Avian influenza, commonly known as bird flu, is a type of influenza virus that primarily circulates among wild aquatic birds. This virus can cause disease in a wide range of bird species, including domesticated poultry. Its presence is a topic of global health interest because these viruses have the capacity to evolve and potentially infect other animal species, and in rare instances, humans. Understanding avian influenza involves recognizing its different forms and how it moves through populations.
What is Avian Influenza?
Avian influenza is caused by influenza A viruses, distinct from the viruses that typically cause seasonal human flu. These viruses are categorized by two surface proteins: hemagglutinin (H) and neuraminidase (N), leading to various subtypes like H5N1, H7N9, and H9N2. The H5N1 subtype, particularly highly pathogenic avian influenza (HPAI) H5N1, has been a significant concern since its emergence in 1996 due to its severity and widespread impact globally. This strain has led to widespread mortality in wild birds and poultry across Africa, Asia, Europe, and the Americas since 2020.
HPAI viruses cause severe illness and high death rates in infected poultry, leading to widespread outbreaks and significant losses. The virus can also infect mammals, including marine mammals, wild and domestic cats, and recently, dairy cows.
How Avian Flu Spreads
Avian influenza viruses primarily spread among birds through their saliva, mucus, and feces. Wild aquatic birds are natural carriers of these viruses and can spread them through migration, often without showing signs of illness. This widespread presence in wild bird populations can then lead to spillover events into domestic poultry farms, causing outbreaks.
The virus can then transmit to mammals through direct contact with infected animals or environments contaminated with the virus. Human infections, while rare, typically occur through direct, prolonged contact with infected birds or environments contaminated with the virus.
Transmission in Dairy Cattle
Recent instances in dairy cattle have brought new insights into transmission mechanisms. Movement of infected cattle and contaminated equipment were initially considered primary routes, but ongoing outbreaks have prompted investigations into other factors. Research suggests that “milk snatching,” where lactating cows self-nurse or mutually nurse, could facilitate mouth-to-teat transmission, allowing the virus to infect mammary glands. Additionally, calves with the virus in their mouths have been found capable of transmitting it to the mammary glands of cows they nurse. House flies have also been identified as potential mechanical vectors, meaning they can carry the virus on their bodies and spread it between farms, though there is no evidence they transmit it to humans or other animals directly.
Public Health Monitoring and Preparedness
National and international health organizations play a role in monitoring avian flu outbreaks and assessing pandemic risk. The World Health Organization (WHO), the Centers for Disease Control and Prevention (CDC), and the World Organisation for Animal Health (WOAH, formerly OIE) collaborate to track new variants and guide response efforts. Surveillance systems are in place to monitor influenza activity in humans and animals year-round. Every identified human case of novel influenza, which includes infections with non-human influenza A viruses, is investigated and reported to the CDC.
These organizations focus on strengthening early warning systems, ensuring affected countries and international bodies have the necessary data and specimens for accurate risk assessment. Rapid containment operations are intensified to prevent human-to-human transmission or delay international spread. Biosecurity measures at governmental and industry levels, such as those implemented on farms, are also emphasized to reduce the risk of disease transmission. Research into vaccine development for both animals and humans is ongoing, with global procedures in place to quickly update candidate vaccine viruses and produce adapted vaccine components for any influenza virus.
Safeguarding Against Avian Flu
Individuals can take practical steps to reduce their risk of exposure to avian influenza. Handwashing immediately after contact with animals or their environment is a simple yet effective hygiene practice. Avoiding touching eyes, nose, and mouth with unwashed hands is also important.
To safeguard against avian flu, consider these measures:
- Ensure poultry and eggs are cooked to an internal temperature of at least 165 degrees Fahrenheit.
- Avoid consuming raw or unpasteurized milk and raw milk products, as pasteurization effectively kills the virus and other harmful microbes.
- Avoid contact with sick or dead wild birds or mammals without appropriate protective measures like wearing gloves.
- If multiple dead birds are found, local authorities should be informed for proper disposal.
- Follow advisories from local public health authorities for current guidance on specific precautions.