The Egg-scalating Spread of Avian Influenza Across the United States

Described by the United States Department of Agriculture as the “most expensive animal heath incident recorded in U.S. history”, the 2014-2015 avian influenza outbreak rocked the United States. 

Between December 2014 and June 2015, it was estimated that 50.4 million domestic poultry (i.e., turkeys and egg laying chickens) died across 21 states. This outbreak cost approximately $3.3 billion from egg production loss, restocking, and loss of future production and $850 million dollars in ‘cleanup’ (e.g., depopulation, disposal, and cleaning/disinfection of the premises). After this event, new procedures were put in place by the USDA to mitigate future outbreaks, minimizing the number of birds lost. However, despite these procedures, a new outbreak of the “Bird flu” began in February of 2022, which appears to be on-track to match or surpass the “most expensive animal health incident recorded in U.S. history”.

A sign on the side of a road

Description automatically generated with medium confidence
Avian Influenza Sign  (Image credit: Keith Evans, CC BY-SA 2.0)

Avian influenza (AI) is a viral respiratory disease that affects all avian species. Like human influenza, AI frequently mutates overtime and is classified into either high pathogenicity (HPAI) or low pathogenicity (LPAI) avian influenza. LPAI is commonly found in wild birds and occasionally is introduced into domestic flocks. HPAI is less common than LPAI, in both wild and domestic settings, particularly in countries like the United States with a more developed veterinary infrastructure and advanced animal agricultural industries. Outside of the United States, these variants have been found in 29 European countries and 10 other countries throughout the world. 

HPAI is far more infectious, spreading through a flock rapidly via respiratory secretions and feces. It can also be spread through indirect contact, such as being spread between individuals or flocks from the farmer’s shoes. Symptoms from an infected individuals include, but are not limited to, decreased food and water consumption, decreased egg production, production of soft or deformed eggs, facial/head swelling, loss of coordination, diarrhea, lack of energy, and even sudden death. Mortality ranges between 90-100% and occurs within 48 hours of infection for HPAI (CDC). 

Migratory waterfowl facilitate the spread of AI as they cross paths with other wild birds during their migrations across states, countries, and even continents. These migrating birds will catch the virus from ducks and geese who are hosts of AI (ducks being the central host for HPAI; Badruzzaman et al. 2022). The virus is then transferred to domestic poultry where infected individuals land on fields or wetlands adjacent to poultry farms. In the United States, 9 billion chickens can be traced back to a few breeds, decreasing the genetic diversity of their immune system, allowing AI to spread like wildfire throughout farms as there is little variation amongst individuals to fight off the virus. 

In February 2022, HPAI began making its way across the United States and by April 29, cases were found in 29 states and more than 36 million domestic poultry have died. This equates to a monthly mortality rate 2.25x larger than in 2015. If this rate continues the U.S. could lose upwards of 72 million birds by June 2022. This might mean that the U.S. could lose more than $2 billion dollars from egg production alone. 

A flock is infected, now what?

Depopulate. Depopulation is the act of killing the entire flock as quickly as possible, ideally beginning 24 hours after first infection. The commonly seen methods are the application of carbon dioxide (CO2) and nitrogen infused compressed air foam, CO2 gas, or a ventilation shutdown. The method selected is based on housing and environmental conditions, currently available resources and personnel, and other relevant factors specific to the infected location. Depending on flock size and species present (e.g., only chickens/turkeys or a mix of poultry), depopulation on average, can take 3.5 to 15.4 days from time of initial infection.

Dispose. After a depopulation, the poultry farm may have hundreds of thousands of diseased poultry needing to be disposed of so the facility can begin disinfecting the premises. The most effective and efficient way is through composting, where the farmers place the carcasses in large piles to decompose. One problem with composting thousands of birds is it has led to some upset neighbors as it smells like death”, with the smell emanating up to a mile away and lasting over a month depending on the weather conditions and wind directions. Alternatives to composting include disposing individuals in a landfill, incineration, or burial.  

Disinfect. Lastly, the areas previously inhabited by infected flocks need to be cleaned and sanitized to remove any remnants of the virus before farmers can begin restocking their flocks.

Why should we care?

The U.S. needs to have 325 million commercial laying hens to meet consumption goals (United Egg Producers of America). 

In 2020, American’s consumed around 286 eggs per year which is roughly how many eggs one hen produces annually (USDA Economic Research Service). As of April 2022, 11% of the animals needed to meet this consumption goal have died. These events have led to a 4.5x price increase on a dozen eggs since April 2021 ($0.52 to $2.34; data collected from Urner Barry). During the 2014-2015 outbreak, egg prices reached nearly $2.80 per dozen. If this trend continues until June, we can expect to see egg prices continue to rise.

Although this is impacting the U.S. economy, this is not just a problem for domestic birds, egg production, and the egg-loving human’s wallet. This is a problem that can have great ecological and cultural ramifications around the world. We’ve recently seen the death of hundreds of seabirds near Shetland in the UK due to avian flu, a devastating blow to the local marine ecosystem. It can have major impacts on wild bird populations, leading to the extinction of vulnerable species and changes in subsistence hunting of Indigenous peoples and sports hunting among the broader public.

The Northern gannet, one of the species recently hit by the avian flu outbreak in the Shetlands (Image Credit: Matt McGillivray, CC BY 2.0)

Widespread AI also has the potential to increase the rate of transfer to humans. Zoonotic transmission, the spread between animals and humans, is low. The World Health Organization has reported 860 human infections between 2003-2022 across 19 countries, with 53% of those infections resulting in deaths. Zoonotic transmissions are currently low, but have the potential to increase. 

Looking to the future.

After the 2014-2015 outbreak, agencies, states, and farmers are better equipped to deal with reducing viral spread, which could reduce mortality rates and costs associated with the ‘clean-up’. For instance, in South Dakota, where the 2022 outbreak is currently 3x worse than the 2014-2015 outbreak, businesses are already repopulating flocks, and anticipate that they will be running at normal capacity come September 2022, due to quick mitigation strategies at the onset of this outbreak in 2022 (Sioux Falls Argus Leader). To help reduce future outbreaks, the most recommended preventative measures to implement are biosecurity practices. Structural practices focus on the physical construction and maintenance of facilities, and wildlife management which includes reducing or removing wildlife attractors, preventing access, or adding wildlife deterrents. Operational practices focus on protocols, such as hand washing before and after contact with live birds, cleaning and disinfecting tools or equipment before moving them to a new facility, and wearing disposable boot covers. Biosecurity practices will look different for every facility, and programs like Defend the Flock provide free tools and resources to help create a biosecurity plan. 


Title Image Credit: “Thousands of chickens live in this large place where their main function is to lay eggs.” Carol M. Highsmith (© Rawpixel Ltd., CC0 1.0 Universal)

Jennifer Merems is a writer and researcher focusing on behavioral and nutritional ecology. She is currently a PhD candidate in the Department of Forest and Wildlife Ecology with the University of Wisconsin-Madison. You can learn more about Jennifer by following her on Twitter at @atyourcervid.

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