)
  This website lists the number of Canadian premises with infected domestic flocks by province and links to additional information on investigations and control orders. Also see: Map: Highly pathogenic avian influenza zones

• High pathogenicity avian influenza in wildlife (ECCC/CWHC/CFIA, 2024)
  This Canadian dashboard reports suspected and confirmed cases of HPAI in wild birds and mammals detected across Canada since 2021. Data can be filtered by date, province, and species.

• HPAI detections in BC: Wildlife and environmental surveillance (BCCDC, 2024)
  This BC dashboard provides a weekly intelligence update and reports on HPAI detections in wild animals and sediments collected across BC.

• Rapid risk assessment update: Avian influenza A(H5N1) clade 2.3.4.4b, public health implications for Canada
  This risk assessment summarizes the likelihood of infection with influenza A(H5N1) from exposure to birds and mammals, including livestock, for the Canadian public and for people with higher levels of exposure, and the likelihood and impact of human infection following exposure. 

US/Global

• Detections of highly pathogenic avian influenza (US Dept of Agriculture, 2024)
  This website provides links to additional information and dashboards reporting on US detections of HPAI viruses in commercial and backyard flocks, wild birds, mammals, and livestock.

• H5 bird flu: Current situation (US CDC, 2024)
  This website provides an overview of the current avian influenza situation in the US, including reported human cases, national flu surveillance, and targeted H5 surveillance activities.

• Highly pathogenic avian influenza virus detection in Europe (European Food Safety Authority, 2024)
  This interactive map provides an overview of detections of avian influenza (H5 and H7 subtypes) in poultry and wild birds in continental Europe.

• Avian influenza: Global situation (World Organization for Animal Health, WOAH, 2024)
  This website provides information on HPAI activity at the regional and global level using information submitted to the World Animal Health Information System (WAHIS). The global situation reports are updated every 3-6 weeks, with a summary and contextual information of HPAI activity.

• Avian influenza A(H5N1) virus. Risk assessment and management (WHO, 2024)
  This website provides the most recent FAO/WHO/WOAH assessment of risk, technical guidance, and the reporting on cumulative confirmed human cases reported to the WHO since 2003.

Transmission of HPAI to birds and mammals

The A(H5N1) clade 2.3.4.4b currently circulating in North America is better adapted to infect a wider range of bird species and mammals than in previous A(H5N1) outbreaks. The following resources provide information on understanding transmission and evolution of the virus.

• Animals susceptible to H5N1 highly pathogenic avian influenza (HPAI) (CFIA, 2024)
  This website provides information on the signs and symptoms of H5N1 HPAI in animals including birds, dairy cows, farmed mink, and pet cats and dogs. (Further information on preventing and detecting disease in small flocks and pet birds can be found here)

• The global H5N1 influenza panzootic in mammals (Peacock et al., 2024)
  This review article provides further information on evolution and pandemic potential of A(H5N1) based on three case study of A(H5N1) outbreaks where mammal-to-mammal transmission may have occurred – European fur farms, South American marine mammals, and US dairy cattle.

• Avian influenza A(H5N1) virus in dairy cattle: origin, evolution, and cross-species transmission (Mostafa et al., 2024)
  This review article discusses the epidemiology, pathogenesis, and impact of the HPAI outbreak in dairy cattle in the US, with consideration of the public health implications and control measures.

• CAHSS dairy network (Canadian Animal Health Surveillance System, 2024)
  This website provides an information portal for the dairy industry and others to follow the A(H5N1) outbreak in US cattle. More on CAHSS’s activities related to HPAI outbreak preparation and response can be found in the Oct 2024 NCCEH webinar recording.

• Avian influenza A(H5N1) and the continuing outbreak (O’Keeffe, 2023)
  This NCCEH evidence brief provides an overview of the literature on transmission of A(H5N1) between birds and to other animals and humans. Considerations for managing the environmental, animal, and human drivers of transmission using a One Health perspective are presented.

HPAI in food sources

With HPAI being detected in US dairy cattle in 2024, there is renewed interest in the occurrence of HPAI in food sources. This section provides information on what is known about HPAI in food, including meat, milk, and eggs, and the effectiveness of thermal treatment (cooking and pasteurization) for inactivating the virus.

• Highly pathogenic avian influenza (HPAI) and food safety (Government of Canada, 2024)
  This website addresses whether HPAI is a food safety concern in Canada and provides general advice on safe food practices, safe cooking temperatures, pasteurization, and related information.

