Last year marked the beginning of the largest outbreak of high pathogenicity avian influenza (HPAI) in the U.S. This outbreak has led to the deaths of more than 58 million birds, either from infection or culling to prevent further outbreaks. On the West Coast in the last 30 days, there are detected and reported outbreaks of HPAI in one domestic flock in Washington and one commercial flock and three backyard flocks in California.
Avian flu is separated into two main categories based on pathogenicity: high pathogenicity (HP) and low pathogenicity (LP). LP avian influenza (LPAI) occurs in wild waterfowl and shorebirds and does not cause illness. It can also infect domestic poultry, but it will lead to few or no symptoms. HPAI, however, is extremely infectious, with high avian fatality rates. One of the most well known strains of HPAI is H5N1, which was first discovered in China in 1996.
There are three types of avian flu: A, B, and C. Within those types there are many different subtypes or strains. “Usually the strains kind of die out; [they] get interrupted. Enough of the carriers die before the next migration that it just kind of stops. But last year … coming into this year as well, there were actually two different strains operating on the North American continent in one year,” says Oregon State University Extension Wildlife Specialist Dr. Dana Sanchez. Both HPAI H5 and H5N1 were confirmed in North America in 2021 to 2022.
The threat to wild bird populations can be significant. In late December of 2021 in Israel, thousands of common cranes died after contracting avian flu. These cranes pass through Israel on their migratory path to Africa. Local farmers were required to cull approximately one million chickens to prevent the spread of the virus. Eagles in the U.S. are also threatened by H5N1, with HPAI-related mortality confirmed in 136 bald eagles since Jan. 2022. Consuming sick birds and living near water puts birds of prey at risk. According to a Jan. 2023 Scientific Reports article by wildlife disease researchers in Georgia and Florida, “If HP [influenza A virus] persists in North America, the proclivity of bald eagles for nesting near and along bodies of water cohabited by waterfowl may be to their detriment. These observed impacts of HP IAV on bald eagles represent an early horizon scan of an emerging threat to populations of predatory and scavenging birds across North America.”
Sanchez emphasizes the risk of wild to domestic animal transmission: “The transmission is going to be one of opportunity. [Bird] poop can fly in from an over-flying bird and land; or the way a person is feeding [their animal(s)], or housing, their domesticated animals could in fact be allowing wild animals in and out without any real blockage between the movement of those animals or whatever they might be carrying.” Owners of domestic birds, such as a backyard chicken flock, should be taking precautions to protect their animals from infection. They can provide disposable boot covers for anyone having contact with their flock, clean and disinfect tools or equipment before moving them to a new poultry facility, clean and disinfect enclosures and equipment used for their birds, and keep their birds compartmentalized to avoid contact with wild birds. One resource that bird owners can turn to is Defend the Flock, a program within the U.S. Department of Agriculture’s (USDA) Animal and Plant Health Inspection Service. This program provides information about biosecurity and signs of illness for multiple different avian illnesses, including avian influenza.
With both infection and the necessity of culling to prevent further spread, avian flu has impacted the U.S. poultry industry. It remains safe for humans to consume poultry and poultry products, as long as meat is properly cooked and handled hygienically.
Only the influenza A virus type is zoonotic, meaning that it can spread from a non-human to a human and back again. Within these types there are only five known zoonotic subtypes: H5N1, H7N3, H7N7, H7N9, and H9N2. While the Center for Disease Control (CDC) does not consider there to be a high risk to humans from H5N1 or any of the other zoonotic strains, there have been cases of human infection. An 11 year old girl in Cambodia died of avian flu shortly after her diagnosis on Feb. 22, 2023. Her contraction of the virus seems to have occurred through exposure to a chicken, either in a coop near her house or during the processing of the bird. According to the World Health Organization (WHO), there have been a total of 240 human infections with A(H5N1), with a fatality rate of 56 percent as of Feb. 2, 2023. This fatality rate should be taken seriously, but it also must be acknowledged that with a higher rate of transmission in humans, the fatality rate would probably drop.
There are precautions people can take to protect themselves from infection, and the best way to avoid contracting avian flu is to avoid sources of exposure. This means observing birds from a distance and avoiding touching birds, especially sick or dead birds, and surfaces that have been in contact with birds. If in contact with potentially infected birds, the CDC recommends wearing personal protective equipment while in contact with birds, washing your hands after contact, and changing clothes after contact with birds whether or not they seem sick. Getting the seasonal flu vaccine is also advised; according to the CDC, “Seasonal flu vaccination will not prevent infection with bird flu viruses but can reduce the risk of getting sick with human and bird flu viruses at the same time.” In the case of the evolution of a more human to human transmissible strain, there are vaccines currently in development. AUDENZ, a vaccine that targets the H5N1 subtype, is already approved for use by the Food and Drug Administration. In an article for Scientific American, CSL Seqirus, the company that worked with the U.S. Department of Health and Human Services to develop AUDENZ, claims that they “would be able to supply the U.S. government with 150 million doses within the first six months of a pandemic being declared.”
People who become sick within 10 days of exposure to a sick bird are advised by the CDC to isolate until they can get proof that they are not infected and have recovered. According to the CDC, human avian flu symptoms can include fever or feeling feverish, cough, runny nose, sore throat, headache, muscle aches, eye redness, difficulty breathing, shortness of breath, and diarrhea. While rare, human to human transmission is possible and close contacts of an infected person should monitor themselves for any symptoms. Flu antiviral drugs can be used in the case of human infection, but may not be as effective against some avian flu viruses.
In the possibility of an avian flu pandemic, the WHO considers some cause for alarm: “If the H5N1 virus were to change and become easily transmissible from person to person while retaining its capacity to cause severe disease, the consequences for public health could be very serious.” However, the likelihood of this is slim, especially if people do their best to prevent the spread of the virus.
