• What is avian flu?

  It is an infection that affects birds, caused by an influenza virus. It is easily spread, and varies widely: some strains cause little obvious effect while others are usually fatal.

• What does H5N1 mean?

  The flu virus carries two proteins that form spikes on the surface of the virus coating: haemagglutinin (H) and neuraminidase (N). These vary from subtype to subtype. There are fifteen different versions of H and nine of N. So H5N1 is a flu virus characterised by having haemagglutinin 5 and neura-minidase 1.

• What is special about it?

  It is particularly contagious in birds, and deadly. That means that it could potentially spread with speed through poultry flocks, causing huge damage.

• How can this be prevented?

  In the first place, by making sure that domesticated flocks are isolated as far as possible from wild birds. This is difficult to achieve, especially if flocks are free-range and spend a part of their time in the open.

• Isn’t it possible to vaccinate flocks?

  Yes, and this technique has been used, along with slaughter, to control outbreaks in the Far East. But the vaccine takes some weeks to take effect, by which time the disease may have spread so far that vaccination will not be able to stop it. Slaughter is much quicker.

• What other precautions should be taken?

  In China and Vietnam, the movement of domesticated birds was an important cause of the virus spreading. So restricting movements of poultry makes sense. The greatest danger arises if the disease gets a hold in areas where there is a high concentration of domesticated birds.

• But will avian flu transfer to humans?

  With considerable difficulty, yes. Experience so far suggests that the only people likely to catch it are those closely connected to poultry farming. Handling birds, and coming into contact with their droppings, are the principal risks. Birds excrete the virus in faeces which dry out and form dust that can be inhaled.

• What about eating poultry?

  That is perfectly safe so long as the birds are properly cooked. The virus is destroyed at normal cooking temperatures.

• Is avian flu dangerous to humans who catch it?

  Very dangerous. About half the confirmed cases of the disease in humans have proved fatal. But it is possible that there have been many unconfirmed cases, so the true death rate may be lower than that.

• Could it acquire the ability to spread easily in humans?

  The biggest concern. Earlier world epidemics (pandemics) of flu originated in avian flu viruses that mutated to become easily transmissible in humans. In the process, the virus trades virulence for transmissability, becoming far less lethal.

• What is needed to allow this to happen?

  Time, and the close association — perhaps in a single human patient or in an animal such as a pig — of avian and human flu subtypes. Nobody can predict if the deadly mutation will occur, or when. But the more widespread avian flu is, the more likely the mutation is.

• What would the effects be?

  A worldwide spread of a new form of flu to which nobody had any acquired resistance, infecting perhaps a quarter of the world population and killing anything between two million and fifty million.

• Isn’t it rather a leap from a few dead birds in Scotland to millions of people dying?

  Isn’t this just another health scare? It is a big leap, but it has happened before. The 1918-19 pandemic was triggered by an avian strain that mutated, and it killed 20 million (some say 40 million) people. So we know it can happen.

• But that was in 1918. Surely we would be better prepared?

  True, up to a point. We will have stocks of antiviral drugs such as Tamiflu, which may help. But the sheer scale of the infection is likely to overwhelm healthcare facilities. Vaccine production, even if an effective vaccine is ready, is far too limited to protect more than a fraction of the population.

• That’s all a bit theoretical at the moment. More to the point, what should we do if we see a dead bird?

  The Department for the Environment says that if you see a single dead swan or duck, three dead birds of the same species, or five dead birds of different species, you should ring the helpline (08459 335577) to report it. Do not touch the birds, just report the location.

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