Bird Flu: HPAI H5N1 Explained
Bird Flu: HPAI H5N1 What You Need to Know About Its Risks and Prevention
Highly Pathogenic Avian Influenza, also known as bird flu or H5N1, has recently captured public attention. While primarily spreading among birds and other animals, cases of animal-to-human transmission have raised concerns among health experts.
Informing yourself about this illness is the best thing you can do to combat misinformation, reduce fear, and take appropriate action.
This article explains the basics of bird flu and breaks down common terms used to discuss bird flu infections.
Pathogenicity: What is HPAI?
Pathogenicity is a virus’ ability to infect a person, multiply, and make them sick. The difference between highly pathogenic avian influenza (HPAI) and low pathogenic avian influenza (LPAI) lies in how severe the disease is in birds.
- HPAI: Causes severe illness and high death rates in birds, especially poultry.
- LPAI: Causes mild or no symptoms in birds and is generally less harmful. However, it can potentially mutate into HPAI.
Both types are caused by influenza A viruses but differ in their impact and risks.
Current Clade: 2.3.4.4b
Bird flu clades are groups of related avian influenza viruses classified by their genetic similarities and evolutionary history.
The current clade, 2.3.4.4b, has spread widely among wild birds and poultry across the globe, making it one of the most transmissible clades seen so far.
Unlike earlier clades, 2.3.4.4b has shown an increased ability to infect mammals, which has raised concerns about its potential risks to human and animal health.
Different Variants, Different Symptoms
A variant of bird flu is a version of the virus with small genetic changes that make it slightly different from other versions.
These variants possess small mutations, sometimes called genotypes, which might affect how easily it spreads,
which animals it infects, or how severe the disease is. The two variants making headlines are those with the B3.13 or D1.1 genotypes.
B3.13 Genotype
The B3.13 genotype is found most frequently in dairy cows and has been infecting dairy workers.
While cases may vary in severity, symptoms of B3.13 infections are usually consistent with mild cases of bird flu. Symptoms of mild cases of bird flu include:
- Eye redness and irritation (conjunctivitis)
- Mild fever
- Cough
- Sore throat
- Runny or stuff nose
- Muscle or body aches
- Headaches
- Fatigue
- Less common symptoms include diarrhea, nausea, or vomiting
Respiratory symptoms typically start 2 to 7 days after exposure and are most commonly experienced within 3 days. Eye symptoms like redness and irritation may appear within 1 to 2 days ¹.
D1.1 Genotype
The D1.1 genotype is found most frequently in poultry and wild birds like geese. While cases may vary in severity, symptoms of D1.1 infections are generally more consistent with moderate or severe cases of bird flu.
Symptoms of moderate or severe cases of bird flu may include:
- Symptoms listed above that limit or prevent usual activity
- High fever
- Shortness of breath or difficulty breathing
- Altered consciousness
- Seizures
Complications can occur from bird flu infections ¹. These complications include but are not limited to:
- Pneumonia
- Respiratory failure
- Acute respiratory distress syndrome
- Acute kidney injury
- Multi-organ failure (respiratory and kidney failure)
- Sepsis, septic shock
- Inflammation of the brain
Current Status
There are no cases of human-to-human transmission. Bird flu is spreading by animal-to-human transmission, through farm work or other close contact with animals including chickens on backyard poultry farms.
It can also be transmitted to humans by wild animals like waterfowl such as ducks or geese. A wild or domestic animal (such as a cat) can become infected by consuming infected material and can then potentially infect humans.
Why is this a risk to our health?
Every new infection of bird flu in people increases the potential for the virus to change (mutate). Flu season is an especially dangerous time, because flu viruses can undergo reassortment.
This means that they can easily exchange pieces and create new versions of flu virus. Bird flu has the potential to reassort with seasonal flu.
The reassortment has the potential to better infect humans or cause human-to-human transmission.
What you can do
The best way to prevent H5 bird flu is to avoid exposure whenever possible ². Infected birds shed avian influenza A viruses in their saliva, mucous, and feces.
Other infected animals may shed avian influenza A viruses in respiratory secretions and other bodily fluids (e.g., in unpasteurized cow milk or ‘raw milk’).
- Wild birds can be infected even if they don’t look sick. Avoid contact with sick or dead animals, especially wild birds or poultry.
- Wear recommended personal protective equipment (PPE) when in direct or close contact with wild birds, sick or dead poultry, or other animals.
- Avoid touching surfaces or materials (such as animal litter or bedding) that have been contaminated with body fluids from wild birds, poultry, or any animals with confirmed or suspected infection.
- Do not consume raw milk or unpasteurized milk products. Similarly, do not feed these or raw meat products to pets or other animals.
For people with backyard poultry flocks or others with close contact to animals (such as hunters), more measures may be necessary to prevent infections. See the USDA’s website for best prevention practices.
HNL Lab Medicine
The current risk to the general public is low. If you’re experiencing respiratory symptoms such as fever, cough, or shortness of breath, it’s important to determine the cause, especially during flu season or amid ongoing COVID-19 risks. Bird flu infections will test positive on influenza A tests, and samples will then be sent to a special lab for confirmation and genomic sequencing when appropriate.
Visit your provider to discuss your symptoms and to get the diagnostic tests that are most appropriate for you. Don’t forget to visit one of our many Patient Service Centers to complete your lab work.
HNL Lab Medicine will continue to monitor the situation and provide updates if necessary. We are dedicated to supporting public health by providing accurate, timely diagnostic insights and fostering awareness about emerging health concerns like bird flu.
REFERENCES
¹ Centers for Disease Control and Prevention. (2024, December 20). Signs and symptoms of bird flu in people. U.S. Department of Health and Human Services. https://www.cdc.gov/bird-flu/signs-symptoms/index.html.
² Centers for Disease Control and Prevention. (2024, July 19). Prevention and antiviral treatment of avian influenza a viruses in people. U.S. Department of Health and Human Services. https://www.cdc.gov/bird-flu/prevention/index.html.