Avian Flu (Bird Flu): All You Need To Know

Avian flu is caused by avian influenza A viruses that primarily affect birds. They are members of the Orthomyxoviridae family of viruses. Ducks, geese, swans, and other waterfowl are usually the primary hosts. Feces from an infected bird can spread the disease to other birds.

Apart from birds, cats, dogs, pigs, and horses have been known to contract the avian flu, but the risk is very low [3].

There are two types of the bird flu virus:

•   Low pathogenicity avian influenza (LPAI): which causes only mild symptoms of the disease, and
•   Highly pathogenic avian influenza (HPAI): meaning it can cause severe illness or symptoms and even death. HPAI is also known as the ‘fowl plague.’

The more virulent forms are believed to be mutations of the milder versions.

Though rare, the avian flu can spread to humans. Once infected, a human cannot transmit the virus easily to another person. Most people infected by the avian influenza virus have had prolonged close contact with infected birds. They either breathe in droplets of air or touch their mouths, eyes, or nose after touching surfaces with the virus on them.

Though infections in humans are rare, avian influenza viruses can cause deaths. For this reason, outbreaks are closely monitored. There is also a risk of a new mutation being highly transmissible among humans, leading to a future pandemic.

Specific variants of the avian influenza virus, such as H5N1, H7N9, H5N6, H5N8, and newer strains, are causes of concern. H7N9 does not affect birds but infects humans. H5N1 is of particular interest based on the number of outbreaks it triggers, including the recent 2021-2022 wave [8].

The avian flu can be deadly, but timely medical intervention can help minimize the severity and prevent deaths.

According to the CDC, it is safe to eat cooked poultry or eggs if prepared hygienically and cooked thoroughly. Food safety guidelines must be followed when handling raw poultry to prevent salmonella and other infections. 

In the United States, if you work with live chickens, you will need to follow USDA food safety guidelines.

According to the GIDEON database of infectious diseases, the first recorded cases of bird flu in humans were from Hong Kong in 1997. There were 18 cases, of which six were fatal. From 2003 to 2016, the World Health Organization (WHO) recorded 850 infections from the H5N1 bird flu subtype.

This number may not seem high compared to other diseases, but more than half of the infected individuals died. The majority of human deaths from the bird flu during this time were recorded in Egypt, Indonesia, and Vietnam.

2003: Thousands of chickens were culled in the Netherlands during an avian influenza outbreak by an H7N7 strain. One human death was reported.

2013: Dozens of H7N7-related human deaths were recorded in China.

2014: In the Americas, the first human infection with HPAI H5N1 was in Canada.

2020-2025: Global Multi-Country Outbreak

Since 2020, a major H5N1 outbreak has affected multiple countries across every continent except Australia. The outbreak involves primarily H5N1 clade 2.3.4.4b, which first spread across Europe in autumn 2020 before spreading to Africa and Asia. In February 2022, the United States reported its first HPAI H5N1 detection in commercial poultry since 2020, marking the beginning of widespread outbreaks in North America.

Between December 2023 and March 2024, HPAI A(H5) outbreaks were reported in domestic (227) and wild (414) birds across 26 countries in Europe. The outbreak has also affected mammals, with H5N1 detected in over 50 mammal species, including seals, sea lions, and foxes. In December 2023, HPAI A(H5N1) virus infections were reported in elephant and fur seals in the Antarctic, marking the first time the virus reached both polar regions.

2023-2025: Cambodia Outbreak

Cambodia experienced a resurgence of human H5N1 cases beginning in February 2023, after nearly a decade without reported human cases.

Between January and July 2025, Cambodian health authorities reported 12 laboratory-confirmed cases of human infection with avian influenza A(H5N1), including 6 fatalities.

Since 2023, Cambodia has reported 28 human cases total, with a case fatality rate of approximately 43%.

All human cases have been linked to direct contact with infected or dead poultry, with no evidence of sustained human-to-human transmission.

According to the CDC, symptoms can range from mild to severe. They include:

• Conjunctivitis
• Flu-like symptoms (fever, headache, cough, nasal congestion, sore throat, muscle pain)
• Occasionally, nausea, vomiting, diarrhea, severe respiratory illness, pneumonia, and even multi-organ failure in severe cases.  

Symptoms can persist for up to two weeks, but most last two to seven days.

Duration of Illness

Symptoms can persist for up to two weeks, but most last two to seven days.

Since avian flu symptoms can be similar to that of other influenza viruses, and some patients may present with co-infections like pneumonia, lab testing is required for accurate diagnosis. According to the CDC, tests are more accurate if tissue samples are collected within the first few days of illness.

WHO recommends an RT-PCR (reverse transcriptase-polymerase chain reaction) test or a real-time reverse transcriptase PCR assay. Other tests used are rapid antigen tests.

Avian influenza in humans can turn into a severe illness and must be treated in a hospital. WHO notes that the antiviral medicine, Oseltamivir, can reduce disease severity and prevent death. Zanamivir, delivered through an inhaler, can also be an alternative. In recent times, oseltamivir resistance has been detected.

There is no commercially available vaccine for the bird flu. In 2007, the US FDA approved a vaccine to protect humans against one type of H5N1 virus. It can be used in adults (18-64 years of age) at increased risk of exposure to the H5N1 virus. The US Federal Government stockpiled this vaccine in the event of rapid human-to-human transmission.

The CDC notes that the best prevention is to avoid sources of exposure.

Frequent hand washing with warm water and soap is recommended before and after handling raw poultry. You may also use separate utensils for raw meat. Ensure you cook your chickens and eggs thoroughly before eating and avoid contact with wild birds and poultry.

If it is your job to work with wild birds or poultry, wear protective gear and ensure you clean your hands before touching your eyes, nose, or mouth [9].

One of the biggest challenges in developing a bird flu vaccine, even for birds, is the many different varieties of the avian influenza virus. There are also new mutations and strains of the virus to continue tackling, like with the human flu.

The bottom line is that there is no need to panic about a bird flu epidemic or pandemic in humans. The risk of transmission to humans and between humans is still very low.

However, public health officials and researchers must remain vigilant and track the raging bird flu outbreaks occurring across the world to protect our wildlife and poultry.

More data-driven studies are required to determine levels of risk to birds, animals, and humans. Researchers may use comprehensive platforms like the GIDEON infectious disease database for unified data on infectious diseases.