Avian influenza, or "bird flu," has periodically surfaced as a pressing concern for poultry industries and public health worldwide.
Highly Pathogenic Avian Influenza (HPAI) strains, such as H5N1, are responsible for significant bird and animal outbreaks and have shown the potential to affect humans in rare cases.
With an understanding of HPAI’s history, how it spreads and the importance of biosecurity measures, we can better prepare for and mitigate the risks associated with this virus.
History of HPAI: From Past Outbreaks to Present Challenges
The story of avian influenza isn’t new. While outbreaks were documented in the 20th century, it was the 1997 H5N1 outbreak in Hong Kong that brought HPAI into the global spotlight. Since then, multiple strains of avian influenza have evolved, including H7N9, H5N6 and the infamous H5N1, which have impacted both poultry and humans.
In recent years, HPAI has resurfaced with a vengeance, fueled by migratory patterns of wild birds that spread the virus across borders. The current strains circulating among birds and mammals present new challenges and underline the importance of continued vigilance.
Quick Overview: What is Avian Influenza?
Avian influenza is a highly contagious respiratory virus that primarily targets birds, often causing severe illness and even death, especially in domestic flocks like chickens and turkeys.
Among the different strains, H5N1 is particularly concerning due to its ability to spread quickly and cause devastating effects in both poultry and wild bird populations. More than 100 wild bird species can carry avian influenza, though domestic birds like chickens and turkeys are especially vulnerable, often experiencing higher illness and death rates.
In 2024, H5N1 made headlines with major outbreaks, totaling 45 commercial poultry flocks and 30 backyard flocks affecting over 22 million birds. However, this outbreak hasn’t been limited to just birds—recent cases have shown that H5N1 has spread to cattle, impacting nearly 500 herds across 15 states, and there have even been isolated incidences in humans.
The Rise of HPAI in the 2020-2024 Outbreak
The recent increase in HPAI cases can be traced back to 2020, when viruses in poultry and wild birds reassorted (two viruses that infect the same cell have swapped gene segments causing the virus to evolve and adapt to new species) and the HPAI H5N1 virus emerged in Europe.
The wild bird-adapted H5N1 virus spread throughout Europe, Africa, Asia and the Middle East, but it was not until January of 2022 that the H5N1 virus was detected in the United States in wild birds. Within approximately a month of this wild bird detection, the H5N1 virus had spread to a commercial turkey flock, the first HPAI detection in a U.S. commercial poultry operation since an outbreak of H7N3 in 2020.
Since February 8th, 2022, over 115 million commercial and backyard birds have been affected by HPAI in the U.S., largely affected by wild bird migration patterns, which help spread the virus across regions.
In March of 2024, after Texas dairy cows had shown signs of an unknown illness, it was discovered that the culprit was H5N1. This detection in dairy cows was the first of its kind during the current outbreak and has since spread across 15 states with a total of 720 confirmed H5N1 cases in dairy cows.
One week after the first confirmed case of H5N1 in a dairy cow, the first human case of the virus since a poultry farm worker tested positive in 2022 was confirmed, presumably because of the patient’s exposure to a dairy cow infected with the virus. Since this case in April of 2024 there have been a total of 58 confirmed human cases of H5N1, most of which are assumed to be a result of exposure to infected dairy cows, but exposure to infected poultry species has also been linked to human cases.
There is currently no evidence showing human-to-human spread of the H5N1 virus, but health organizations like the Center for Disease Control (CDC), United States Department of Agriculture (USDA) and World Health Organization (WHO) are keeping a close eye on the current situation. These organizations are constantly looking for trends and monitoring outbreaks for any changes in the virus that could increase the risk to human health.
How Do Humans Get Avian Influenza?
Human infection typically happens when avian influenza virus particles enter the body through the eyes, nose or mouth, often through inhaling droplets or aerosols (small particles in the air) from infected birds or by touching contaminated surfaces and then touching the face. Human-to-human transmission remains exceptionally rare, but symptoms for those infected can include flu-like symptoms, conjunctivitis (eye infections) and even pneumonia.
Can Avian Influenza Kill Humans? What Happens if a Human Contracts it?
While avian influenza rarely infects humans, certain strains can cause severe illness or death. Strains like H5N1 and H7N9 have been historically associated with high fatality rates in Asia, primarily due to respiratory complications, but there have been no human deaths and little severe illness due to H5N1 in the U.S. during the current outbreak. While human-to-human spread remains rare, health officials are emphasizing the importance of vigilance in monitoring potential disease symptoms for those who are in contact with livestock and poultry species.
