What is bird flu called?
The so-called “influenza” viruses are grouped into three strains: types A, B, and C, long since familiar to us. The first – and the commonest – can be divided into fifteen H subtypes and nine N subtypes, depending on the molecules which make up the outer membrane of the virus. The H5N1 variety, present in Asia since the end of December, 2003, is pathogenic to birds. “All the Type-A influenza viruses, including those regularly found to cause seasonal epidemics in man, are genetically unstable and well adapted to evading their hosts’ immune defence systems”, explains the World Health Organisation (WHO). This instability is characterised by an antigenic “drift”, which impedes protection against the virus. How is the virus propagated? This is without doubt the question that raises the most uncertainties. The most obvious culprits are migratory birds, suspected by some people of being able to carry the virus over great distances without becoming diseased themselves. They are then presumed t
