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Science

A never-ending story: bird flu strikes again

Authorities in southern Germany have discovered the H5N2 bird flu virus on a poultry farm. Around 13,000 animals will have to be killed. Here's an overview of the virus and its dangers.

What is bird flu?

Avian influenza - also called bird flu or fowl plague - is a viral disease that infects birds, especially wild geese and ducks. It can spread easily among domestic poultry like chicken and turkeys and if they contract more serious forms of the virus most animals will die of bird flu. That's why many virus types are considered “highly pathogenic."

Which viruses cause bird flu?

Several strains of viruses can be responsible. They all belong to the group of influenza A viruses. The most highly pathogenic and most commonly-known strain is H5N1. Another example is H7N9. But any influenza A virus may cause bird flu - it only has to adapt itself to birds as a host. Dozens of bird-infecting influenza virus variants are known. Their names range from H1N1 to H15N9.

What do H and N stand for?

a flu virus Photo: Novartis Vaccines

An influenza virus

Influenza viruses carry proteins on their surface. H stands for hemagglutinin, it binds the virus to cells in the respiratory tract, for example. N is the abbreviation for neuraminidase, a protein that is required for virus replication.

These proteins vary in their composition and structure. The different types are identified by different numbers.

Can bird flu viruses infect humans?

Most avian influenza viruses do not infect humans; but some, however, can. The only subtypes known to be able to cross the species barrier to humans are H5N1 and H7N9. These can cause serious infections in people.

Such cases might occurr in people who had contact with sick or dead poultry that were infected with these viruses. Unlike other types of flu, H5N1 and H7N9 usually do not spread between people.

If someone is infected with an avian influenza strain, the illness is unusually aggressive. Fatalities are high: about 60 percent of people infected with the virus have died from their illness.

When and where did severe bird flu outbreaks begin?

Avian flu outbreaks caused by non-human infecting subtypes occur quite often.

In 1997, the H5N1 virus first infected humans during an outbreak among poultry in Hong Kong. Since then, dozens of countries in Asia, Africa and Europe have reported H5N1 outbreaks. In 2014, the US also reported an outbreak of the virus.

Several hundred people have been infected worldwide. According to the World Health Organization, more than four hundred people died from bird flu. Most of these deaths occurred in Egypt and Indonesia.

The H7N9 subtype first infected humans in China in March 2013.

Bird Flu in Hong Kong 2014 Photo: REUTERS/Tyrone Siu

If bird flu is detected, the culling of poultry has to begin immediately

Why do authorities worry so much when bird flu breaks out?

Bird flu is highly contagious, it spreads very quickly. When migratory birds get infected, they can carry the disease to other parts of the world. Even if the strain does not infect humans, avian flu is can be disastrous: outbreaks kill thousands of animals at a time and impacts the livelihoods of many people, local and national economies and international trade. There is always the danger that the virus will quickly mutate. It might adapt to humans and be even more deadly.

What is the difference between bird flu and swine flu?

Swine flu is caused by influenza A or C virus variants, the most common being H1N1. The respiratory system of pigs is quite similar to that of humans - that's why swine flu viruses can infect humans more easily than avian flu viruses. Swine influenza viruses caused a pandemic in humans in 2009.

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