Bird flu – Overview and Background of Avian Influenza – 03/Apr/2024

## The Resurgence of Avian Influenza: Understanding the Global Impact and Risks

Avian influenza, also known as bird flu, is a highly contagious viral disease affecting various bird species. This infection can lead to significant economic losses in the poultry industry and poses risks to human health. With periodic outbreaks making headlines, understanding the nature of the disease, its transmission, and the measures to control it is of global importance.

Overview and Background of Avian Influenza

Avian influenza refers to the disease caused by infection with avian (bird) influenza (flu) Type A viruses. These viruses occur naturally among wild aquatic birds worldwide and can infect domestic poultry and other bird and animal species. Bird flu viruses do not normally infect humans. However, sporadic human infections with bird flu viruses have occurred. The most well-known strain, H5N1, has been of particular concern due to its potential for severe impacts on both birds and humans.

Types and Strains of Bird Flu Viruses

There are various types of avian influenza viruses that are categorized based on their ability to cause disease (pathogenicity) in birds. The two main categories are low pathogenic avian influenza (LPAI) which typically causes few or no signs of disease in birds, and highly pathogenic avian influenza (HPAI), which can lead to high mortality rates among poultry.

Within these categories, viruses are further classified by their surface proteins: hemagglutinin (H) and neuraminidase (N). The H5N1 strain is the most infamous highly pathogenic virus, with widespread outbreaks in domestic poultry and the capacity to cause severe diseases in humans.

Transmission and Spread of Avian Influenza

The primary mode of transmission for avian influenza A viruses between birds is through direct contact with infected individuals or contaminated environments. Wild migratory birds such as ducks, geese, and swans are natural hosts for these viruses but generally do not show symptoms. They can spread the virus long distances along their migration routes.

The spread of bird flu in commercial production systems can occur rapidly due to dense stocking densities, as well as through movements of poultry products, equipment, vehicles, feed, cages or even through clothing and shoes of farm workers.

Impact on Poultry Industries

HPAI can have a devastating impact on the poultry industry due to the high mortality rates in birds and the necessary culling of entire flocks to prevent further spread. Restrictions on trade of birds and related products from infected areas further exacerbate economic losses.

Human Health Risks

Though they do not easily infect humans, HPAI viruses like H5N1 are zoonotic pathogens—they can cross species barriers and infect humans from birds. When such cross-species transmission occurs, the effects can be severe and lead to serious disease or death.

Prevention and Biosecurity Measures

Preventing avian influenza involves following stringent biosecurity measures on poultry farms. This includes isolating poultry from wild birds, using disinfectant foot baths at farm entrances, controlling pests, and ensuring feed and water are not contaminated.

Vaccination may also play an essential role in protecting poultry from AI viruses; however, vaccines need to be closely matched to circulating strains and may only be available for certain subtypes.

Global Surveillance and Reporting

Continuous surveillance capabilities are essential to rapidly detect new cases of avian influenza in both animals and humans. Prompt reporting allows for immediate response actions to contain outbreaks before they have wider spread implications.

Efforts by International Organisations

Organisations like the World Health Organization (WHO), the Food and Agriculture Organization of the United Nations (FAO), and the World Organisation for Animal Health (OIE) work closely together to monitor global trends in avian influenza strains and advises government’s mitigation techniques.


  • The highly pathogenic avian influenza H5N1 virus has caused the deaths of millions of poultry since its large-scale emergence in 1996.
  • Human cases of bird flu infections have resulted in a nearly 60% mortality rate for infected individuals since 2003 according to WHO data.
  • The economic cost of the 2014–2016 HPAI outbreak in the US has been estimated at nearly $3 billion.
  • Updated vaccines must be formulated annually as virus strains mutate over time, complicating prevention efforts.
  • *Image description: A cautious-looking farmer in protective clothing inspecting chickens inside a large commercial poultry house filled with long rows of containment areas for individual chickens. Signs on the walls indicate biosecurity measures are being implemented.*