Vetstoria

The avian flu virus is able to transform itself over time. This happens through a process of mutation. 2 types of mutation may occur. They are called antigenic drift and antigenic shift.

Antigenic drift: the explanation for annual flu vaccination in humans

Antigenic drift is a process by which the virus modifies slightly its surface glycoproteins H and N.

The flu virus is coated with glycoproteins. Our immune system may be presented with this material through infection or vaccination. It is going to memorise the virus special structure and get ready for further infection from the same agent.

Antigenic drift = Virus ability to create slight changes in its coating

If this happens, the immune system:

• Will be fooled by this slightly different virus
• Not going to recognise it well
• Will not protect against the effects of the virus

With the antigenic drift, the flu virus changes all the time. Therefore the way we can protect ourselves is by getting vaccinated every year.

How does that work?

• WHO collects information about the newly emerging strains of flu virus
• At a given date, the information is given to the laboratories which produce flu vaccine
• Production of flu vaccine different every year
• Adapted and effective if WHO’s predictions are correct

Antigenic shift: the trigger of a pandemic

Antigenic shift = Virus ability to changes dramatically its surface proteins to produce an altogether new virus

• Antigenic drift occurs in both the influenza A and B
• Antigenic shift is possible only for influenza A

This is because it infects more than just humans: allows the meeting of 2 different flu viruses

Men and pigs commonly get infected by the classic seasonal flu virus. Should an infected individual get in contact with the avian flu virus, it is possible that the 2 different viruses meet. If so they may combine to form a new type of virus. If the recombinant virus is produced in the pig first, it may then be transmitted to humans afterwards and this is precisely what happened for the 3 flu pandemics that occurred last century.

The new virus:

• Mixture of the surface glycoproteins of the two original strain
• Completely different virus with new characteristics
• Evade completely our immune system

The risk brought by the antigenic shift is the production of a new virus with different properties. While today’s avian flu virus is not very contagious to humans, its recombinant with a human flu virus may become very contagious.

The 3 conditions for a pandemic may therefore be achieved:

• New virus
• Very aggressive
• Contagious to humans

This is precisely what we have got to avoid for as long as possible.

The last century has seen 3 pandemics named the Spanish, Asian and Hong Kong Flu.

It is believed that, for all 3, the disease went from a bird to a pig before affecting humans.

In 1918, it is thought that half of the world population got infected with the Spanish flu. This represents about 1 billion individuals. It is likely that the virus killed 50 millions and therefore killed more than the First World War which finished the same year. Along with the black plague, this is one of the worst pandemic to have ever affected mankind.