Bird flu is neither recent nor uncommon in wild bird species. Just like the flu caused by human pathogenic (disease causing) influenza viruses, it has probably been around for thousands of years, and mutates into various viral strains. It has become newsworthy since 1997, and thus brought to the attention of the general public, for three reasons:

1/. A relatively new and virulent strain of avian influenza virus H5N1 is zoonotic, meaning it can be passed through contact from birds to people and can result in the infected person's death; the World Health Organization reports 254 deaths as of February 5, 2009.

2/. The risk that this strain of H5N1 virus may further mutate within a human host into a strain that can be passed from human to human while retaining its lethality. The 254 deaths occurred in a total of 405 infected people, a 63% mortality rate; although many of these cases occurred in rural areas of less developed countries, where supportive medical treatment may have been minimal.

3/. There is an increasing incidence of infection by this strain in domestic bird flocks necessitating the slaughter and disposal of large numbers of birds at considerable economic cost.

The occurrence of bird flu in humans is most prominent in those who handle domestic birds for obvious reasons. Very few people physically interact with wild birds of any species. Even those who shoot wild bird species such as ducks for food or recreation, are unlikely to be infected because they are handling carcasses rather than live birds. Influenza viruses are predominantly spread via air-borne exudates produced by sneezing, coughing, etc; rarely produced by deceased animals. This is because influenza causing viral infections predominantly occur in the respiratory tract. As this is closely connected to the gastro-intestinal tract at the back of the mouth, top of the throat, virions (individual viruses) are also commonly excreted in the birds' waste. Something that bird hunters should take particular note of. All those handling bird carcasses should clean their hands thoroughly afterward, a protective mask over the nose and mouth would be advisable for those handling live birds.

Bird flu is thought to be primarily spread from wild birds to domestic flocks through the excrement of wild birds falling on establishments where domestic bird flocks are being raised. It can also be from intermingling at or on farm ponds. Long distance spread is generally accredited to migratory bird species, although there is some disagreement on this.

The arguments against are based on the immunosuppresive effect of the strain long distance, migratory flights put the bird under. With their immune systems degraded, infected birds should succumb to the disease and die en route.

The arguments for are based on circumstantial evidence supported by forensic genetics. Comparison of viral genetic data obtained from deceased birds links outbreaks that have occurred remote from each other, but are on the migration path of wild birds also found to have H5N1 with closely related genetic markers.

The current consensus is that the wide-scale spread is primarily through migratory birds. Local spread may pass either way, from wild birds to domestic or vice versa. People can still only get it from close contact with infected birds, and hopefully it will remain so.

Learn more about this author, Perry McCarney.
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