Avian influenza is a disease caused by viruses known as “influenza type A” which usually infect wild birds (especially wild ducks and geese) and domestic birds. These viruses are almost always transmitted between birds. But, from time to time, one of these viruses is transmitted to humans who then contract what is called bird flu, influenza from birds.

What specialists fear is that one day, a highly pathogenic avian influenza virus will succeed in being transmitted from person to person, resulting in a human-to-human epidemic. For the moment, avian influenza is spread from infected birds to humans, which limits the number of people infected, since few people are in direct contact with birds in the population.

Wild birds are usually only mildly sick when they contract these viruses, if at all. They cause wild bird colds a bit! On the other hand, farmed birds (chickens, turkeys, etc.) are much more vulnerable to these viruses.

Two types of viruses that are sources of influenza avian exist:

– low pathogenic viruses which cause few signs in farmed birds.

– Highly pathogenic viruses which can make farmed birds very sick or kill.

As influenza viruses evolve by mutating, certain pathogenic viruses can cause epidemics in birds, so much so that it is sometimes called “fowl plague” or “chicken ebola”. And sometimes, with some viruses, transmission to humans is more frequent. Thus humans were infected with avian influenza in 1997 (avian influenza virus H5N1, with 6 human deaths) in Hong Kong, in 2003 with the avian influenza virus H7N7 in the Netherlands (a fatal human case), in 2013 with H7N9 avian influenza virus in China. In 2016, there was an epidemic of the H5N8 avian virus in France which did not affect humans, but which is highly pathogenic for farmed birds.

In total, only four avian influenza viruses have ever caused disease in humans: H5N1, H7N3, H7N7 and H9N2.

The most dangerous avian influenza virus known to date has been H5N1.