The Key Avian Influenza Strains Impacting Birds and Humans
The CDC identifies three strains of avian influenza—H5N1, H5N6 and H7N9—as particularly concerning due to their severe effects on birds and their potential to occasionally infect humans. These strains are highly aggressive in birds, often causing high mortality rates in poultry and spreading rapidly within and between flocks.
Here’s a quick breakdown:
H5N1: The H5N1 avian influenza strain was first identified in domestic geese in China in 1996, although low-pathogenic variants were documented as early as 1959 in Scotland. For birds, H5N1 is especially devastating, with outbreaks causing extremely high mortality rates in both commercial and backyard poultry flocks, often requiring drastic measures like culling to control its spread. While H5N1 can infect humans, resulting in severe respiratory illness and a high fatality rate in past cases, it remains primarily a threat to bird populations with today’s strains.
H5N6: Emerging in Asia, particularly in China, H5N6 has led to outbreaks in poultry and sporadic human infections since 2014. While human cases are rare, H5N6 hits birds hard, especially in high-density poultry settings. Outbreaks in poultry flocks result in high death rates and spread quickly through both commercial and backyard environments.
H7N9: First detected in China in 2013, H7N9 is a bit of a sneaky strain. It circulates among poultry without causing visible illness, so infected birds often look perfectly healthy. This “silent” spread means the virus can move through flocks and even live poultry markets without being noticed, making it difficult to control. Although H7N9 has led to severe cases in humans, it’s primarily a risk to birds.
The Role of Vaccines in Combatting Avian Influenza
During this outbreak, there has been an increasing focus on avian influenza vaccine development. Researchers have been making headway on an H5N1 vaccine for birds, livestock and humans, with some exciting work being done on mRNA vaccines by the University of Pennsylvania.
Several countries such as France, China and Mexico currently have protocols and approved vaccines for their flocks to fight avian influenza. In the U.S., the USDA has started vaccine trials for birds, aiming to manage the spread among domestic flocks. However, it is unclear whether these vaccines will be approved for use in commercial U.S. poultry because of trade restriction challenges.
On the flip side, the USDA has two avian influenza vaccines for use in dairy cows in the field trial stage. It is likely we will see an avian influenza vaccine for dairy cattle approved for use in the U.S. before a similar poultry vaccine. But before these can roll out on a large scale, challenges like trade restrictions with other countries need to be worked out.
For humans, vaccines are also in the works. In the United States, the CDC and WHO are developing an mRNA vaccine for H5N1 to help protect people in high-risk situations. And in other countries, progress is being made with avian flu vaccines, which could be key in stopping global outbreaks.
Vaccine Development at University of Pennsylvania
Researchers at the University of Pennsylvania, led by Dr. Scott Hensley and Dr. Drew Weissman at Penn Medicine, are making significant progress in developing an mRNA vaccine to combat the H5N1 bird flu virus.
Dr. Hensley, an expert in viral immunology, and Dr. Weissman, a pioneer in mRNA vaccine technology, bring substantial expertise to this research effort. Dr. Weissman’s previous work contributed to the rapid development of COVID-19 mRNA vaccines, marking him as a leader in the field.
The preclinical trials of the Penn H5N1 mRNA vaccine has shown promising effectiveness in preventing severe illness and death in test models. This suggests that the vaccine could significantly reduce mortality and illness in those infected by H5N1, including at-risk animal populations like birds and cattle.
How Avian Influenza Spreads in Birds
Avian influenza spreads fast among birds, mainly through contact with saliva, nasal secretions or droppings from infected birds. Birds can pick up the virus through inhalation of particles or dust carrying the virus, directly from each other or by touching contaminated surfaces.
Outbreaks can also spread through contaminated equipment, feed and water sources, and even through people, vehicles or supplies moving between farms. This is why following biosecurity measures closely is so important to prevent the virus from spreading.
Biosecurity: Our Best Defense Against Avian Influenza
In the absence of a widespread vaccine, biosecurity measures are our frontline defense against HPAI. Biosecurity encompasses all practices that limit the introduction and spread of pathogens within poultry operations. Effective biosecurity can be the difference between containment and an outbreak.
Key Biosecurity Practices Include:
Line of Separation: Establishing a “line of separation” is essential in preventing disease from entering bird areas. This invisible line divides clean areas (like where birds are kept) from potential contamination zones. Workers and visitors should change footwear, use disinfectant mats or wear protective clothing before crossing this line to minimize contamination risks. Get a checklist for your line of separation here.
Cleaning and Disinfection Protocols: Effective cleaning and disinfection are crucial in eliminating HPAI viruses from farm facilities. The USDA, Animal and Plant Health Inspection Service (APHIS) recommends using either wet or dry cleaning methods to remove organic matter from equipment and structures before applying disinfectants.
Wet cleaning involves the use of water and detergent to remove organic material, followed by rinsing and applying disinfectants.