• Avian influenza A(H5N1) in dairy farms: An update on public health and food safety concerns (O’Keeffe and Goulding 2024)
  This NCCEH blog provides background information on transmission pathways for avian influenza A(H5N1), the emergence of infections in US dairy cattle, and implications for food safety.

• Highly pathogenic avian influenza (HPAI) in livestock (CFIA, 2024)
  This website provides information on HPAI for livestock producers, consumers, veterinarians, and the status of commercial milk testing in Canada. 

• Survivability of influenza A(H5N1) in milk (Public Health Ontario, 2024)
  This rapid review summarizes a scan of available information and guidance from Canada, the US, and the UK on the survivability of influenza A (H5N1) virus in milk sourced from infected livestock.

• Persistence of influenza H5N1 and H1N1 viruses in unpasteurized milk on milking unit surfaces (Le Sage et al., 2024)
  This research article provides information on the levels of infectious virus detected in the raw milk of infected dairy cows and discusses the potential pathways for dairy workers interacting with cows and milking equipment to become exposed to the virus.

• Investigation of avian influenza A (H5N1) virus in dairy cattle (US FDA, 2024)
  This website provides information on the status of the milk supply in the US, communications to dairy processors and retailers, and results of bulk milk silo studies and retail sample surveys.

• Influenza A in U.S. dairy cattle 2024 (Western Canadian Animal Health Network, 2024)
  This website provides an overview of the current situation including HPAI in US dairy workers, US dairy cattle, detections in commercial and raw milk, regulatory responses, and biosecurity resources.

• Thermal inactivation of influenza A(H5N1) in meat (Public Health Ontario, 2024)
  This rapid review summarizes what is known about the time and temperature for inactivation of A(H5N1) virus in meat, including poultry and beef.

• Questions and answers regarding the safety of eggs during highly pathogenic avian influenza outbreaks (US FDA, 2024)
  This guidance document provides information on the safety of retail eggs in the US. The risk of HPAI infection through consumption of contaminated eggs is characterized as low.

Public health measures for preventing spread

The resources below aim to improve understanding of HPAI transmission pathways between animals and from animals to humans, alongside measures for preventing exposures and infection.

• Avian influenza A(H5N1): Prevention and risks (PHAC, 2024)
  This website provides information on occurrence and spread of avian influenza, understanding risks, recommendations for travellers and advice for those who work with animals. Minimizing contact with secretions (mucus, saliva), blood, or feces from infected animals is key to preventing infections.

• Wildlife and avian influenza – handling guidelines to protect your health (PHAC, 2024)
  This website provides recommendations for the public, hunters, and people who work with wildlife to prevent exposure to HPAI when handing sick, injured, or dead animals and when preparing game meat, organs, or harvested eggs.

• Avian influenza (BC Centre for Disease Control, 2024)
  This website provides an overview on the current avian influenza situation and information and resources on HPAI in wild birds, wild animals, poultry, livestock, people, pets, and food safety. Also see the helpful factsheet: Avian Influenza (bird flu) in B.C. How can I protect myself?

• Avian influenza (Canadian Centre for Occupational Health and Safety, 2024)
  This website provides answers to FAQs and resources for workers who may be exposed to HPAI at work, including an infographic on How to protect yourself from avian influenza at work.

• Avian influenza (bird flu) resources (US CDC, 2024)
  This resource collection provides factsheets, infographics, and other tools in multiple languages for farm workers, farm owners, and others who work with poultry or cows to increase awareness of HPAI transmission and understanding of prevention and protection measures.

• Personal protective equipment use by dairy farmworkers exposed to cows infected with highly pathogenic avian influenza A(H5N1) viruses — Colorado, 2024 (Marshall et al., 2024)
  This research article provides information on the effectiveness of public health interventions to increase the use of personal protective equipment on dairy farms with A(H5N1) virus-infected cows.

• Practical guide for authorized field responders to HPAI outbreaks in marine mammals (WOAH, 2024)
  This guidance document provides information on dealing with a mass outbreak of A(H5N1) in marine mammals with a focus on biosecurity, sample collection, and safe carcass disposal. 

• Reducing health risks associated with backyard chickens 2^nd Edition (PHO, 2023)
  This evidence brief summarizes literature on the awareness of backyard chicken owners on infectious disease risks from backyard flocks, and risk reducing measures for zoonotic infections.

• Highly pathogenic avian influenza: Infection prevention and control guidance for veterinary clinics (PHO, 2023)
  This guidance document provides information on recognizing the clinical signs of HPAI in animals, IPAC recommendations, reporting and disease prevention.