Tiny quick-change artists

Dr. Andrea Bannert has been with since 2013. The doctor of biology and medicine editor initially carried out research in microbiology and is the team's expert on the tiny things: bacteria, viruses, molecules and genes. She also works as a freelancer for Bayerischer Rundfunk and various science magazines and writes fantasy novels and children's stories.

More about the experts All content is checked by medical journalists.

A new flu pathogen is making headlines again: H5N8. Is it also dangerous for humans?

A new avian flu virus is currently making headlines in the media: H5N8. It was first discovered in a teal on Rügen as part of a wild bird surveillance. Some people's heads are spinning at the constant new virus variants. What different flu viruses are there? How dangerous are they really? And why can't the influenza pathogens just be eradicated, such as smallpox?

Altogether there are three different types of flu virus: A, B and C. But only influenza A viruses can be really dangerous to humans. Unlike the B viruses, which usually only provoke milder disease processes, and the C viruses, which only appear very sporadically, they are responsible for the severe flu epidemics. They are very versatile and are divided into a number of subgroups.

Grappling hooks and escape helpers

These subgroups are divided according to the proteins that sit like spikes on the surface of the spherical pathogen. The influenza viruses need these to attack human cells. H stands for hemagglutinin - these are the grappling hooks with which the viruses attach themselves to the host cell. After the virus has multiplied thousands of times in them, the neuraminidase (N) helps the newly created viruses to leave the sinking ship again.

16 different hemagglutinins (H1 to H16) and nine different neuraminidases (N1 to N9) are known in influenza A viruses. In theory, any combination is conceivable, i.e. a total of 144 different subtypes. In the preferred host of influenza A viruses, birds, all known H and N subtypes have also been detected. Ten different subtypes have affected humans so far. However, viruses of the same subtype can also be dangerous to different degrees, depending on how easily they are transmitted and how aggressive they are. The largest outbreaks in each case:

• A / H1N1: Spanish and Russian flu
  This virus subtype triggered the devastating Spanish flu, which claimed an estimated 50 million lives between 1918 and 1920. The exact virus in question could later be reconstructed using virus gene fragments in the lung tissue of the victims. There was another major H1N1 wave in 1977, originating in Russia, but it was less aggressive. In the 2009/10 flu season, numerous people in Mexico contracted another variant of the virus. A / H1N1 is also expected in the current flu season - but in a far less dangerous form than at the beginning of the last century.
• A / H2N2: Asian flu
  A global outbreak of this virus subtype occurred in 1957, killing an estimated one to two million people.
• A / H3N2: Hong Kong flu
  It was the last major flu pandemic. Between 800,000 and two million people died of it between 1968 and 1970. In Germany, it claimed around 30,000 victims. A variant of this subtype is also expected in the current flu season.
• A / H5N1: Avian Influenza 2003
  In 2003, several hundred people died from the so-called bird flu. Most of them were people in Asia who lived in close contact with their poultry.
• A / H7N2: outbreak in the United States
  This virus subtype was first detected in humans in the USA in 2002. Since then it has appeared in several individual cases. The virus is not overly aggressive in humans.
• A / H7N3: mild flu
  H7N3 also produces only mild symptoms. In 2004, the virus was detected in several turkey farms in British Columbia. Two people became infected.
• A / H7N7: infections in the Netherlands
  This virus appeared in the Netherlands in 2003. 89 people became infected, one of them died.
• A / H7N9: 2013 Avian Flu
  After coming into contact with infected poultry, people contracted the H7N9 bird flu virus in 2013. Several people died from severe pneumonia.
• A / H9N2: Rarely affects humans
  This virus has only been discovered in humans in three cases in Hong Kong and China (1999/2003).
• A / H10N8: So far only two infections
  This subtype has so far been found mainly in poultry and migratory birds in southern China. In 2013, however, two people in southern China became infected.

Evolution in time lapse

So there are always new subtypes emerging that are also dangerous for humans. The reason: the influenza viruses can change at record speed. They are a million times faster than mammals. Five years of virus development roughly correspond to the evolutionary changes that separate us from our common ancestors with the chimpanzees. Our immune system therefore has no chance of adapting to the flu viruses quickly enough. And for this reason they cannot simply be exterminated. But how do the viruses do it?

When human body cells divide, a sophisticated repair system ensures that as few errors as possible occur when the genetic information is reproduced. Not so with the influenza viruses. Because with them the so-called mutations are absolutely desirable. The reason: In this way, the viruses can repeatedly outsmart their host's immune system. If this already knows the hemagglutinins of the virus, it forms antibodies for defense. But even with a slight change in the virus surface proteins, this tailor-made firewall no longer works.

Exchanged gene snippets

In addition, the viruses can exchange DNA fragments with one another. At least when two related viruses have infected a cell at the same time. Such new combinations can lead to new virus subtypes. This mechanism is known as an antigen shift. Bird flu viruses can become infectious for humans, especially in pigs. Because the animals are attacked by both human and bird flu viruses. The 2009 H1N1 virus resulted from several such antigen shifts and contains gene segments from avian, Eurasian swine, North American swine and human influenza viruses.

A new vaccine every winter

The constant sapling-swap game of the flu virus makes it extremely difficult to produce suitable vaccines. Since new variants are regularly created, the vaccine against seasonal influenza has to be adjusted every winter. This is always a mixture of different flu viruses that are common at the appropriate time.For the 2014/15 season the components are the same as last year: Influenza A (H1N1) component, Influenza A (H3N2) component and Influenza B component.

The new bird flu virus H5N8 does not pose any acute danger. Experts consider transmission to humans to be unlikely at the moment. That could change - if the virus mutates accordingly.

Tags:  travel medicine toadstool poison plants foot care