According to the antigenicity classification of nucleoprotein, the avian influenza virus belongs to influenzavirus A.

Influenza A virus is classified into several subtypes based on the antigenicity of hemagglutinin (H) and neuraminidase (N) located on its mantle, with 17 subtypes of H and 9 subtypes of N. In theory, 153 subspecies may appear after gene recombination (17x9 = 153). The human pandemics of the century include:

• Spanish influenza caused by H1N1 during World War I and swine influenza in 2009
• Asian influenza caused by H2N2 in the 1950s
• Influenza in Hong Kong caused by H3N2 in the 1960s
• Global influenza caused by H5N1 at the beginning of this century

What is Avian Influenza?

Avian influenza is a disease caused by influenza A virus. It mainly affects birds, but some subtypes, such as H5N1 and H9N2, can also infect humans.

Early symptoms of avian influenza in humans are similar to those of common influenza, including fever, headache, muscle pain, runny nose, sore throat and cough. However, avian influenza is more likely to cause fever, pneumonia, respiratory failure, multiple organ failure and even death. Elderly, children, or chronic patients are more likely to have complications, such as bronchitis and pneumonia.

How does Avian Influenza Spread?

Human beings are usually infected by contact with live birds with avian influenza viruses. Although humans can also be infected by contact with patients, the ability of avian influenza virus to spread among humans is still very low.

All influenza A virus subtypes can infect birds. In birds, the highly pathogenic subtypes are H5 (e.g. H5N2), H7 (e.g. H7N3, H7N7), H9 (e.g. H9N2).

Avian influenza can be classified into low pathogenic avian influenza (LPAI) and high pathogenic avian influenza (HPAI) based on different toxicity in poultry populations. H5 and H7 subtypes are found in both "high pathogenicity" and "low pathogenicity", while H9 subtypes are only found in low pathogenicity. Low pathogenic avian influenza can cause mild respiratory symptoms, reduced food intake, decreased egg production and sporadic death in birds. Highly pathogenic avian influenza is the most serious, with high morbidity and mortality. Infected chickens often die entirely.

Influenza A virus usually infects only one species, but sometimes it can infect another and cause disease. For example, before 1997, the swine influenza virus in the United States was H1N1. However, in 1997, the human H3N2 virus began to cause infection in pigs. Recently, the horse H3N8 virus caused an outbreak in dogs.

How to Prevent Avian Influenza

• Do not visit birdhouses, farms or live poultry markets. Do not feed white pigeons, wild birds, etc.
• Avoid contact with live birds and poultry and their droppings as they may carry the virus.
• Wash hands with soap and water immediately after contact with live birds.
• If you have flu symptoms, see a doctor immediately and wear a mask to prevent spreading the disease to others.
• Cook poultry and eggs thoroughly before eating.
• Build up resistance: get enough sleep and rest, reduce stress, eat a balanced diet, exercise properly, improve indoor air circulation, and do not smoke.
• Avoid going to crowded and poorly ventilated public places.
• When you return, if you have fever or respiratory symptoms, wear a mask and consult a physician and tell him or her where you have been recently.