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2007-11-14 Science & Technology
Outbreak of lethal bird flu confirmed in Britain
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Posted by anonymous5089 2007-11-14 12:29|| E-Mail|| Front Page|| [694 views ]  Top

#1 A useful explanation to those not familiar with flu types.

HPAI A(H5N1) is the technical name for Avian flu. It means "highly pathogenic avian influenza virus of type A of subtype H5N1". However, from there it is described to include its sub-sub type, for example:

A/chicken/Nakorn-Patom/Thailand/CU-K2/04(H5N1):

* A stands for the species of influenza (A, B or C).
* chicken is the species the isolate was found in.
* Nakorn-Patom/Thailand is the place this specific virus was isolated.
* CU-K2 identifies it from other influenza viruses isolated at the same place.
* 04 represents the year 2004
* H5 stands for the fifth of several known types of the protein hemagglutinin.
* N1 stands for the first of several known types of the protein neuraminidase.

The reason it is typically called "H5N1", is because that is the most distinguishing difference between it and other kinds of influenza. For example, the Spanish Flu was "H1N1".

"H", for hemagglutinin, put simply, is the way the influenza binds to a cell to infect it. If it cannot bind to a cell, it cannot gain entry to it and will die. There are 16 different *known* kinds of "H", from "H1" to "H16". But up until recently, only "H1", "H2" and "H3" were known to be able to infect human cells.

This is what makes "H5N1" so dangerous, because it is a completely new technique for the influenza to attack human cells, for which there is no acquired immune defense. It is what makes it a "new" disease, and extra deadly.

The "N", for neuraminidase, again put simply, is the technique the replicated virus uses to bust out of a cell it has used to reproduce itself, so it can attack other cells and spread to other animals. There are 137 types of "N", but only type "N1" and "N2" have been identified with human epidemics, though "N3" and "N7" have been associated with some isolated deaths.

H5N1 is very novel in nature, as well. This is demonstrated by its unique ability to infect a large number of very different host species, including cats, which share no other influenzas with humans. It has even been found in some fish, though whether it injures them has not been determined.

On top of everything else, there are a very large number of strains of H5N1 and other flus. These sub-sub-sub types are because influenza has a great number of "flexible" or unstable genes in its RNA, making them very prone to both mutation and gene transference between both other viruses and host cells.

This is why each year there are different strains of the flu needing different vaccinations. The vaccines are actually blends that attempt to cover a wide range of different strains, based on the best guesses of the most dominant strains being spread in the public. But an influenza outbreak can and does mutate enroute, either to less or more virulent strains, which can make a vaccine more or less effective.

But acquired resistance is not the only protection or defense we have against influenza. A large percentage of the population of North America, and many in Europe, have a genetic inhibitor to viral cell adhesion, which has been traced to the bubonic plague of the 15th and 17th Centuries. It is not yet known if it affords protection to the "H5" factor.

Some ionic metals may help protect against the flu by inhibiting viral reproduction in some way. This may give some people enough time for their immune system to adjust to the invader, by reducing the speed in which it attacks the body.

The immunological response to the Avian flu may turn out to be as deadly as the disease, because an overreaction of the immune system, known as the "Cytokine Storm" effect, can destroy the lungs. Unfortunately, immune system inhibitors tend to be extraordinarily toxic, as a rule, often associated with chemotherapy.
Posted by Anonymoose 2007-11-14 13:42||   2007-11-14 13:42|| Front Page Top

#2 Very good summary Moose, but I'd take issue with one statement,

This is demonstrated by its (H5N1's) unique ability to infect a large number of very different host species,

The species jumping is a characteristic of influenza viruses. It's surprising the ease with which all variants jump species, particularly between birds and mammals. I'd say influenza has evolved to do this and hence cause cross species epidemics.
Posted by phil_b 2007-11-14 15:52||   2007-11-14 15:52|| Front Page Top

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