Avian Influenza - Bird Flu FAQ (I)

By Sachin A


As more and more cases of bird flu are reported, the world faces an immediate threat of a deadly pandemic. Pandemics (Global Disease Outbreaks) are known to be like flash floods. They start abruptly, spread fast and cause a lot of damage all over the world.

A few facts that everyone should know:

What is Avian Influenza?

As the name suggests, avian influenza refers to the infection caused by avian (bird) influenza (flu) viruses. These viruses are commonly found in intestines of wild birds and these birds can carry the viruses without getting sick. However the viruses can be pathogenic to domesticated birds like chickens, ducks and turkeys. Domesticated birds become infected through exposure to other birds or through surfaces contaminated by secretions and faeces of the infected birds.

These viruses are classified as Low Pathogenicity and High Pathogenicity. Most strains of Avian Influenza come under Low Pathogenicity Avian Influenza (LPAI) Group and produce mild symptoms in the infected birds. Common symptoms are ruffled feathers, decreased food appetite, decreased egg production, sneezing and coughing. Many times LPAI may go undetected.

High Pathogenicity Avian Influenza (HPAI) has more severe symptoms which include sudden death, loss of energy and appetite, decreased egg production, respiratory problems, facial oedema (swelling), poorly formed eggs and diarrhoea. HPAI can reach a mortality rate of nearly 100%.

What Is H5N1 strain of Bird Flu?

All flu viruses are classified as type A, B or C depending on their structural arrangement. Type A is responsible for lethal pandemics and is found in both animals and humans. Type B causes local outbreaks of flu. Type C is the most stable of the three and infected people show only mild symptoms of flu. Type B and C are usually found only in humans. Type B and C are more stable than type A and are not classified according to their subtypes.

Influenza viruses of type A are divided into subtypes and the naming is done on the basis of two proteins (antigens) found on their surface - Hemagglutinin (HA) and Neuraminidase (NA). Sixteen types of HA and nine types of NA exist. Thus a total 144 combinations are possible.

Thus H5N1 is a type A virus and gets its name from HA 5 protein and NA 1 protein present on its surface.

How Do Type A Viruses Cause A Pandemic?

Type A viruses are further classified into strains. These strains can continuously evolve into different strains. Their ability to exchange genetic material with other viruses and create new influenza viruses makes them unpredictable and difficult to fight with. Humans have to develop new immunity (antibodies) every time new strains are created.

Viruses cannot repair genetic damage, small changes known as "Antigen Drift", are continuously creating new strains of viruses. However when genetic material from Type A viruses from different species - say a bird and a human, comes together and merges, an entirely new strain is created. This is known as "Antigen Shift" Humans have no immunity to such a strain and the strain can spread rapidly causing a Pandemic.

How Is The Virus Transmitted To Humans From Birds?

Usually Avian Influenza viruses do not infect humans. Migratory birds act as carriers of these viruses and do not get affected by them. These birds then come in contact with domesticated birds such as chickens and turkeys and spread the infection to them. Domesticated birds may get the virus from contact with contaminated surfaces too. Once a virus infects domesticated birds, it can cause severe epidemic among the birds. Humans come in contact with infected birds or contaminated surfaces and pick up the virus.

In the human body, this avian flu virus then undergoes an antigenic shift, combines with genetic material of a human strain of influenza virus and creates an entirely new strain of virus against which humans have little or no immunity. These genetic reassortments may also take place is the body of a third species (susceptible to both avian and human viruses) like the pig, where an avian influenza A virus and human influenza virus mix their genetic information and produce a new virus which might be able to infect humans.

Why is H5N1 dangerous?

The first reported cases of H5N1 infections were detected in geese in 1997 in Southern China. A total of 18 human infections were reported and six of them succumbed to it. The infection spread quickly to poultry in Hong Kong. At that time a million and half chickens were culled in Hong Kong to keep the virus under control. The virus disappeared for a few years, but resurfaced in 2002 in Hong Kong again. Since then it has killed millions of birds in Asia and many cases of human infections have been reported.

The persistence of this H5N1 strain of virus is a great concern for humans. Although the virus does not spread from birds to humans easily, the severity of the infection of H5N1 in humans is frightening. The virus has killed every second person infected by it. These cases were reported in perfectly healthy individuals who had no past history of infections. However the greater concern for the world is the POSSIBILITY THAT THE VIRUS MAY MUTATE (UNDERGO ANTIGENIC SHIFT) AND CREATE A FORM THAT MAY SPREAD FROM HUMAN TO HUMAN. Such a strain of virus may result in a pandemic, killing millions of people worldwide.

Sachin A. is a Freelance Writer and specializes in articles that require extensive research. Check out this work at http://www.rightarticle.com