Dry cleaning is useful in colder weather or when water access is limited and involves removing organic matter (like dust and debris) without water, making disinfectants more effective afterward.
Heat Treatment: Heat is a proven method for inactivating viruses, including HPAI. APHIS advises using heat treatment in addition to dry cleaning, particularly when the virus is suspected to be on surfaces that can withstand high temperatures. For example, heating poultry houses to a minimum of 120°F for seven days can help destroy lingering pathogens.
All-in, All-out Management: Farms should aim to keep flocks isolated by implementing an “all-in, all-out” approach, which involves removing all birds from an area before introducing a new flock. This breaks potential virus transmission cycles and minimizes cross-contamination between flocks.
Controlled Access: Limiting on-site access to essential personnel and ensuring vehicles and equipment are disinfected thoroughly before entry is essential to biosecurity. Disinfecting vehicle tires, undercarriages and any equipment minimizes the risk of introducing contaminants from outside areas.
Wild Bird Deterrence: Wild birds are common carriers of avian influenza. Physical barriers, such as netting or fencing, can prevent contact between wild birds and domestic poultry. Deterrents like bird lasers can also be effective in discouraging wild birds from roosting or flying over poultry facilities, helping reduce potential exposure. Check out the new Ai powered lasers poultry farms are using to protect their farms.
Rodent Management: Rodents are a biosecurity risk, carrying diseases, contaminating feed and damaging infrastructure. Effective control includes monitoring, removing food and water sources, sealing entry points, setting traps in key areas and keeping areas clean and debris-free to deter rodents and reduce disease transmission.
Clothing and Equipment Sanitation: Providing workers with dedicated, disinfected clothing and footgear is essential to minimize cross-contamination risks. APHIS recommends that employees have access to disinfection facilities, especially before entering and after leaving poultry houses. Additionally, limiting the transfer of equipment between farms helps prevent virus spread.
How to Audit Your Biosecurity Program
Auditing your biosecurity program is key to keeping everything running smoothly and making sure you’re hitting the highest standards for disease prevention.
Here’s a quick guide to help you audit your program:
Review Your Written Plan: Start by going over your written biosecurity plan to confirm it includes all the essentials:
Access control measures.
Detailed cleaning routines.
Pest control strategies.
Do a Facility Walk-Through: Take a walk around the facility and check that:
Fences and barriers are in place to keep wild birds and animals out.
Cleaning routines are on point, with the right methods and disinfectants being used.
Ensure all disinfectants are EPA-approved antimicrobials for avian influenza.
Check Entry and Exit Protocols: Look at how people are moving in and out.
Confirm that only essential personnel enter restricted areas.
Make sure proper disinfection steps are followed each time someone enters or exits.
Focus on Employee Training: Keep your team well-informed.
Ensure everyone understands biosecurity protocols.
Provide regular refresher training so everyone stays sharp on procedures.
Review Record-Keeping: Look at cleaning logs, visitor records and other documentation to get a sense of how consistently biosecurity measures are being followed.
Run Emergency Drills: Occasionally run outbreak response drills so the team knows exactly what to do in case of an emergency.
Following these steps makes it easier to stay on top of biosecurity, keeping your facility safe and compliant.
The Road Ahead
The good news is that HPAI doesn’t spread easily from person to person, making a human pandemic pretty unlikely. Most human cases come from direct contact with infected birds, and reports of the virus spreading between people are extremely rare, which is reassuring as experts continue to monitor it closely.
Looking forward, vaccine development for both birds and humans is progressing, and biosecurity practices are improving. New technology like bird-deterrent lasers and better diagnostic tools are also helping to detect and contain outbreaks faster, giving us more ways to protect both birds and people in the future.
Resources and Tools to Monitor Avian Influenza
The fight against avian influenza is ongoing, but with the right tools and information, we can stay a step ahead! For updates on bird migration patterns and the current state of avian influenza, check out these resources below:
U.S. Bird Migration Map: BirdCast Interactive Map - View real-time migration data, including bird density and travel patterns.
Avian Influenza Impact by Species and Region: CDC’s Situation Summary
For any questions on avian influenza, contact Ralco’s poultry team at 1-800-533-5306 or email us at info@ralcoagriculture.com.
References:
Penn Medicine: World-Changing mRNA Vaccines from Penn Medicine
Penn Medicine: Penn Researchers Develop Experimental mRNA Avian Flu Vaccine
USDA: HPAI Response Cleaning & Disinfection Basics (Virus Elimination)
Indianna State Board of Animal Health: Highly Pathogenic Avian Influenza Information and Biosecurity
Mississippi State Extension: Controlling Rodents on the Poultry Farm