Influenza virus
Seasonal influenza
Influenza A(H1N1)
Bird flu
Flu pandemic
Influenza virus
How many types of influenza virus are there?
There are three types of flu virus (Influenzavirus): A, B and C. Each of these three types affects humans, except type A, which is the only one to affect both humans and certain animals (birds, pigs, horses and so on). Type A influenza viruses have 16 subtypes H and 9 subtypes N.
Type A viruses regularly infect a large number of people during the winter season, causing a considerable number of deaths around the world. Type B viruses cause relatively serious respiratory ailments. As for type C viruses, they are not considered a cause for concern and are inter alia responsible for very minor respiratory ailments.
What do the letters H and N stand for in the name of the virus?
These are surface antigens of the type A influenza virus which determine the subtypes. Subtypes H (haemagglutinin) are the most important from an epidemiological point of view, since they govern the ability of the virus to settle in cells and to penetrate them where they then multiply. Subtypes N (neuraminidase) determine the release of viruses formed in the cells.
Seasonal influenza
What is seasonal influenza?
Seasonal influenza, a human illness which is rife above all during the winter period, is not to be confused with a cold or a chill. It is a severe respiratory infection caused by different flu viruses (Influenzavirus). The most common symptoms of an influenza without complications are a sudden outbreak of fever, shivering, headaches, muscular pains and a dry cough. The cough may last for a rather long time, but the other symptoms generally disappear in two to seven days. Seasonal influenza is above all dangerous because of the complications it can cause. Those complications essentially involve pneumonia, and occur more frequently among elderly people and those suffering from other chronic illnesses which make them prone to pneumonia. It is possible to protect oneself against seasonal influenza from October by means of vaccination. As the influenza virus is constantly mutating, a new vaccine against seasonal influenza must be developed each year.
Influenza A(H1N1)
What is influenza A(H1N1)?
The influenza A(H1N1) virus is a new human virus resulting from a combination of genes with different origins, porcine, avian and human. This virus was first detected in Mexico in March 2009 and is characterised by human-to-human transmission.
(More information about influenza A(H1N1) under the heading Questions and Answers)
Bird flu
What is bird flu?
Bird flu is an animal illness found throughout the entire world. Identified for the first time in Italy in 1878, bird flu affects all species of wild and domestic birds, but to differing degrees.
Bird flu can also affect other animal species like pigs and cats.
Bird flu is caused by the type A flu virus (Influenzavirus) which has 16 subtypes H and 9 subtypes N. The form of the bird flu virus considered slightly pathogenic only causes minor symptoms and can pass unnoticed. The highly pathogenic form of the virus involves subtypes H5 and H7, and more particularly H5N1, which spreads extremely rapidly and currently involves high mortality among birds and poultry.
In exceptional cases, the subtype H5N1 of the bird flu virus can also be transmitted from animals to humans. The virus is transmitted by air, essentially when there are close, prolonged and repeated contacts in confined spaces with the respiratory secretions or excrement of infected animals, or by exposure to contaminated surfaces or materials.
Flu pandemic
What is a pandemic?
A pandemic is the spread of a human illness on a global scale which rapidly affects all parts of the world and more than 25% of the global population. A pandemic occurs when a new virus appears against which the human immune system has no defence.
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