Bird flu, also known as avian influenza, is a viral infection that can spread between birds and other animals. There are many different strains of bird flu virus. Most bird flu strains only infect birds and do not cause illness in humans. However, some strains, such as H5N1 and H7N9, have caused serious illness and death in people.
How is bird flu spread between birds?
Wild birds like ducks and geese are natural carriers of bird flu viruses. These birds often don’t get sick from the viruses. But they can pass them to domestic poultry, like chickens and turkeys. Bird flu spreads easily between birds through contact with infected birds’ droppings, mucus or saliva. Sick birds also shed virus particles in their feathers and eggs.
Bird flu outbreaks often start when wild, infected waterfowl share areas and water with domestic flocks. From there, the virus can quickly spread between farms. An infected flock can release large amounts of virus into the environment through saliva, nasal secretions, feces and feathers.
Can people get bird flu from eating eggs?
The risk of getting bird flu from eating properly handled and cooked eggs is extremely low. There are a few reasons for this:
- Few bird flu viruses infect chickens raised for eggs
- The virus is mainly found in a bird’s respiratory tract and is shed through saliva, mucus and feces, not eggs
- Commercial egg-handling practices destroy the virus
- Proper cooking kills the virus
Let’s look at these points in more detail.
Few egg-laying flocks get infected
Very few birds infected with bird flu are egg-laying hens. Egg-laying chickens are raised separately from poultry bred for meat. They usually don’t come into contact with wild waterfowl, so have less exposure to bird flu.
It’s more common for bird flu outbreaks to hit broiler chickens (raised for meat) and turkeys. These birds are typically allowed outdoors where they can mix with wild waterfowl. So far, no bird flu outbreaks have originated in commercial flocks of laying hens in the U.S.
Virus is found mainly in respiratory tract, not eggs
Even if laying hens get infected, the virus is unlikely to contaminate the inside of eggs:
- The virus replicates mostly in the respiratory tract (lungs, trachea, nasal passages)
- Virus particles are shed mainly in saliva, mucus and feces, not internally into eggs
- Blood and ovaries usually test negative for the virus
Research on the H5N2 bird flu outbreak in the U.S. in 2015 found no virus traces in the ovaries or eggs from infected hens. Other studies of H5N1 virus in infected ducks also found no virus traces inside eggs.
Egg handling destroys the virus
Even if an infected hen sheds virus internally into yolks or whites, commercial egg handling processes would destroy it:
- Washing – Eggs are washed in hot water up to 120°F to remove dirt and debris. This kills viruses on the shell.
- Sanitizing – Eggs are sprayed with a sanitizing solution. This further reduces any viruses.
- Refrigeration – Eggs are refrigerated at 40°F within 36 hours. This prevents any viral replication.
- Pasteurization – Liquid eggs products are pasteurized by heating to 130-140°F for 3.5 minutes. This kills any possible viruses.
Cooking eggs destroys the virus
Proper cooking provides the final step to destroying any possible bird flu viruses:
- Raw and undercooked eggs may pose a salmonella risk, but not a bird flu risk.
- Cooking eggs until the whites and yolks are solid (160°F) kills all viruses and bacteria.
- Casseroles, sauces, baked goods and other dishes made with properly cooked eggs are completely safe.
As an extra precaution, the FDA requires pasteurized eggs in any products containing raw or undercooked eggs, like cake batter.
Has anyone ever gotten bird flu from eggs?
There are no reported cases of people contracting bird flu viruses from eating eggs or egg products.
Researchers tested supermarket eggs during a large H5N2 outbreak in chickens in the midwestern U.S. in 2015. No traces of viable virus were found internally or on the shell surface of eggs from infected flocks. The results suggest eggs were not contaminated even from infected hens.
During the outbreak, the CDC maintained that properly cooked eggs were safe to eat. There were no cases traced to eggs.
No transmission to humans through eggs or egg products has been reported in any other bird flu epidemics worldwide.
When can bird flu be inside eggs?
While extremely rare, some research shows it may be possible for bird flu virus to replicate inside the reproductive tract and be deposited internally into eggs:
- One study found H5N1 virus in the ovaries and oviducts of infected ducks
- Another found small traces of H5N1 RNA, but no viable virus, inside some eggs from infected ducks
The study authors felt the public health risk from virus traces in eggs was very low. The virus did not grow well in eggs and inoculation studies did not produce infection. More research is needed.
It’s likely eggs could contain virus traces if:
- The laying flock is infected with a strain of bird flu that can replicate internally
- No preventive measures are taken to contain the outbreak
- Infected eggs enter the human food supply
However, this scenario remains very unlikely due to the safeguards in place at hen farms and during egg processing and distribution.
What is the takeaway?
Eating properly handled, cooked eggs does not pose a risk for bird flu infection. Here are some key points to keep in mind:
- Commercial laying hens are at very low risk of infection
- The virus is found mostly in respiratory tracts, not inside eggs
- Egg processing destroys viruses present on shells
- Pasteurization kills any viruses in liquid egg products
- Proper cooking kills any viruses
There are no proven cases of people getting bird flu from eggs. You can continue to safely enjoy eggs and foods made with eggs if they are handled properly and cooked thoroughly.
Conclusion
In summary, the risk of contracting bird flu from eating eggs or products containing eggs is extremely low. Commercial egg production, processing and cooking procedures effectively prevent transmission of bird flu viruses. There have been no reported cases of humans contracting bird flu from eggs. As long as eggs are properly handled and cooked, they can be enjoyed safely without worry of bird flu infection.