Why Humans Cannot Spread And Catch Bird Flu Easily

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Main Category: Bird Flu / Avian Flu
Also Included In: Biology / Biochemistry;  Respiratory / Asthma;  Infectious Diseases / Bacteria / Viruses
Article Date: 23 Mar 2006 - 14:00 PDT

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The H5N1 bird flu virus strain does not settle in the upper respiratory tract, like the human flu virus does. H5N1 settles in cells deep within the lungs (deep down). This gives us humans two advantages:

1. If I have bird flu and sneeze, hardly any viruses will be sent out because they are deep down in my lungs. With the normal human flu virus, which settles in the upper respiratory tract (nearer my throat), a sneeze will send viruses out in the air and infect people around me.

2. If the virus needs to settle deep down in my lungs before making me ill, I need to be in an environment where lots of them are around me. Huge clusters of H5N1 viruses need to be around me for some of them to have a chance of getting way deep down into my lungs. Basically, I have to surround myself with lots of sick birds and stay very close to them for a long time.

To recap: Humans need lots of bird flu viruses around them to get ill. Infected humans expel tiny amounts of the virus.

This news explains why humans cannot catch bird flu from birds easily, and cannot spread it to other humans (unless you are next to a sick person all day - even then the chances are very remote). Hundreds of millions of birds have died as a result of H5N1 infection since 2003, but only 103 humans.

A study explaining this in detail can be read in the March 23 issue of Nature. It was carried out by researchers at the University of Wisconsin and the University of Tokyo.

The part of the lung the H5N1 virus strain infects is a tough-to-access region. It will not bind to cells in the upper respiratory tract.

This also explains why the death rate for the few people who have been infected is so high. The infection starts so deep inside their lungs.

A study carried out by scientists at the University of Rotterdam, Holland, has come to the same conclusion - you can read about this one in the journal 'Science' (March 24 issue).

The H5N1 virus can mutate in many different ways, one of which is to change so that it starts infecting the upper respiratory tract. This would make it more transmissible among humans. However, if this happened, it would also be easier to treat as infection would not start deep down in the lung.

This could also explain why some people have developed antibodies against H5N1 but had not got ill. The virus probably entered their bodies, but did not manage to get deep down into their lungs.

Many scientists have written to Medical News Today saying that they believe the H5N1 virus will mutate. However, most think the chances of a mutated virus being as deadly to infected humans as the present one are extremely small.

Written by: Christian Nordqvist
Editor: Medical News Today
Copyright: Medical News Today
Not to be reproduced without permission of Medical News Today