Avian influenza

What is Avian influenza?

Avian influenza, commonly known as bird flu, is a contagious viral disease caused by influenza A viruses which primarily infects wild birds and poultry. However, in rare cases, it may also infect humans and mammals. In particular, the A(H5N1) and A(H7N9) viruses have been known to cause majority of human infections to date. 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).

Human infections with the avian influenza virus are rare but 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 human infections are the H5N1 and the 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 from Asia to Europe and Africa, and has become endemic in poultry populations in some countries such as China and India. Most human infections have occurred after prolonged and close contact with infected poultry. Rare, limited and non-sustained person-to-person spread of this virus had been reported.

• A multistate outbreak of A(H5N1) virus among dairy cattle herds was reported across the United States (US) in March 2024. The A(H5N1) virus was also detected in udder swabs and raw (unpasteurised) milk samples from infected cows. Three human cases among 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 person-to-person spread have been reported in China.

• 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 person-to-person 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, as long as Avian influenza viruses are circulating in poultry.

What are the symptoms of Avian influenza?

The most common symptoms of human infection with avian influenza 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 possible symptoms include:

• Diarrhoea

• Nausea

• Vomiting

• Seizures

• Conjunctivitis

What are the potential complications 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 disease may progress rapidly, leading to respiratory failure with acute respiratory distress syndrome (ARDS) and multiple organ failure, and may result in death.

How does Avian influenza spread?

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’ undercooked or unprocessed animal products (e.g. unpasteurized milk).

Slaughtering, de-feathering, handling or preparing infected birds for consumption may increase the risks of contracting the avian influenza infection.

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 about 1 to 10 days.

How do I prevent Avian influenza infection?

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

• Observe and practise good personal hygiene at all times.

• Wash your hands regularly with soap, especially before handling food or eating, after going to the toilet, or when hands are dirty from coughing or sneezing. If water is not available, use an alcohol-based hand sanitiser that contains at least 60% alcohol.

• Avoid close contact with persons who are unwell or have symptoms of infectious diseases.

• Cover your mouth with a tissue when coughing or sneezing, and dispose the soiled tissue into the bin immediately. Avoid touching your face, including eyes, nose and mouth with unwashed hands after coughing or sneezing.

• Eat food that have been fully cooked and wash fruits and vegetables before eating them. Avoid eating raw or undercooked meat and seafood, milk/milk products, and food prepared in unhygienic conditions.

• 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.

• Wash your hands thoroughly with soap and water after handling live or dead poultry and birds.

• Wear a mask and seek medical attention promptly if you become unwell or develop respiratory symptoms such as cough or runny nose, and inform the doctor of your travel history.

How is Avian influenza treated?

Treatment may vary, depending on your symptoms. If the disease is caught early, Tamiflu (Oseltamivir) is often the recommended treatment alongside symptomatic treatment. Tamiflu may also be offered to any family members who have been exposed to the virus as (prevention) prophylaxis.

There is currently no vaccine available for humans, and the seasonal influenza vaccines do not protect against avian influenza infection.