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Avian Flu Virus Subtype H5N1

Of the 15 avian influenza virus subtypes, H5N1 is of particular concern for several reasons.  The foremost reason is that Avian Flu A Virus Subtype H5N1 has the ability to be transmitted and cause severe disease in humans.  There has been two documented cases of severe outbreaks leading to the deaths of humans.  In 1997 in Hong Kong, the H5N1 subtype led to the hospitalization of 18 people and the deaths of 6 of those people.  In early 2004, the H5N1 subtype caused severe poultry epidemics in Southeast Asia.  Although it was reported that the outbreak was controlled by March, a total of 23 people in Thailand and Hong Kong had died from the disease. 

Another reason why the H5N1 subtype is concerning is the fact that it is a “highly pathogenic” flu form in susceptible poultry species.  Since the virus is highly pathogenic, it increases the chance of other birds contracting the virus.  This makes the virus highly contagious, and is the reason why the slaughter of all birds within the vicinity of infected birds is required to minimize, or prevent, an outbreak. 

A study by the World Health Organization (WHO) in collaboration with St. Jude Children’s Research Hospital (Memphis, U.S.) was conducted on ducks to further understand the nature of this subtype.  Researchers found that the highly pathogenic H5N1 virus replicates in the respiratory and intestinal tracts of experimentally infected domestic ducks and contact ducks.  Large amounts of virus (103.5 – 105.5 particles per ml) are excreted via the respiratory route as well as in feces.  All infected ducks shed virus for 11 days and some for 17 days and longer, thus facilitating further spread at live poultry markets and by migratory birds.  The amounts of H5N1 virus shed are sufficient to allow transmission of H5N1 infection directly from apparently healthy ducks to chickens.

The WHO is particularly concerned about subtype H5N1 ability to mutate rapidly.  Thus the longer the virus subtype is around, the higher the probability it will mutate into another form that may be potentially more pathogenic to both birds and humans.  In addition, H5N1 has been reported to have a propensity to acquire genes from viruses infecting other animal species.  This too, may produce a “hybrid” form of the influenza virus.  If flu viruses infecting humans are thrown in the mix, then the new hybrid flu virus may be easily transmitted from humans to humans.  A new form of human flu virus can be devastating as history tells us.  One only needs to look back the Spanish influenza pandemic of 1918-1919, which killed an estimated 40-50 million people around the world.  It is widely believed that the Spanish Influenza virus evolved from bird-human flu interactions.  A research team had analyzed the structure of the gene and discovered how subtle alterations to the shape of a protein molecule had allowed it to move from birds to humans with such devastating effects.