Avian Influenza

by Dr. Andreas Lambrianides
General Surgeon, Brisbane Australia

Avian Influenza or 'bird flu', is an infectious viral disease that normally affects only birds. Since 2003,outbreaks of the H5N1 strain of avian influenza in poultry have occurred in countries including Vietnam ,Thailand ,Cambodia, Indonesia, China, South Korea, Kazakhstan, Malaysia, Mongolia, Japan and Russia. Over 100 confirmed cases of infection in humans have been reported, with around 60 deaths.

At present H5N1 subtype of influenza A dominates the thoughts of the medical and wider public both local and global. Lost amongst the deluge of information is the reason why communities are rightly concerned about this threat.

In dissecting out the reason we need to consider the past history of pandemic influenza and the rise of H5N1 influenza since 1997.

Our thinking about influenza has always been dominated by the great pandemics of 1957, 1968 , 1977, and most importantly of all, the 1918 pandemic. Much has been learned about the virus and the disease from the later pandemics but the key facts about the 1918 pandemic have been illusory until the past few weeks.

The 1918 pandemic was, the most devastating infectious disease in recorded human history. It stands apart from the subsequent pandemics in many ways the scale, the epidemiology, the severity so much so that it has always been felt that there was something different about the influenza subtype (H1Na) responsible. The problem was that it could never been identified in those times. The only possible remaining sources of the virus were in the tissues of victims and the pathology archives.

New molecular technology has allowed a reconstruction of the 1918 influenza virus front these sources.

The 1918 influenza virus, was different from the other pandemic subtypes ,and this was the result of mixing and exchanging genetic material between avian strains and animal strains of influenza. The 1918 influenza subtype appears not to have intermixed but to be an avian subtype that directly infected humans. Of even more concern is that there are close similarities between the 1918 subtype and H5N1.

The key points are:

1) H5N1 has spread widely through the migratory wildfowl population and this in turn has spread the virus geographically far and wide.
    The virus does not harm the infected birds.
2) H5N1 has from time to time infected the domestic fowl population with devastating consequences for the flocks. It would appear that
     the infection strain(s) of H5N1 are becoming more pathogenic as a number of bird species that are usually not susceptible have died.
3) H5N1 infection of humans is associated with a high mortality
4) A global population that as no immunity to this subtype nor do we have a vaccine at present. Antiviral drugs are available but supplies
     will have to be controlled.
5) A epidemiological record indicating that we are long overdue for an influenza epidemic.
6) A highly mobile human population.
7) Sporadic outbreaks occurring in communities that have inadequate resources to address the problem.
8) The impact that the S.A.R.S epidemic have on the community.

We now have a situation where two of the three requisites for building the trigger for an influenza pandemic, namely the lack of immunity and an influenza virus capable of infecting humans exist.

The last requirement:

It is the ability to be transmitted readily from person to person that is missing from the picture.

For this to occur either a mutation in the avian H5N1 in the wild or the development of a genetic hybrid, as a result of co-infection in a human or animal with the avian H5N1 and on of the other human or animal influenza viruses, needs to occur.

There is no confirmed evidence of person to person spread in the current H5N1 avian influenza outbreak. The latest evidence about the nature of the subtype that caused the 1918 pandemic is a concern. It points to a mutational event in a similar avian subtype that allowed direct infection of humans as well as human-to-human transmission.

People traveling overseas to avian influenza affected countries are currently only at risk of contracting bird flu if they have close contact with infected birds or raw poultry products. The virus is found in bird faeces and respiratory secretions and does not easily spread from birds to humans. The risk of contracting the disease from occasional contact with an infected bird, such as when traveling on public transport, is extremely low. Countries that import live chickens, raw chicken products or eggs, are at risk of contracting bird flu from handling, eating poultry, or poultry products.

The usual symptoms of avian influenza are similar to those of other forms of influenza, such as, high fever, cough, fatigue and aching muscles. Runny nose and sneezing are occasionally present. Antiviral medications such as oseltamivir (Tamiflu) and zanamivir (Relenza) can be used in the treatment of avian influenza. Antibiotics may be required for secondary bacterial infections such as pneumonia. Pneumonia is a very common complication of avian influenza. Around half of the confirmed cases of avian influenza have died, mainly from lung or other organ failure. Travelers to countries where avian influenza is present should: avoid situations where they may come into close contact with birds, such as poultry farms and live bird markets avoid raw chicken, eggs, and other poultry products. If it is necessary to handle or cook poultry and eggs, ensure that they are handled hygienically with careful attention to hand washing after handling, and that they are thoroughly cooked, as this destroys the virus. Wash hands regularly and more frequently than usual.