Influenza - Avian

What is avian influenza?

Avian influenza, commonly known as bird flu, is a contagious viral disease caused by influenza A viruses which primarily infect wild birds and poultry. However, in rare cases, it may also infect humans and mammals.

Human infections with the avian influenza virus have occurred sporadically since its first detection in Hong Kong in 1997. There has been no sustained human-to-human transmission, although several small clusters of infections have been reported.

The avian influenza viruses are divided into several sub-types. The most frequently identified sub-types of avian influenza that have caused the majority of human infections to date are the A(H5N1) and A(H7N9) viruses:

• The A(H5N1) virus is highly contagious in birds and has been associated with severe disease and deaths in humans. Since its widespread re-emergence in 2003, the virus has spread in Asia, Europe, and Africa. It has become endemic in poultry populations in some countries such as China and India. Most human infections occurred after prolonged and close contact with infected poultry. Rare, limited, and non-sustained human-to-human spread of this virus has been reported.

• A multistate outbreak of A(H5N1) virus among dairy cattle herds was reported across the United States in March 2024. The A(H5N1) virus was also detected in udder swabs and raw (unpasteurised) milk samples from infected cows. Farm workers in different farms were infected after their exposure to the infected cows.

• Human infections with H7N9 were first reported in China in 2013. Most human infections had occurred after exposure to infected poultry or live bird markets. Similarly, rare instances of limited, non-sustained human-to-human spread have been reported in China.

Aside from A(H5N1), there have also been sporadic cases of human infection with various subtypes of avian influenza (i.e. H3, H5, H7, H9, H10):

• Sporadic cases of human infections with other avian influenza viruses, including H5N6 and H9N2 viruses, have also been reported in China and other countries. Spread from birds to humans is rare and no human-to-human spread has been reported.

The World Health Organization (WHO) advises that sporadic human cases of avian influenza infection are not unexpected, given that there is a risk for sporadic infections and small clusters of human cases due to exposure to infected poultry or contaminated environments, if avian influenza viruses are circulating in poultry.

How is avian influenza transmitted?

Human infection with avian influenza virus is primarily acquired through:

• Direct or close contact with potentially sick or dead birds and other animals (e.g. mammals)

• Direct exposure to secretions or excretions from infected animals, or their contaminated environment

• Consumption or exposure to infected animals or undercooked or unprocessed animal products

There is currently no evidence to suggest that the virus can be spread through the consumption of properly prepared poultry or eggs, although a few cases have been linked to consumption of dishes containing raw, contaminated poultry blood.

Based on current available evidence, avian influenza viruses have not developed the capability to easily infect humans and other mammals, nor to transmit easily between humans.

The incubation period is typically 1 to 10 days, ranging from 1 to 17 days.

What are the symptoms of avian influenza? 

The signs and symptoms of human infection with avian influenza viruses range from mild respiratory symptoms to severe illnesses such as pneumonia.

The most common symptoms of human infection with avian influenza virus are similar to those of regular flu:

• High fever (usually over 38 degrees Celsius)

• Cough

• Sore throat

• Runny nose

• Phlegm

• Difficulty breathing

• Headaches

• Muscle or body aches

• Fatigue

Other symptoms include:

• Diarrhoea

• Nausea

• Vomiting

• Seizures

• Conjunctivitis

The disease may progress rapidly, leading to respiratory failure with acute respiratory distress syndrome (ARDS), multiorgan failure, and may result in death.

What are the risk factors?

Risk factors include:

• Relevant travel to or residence in areas with recently reported cases of avian influenza in the past 6 months.

• Contact with infected poultry and other animals (e.g. mammals), such as slaughtering, de-feathering, handling or preparing infected birds for consumption may increase the risks of contracting the avian influenza infection.

How is avian influenza treated?

Treatment may vary depending on the symptoms. If the disease is caught early, Tamiflu (Oseltamivir) is often the recommended treatment for the avian influenza virus alongside symptomatic treatment.

How to prevent avian influenza?

To reduce the risk of exposure to avian influenza, travellers to affected areas are advised to maintain their vigilance and adopt the following health precautions:

• Avoid visits to commercial or backyard poultry farms, live bird markets and dairy farms

• Avoid contact with potentially sick or dead birds and animals

• Avoid contact with animal waste or untreated bird feathers

Please refer to Health Advice for Travellers for the full list of precautions to take when travelling.

Note: The seasonal influenza vaccines do not protect against avian influenza infection.