For more than a century, bird flu has circulated among birds, particularly domesticated fowl, but recent attention has been called to avian influenza since some strains infected humans. No longer is bird flu relegated to pigs and birds, as the virus has strengthened and mutated, resulting in a contagion that can move from bird to human. Human cases of bird flu have caused infections and death across the globe as scientists struggle to identify the dangerous strains and prevent a fatal pandemic.
We have long known that avian influenza existed in animals, often killing wild and domestic populations. These viruses belong to related kinds of influenza that evolve and mutate just like any virus. We used to be primarily concerned with losing valuable birds that were providing eggs or meat to poultry farmers. However, in 1997 that changed when bird flu appeared to prove fatal for people in Hong Kong.
A pathogenic, or active, strain of bird flu will kill birds quickly and spread rapidly through a population. If a wild, migratory bird catches the flu, it can carry it many miles to other wild or domesticated groups. These viruses evolve in two ways, through drift and shift. Drift refers to inexact replication, such that newer viruses are further from the original genetic material, but share enough DNA that they are still only spread amongst a single species. When a virus shifts, it means that the genes of one virus mix, or breed, with a different virus, usually inside a carrier. Due to shift, bird flu mixed with a human kind of flu, and was thus able to infect humans through direct contact with birds.
Human cases of bird flu are incredibly alarming, and raised the concern of virologists and government agencies in China, Hong Kong, Vietnam, Canada, and other countries. This imminent pandemic could only be controlled by the vast slaughter of millions of fowl to contain the virus that spreads by air, water, and soil. The bird flu is especially dangerous because our immune systems don't have any antibodies to handle something that used to be relegated to animals. Thus, it takes hold with unprecedented force, settles in the lungs, and resists anti-viral and anti-bacterial medication.
Most health experts researching and fighting the incidence of human bird flu do not have an optimistic outlook. They point out that the pathogen has not appeared to evolve such that human-to-human contact is contagious, yet it remains that people working with fowl, swimming in infected rivers, playing in an area where carcasses were buried, or breathing air near a poultry processing plant, can lead to infection.
Thus far, doctors have been able to diagnose bird flu, identify the specific strain, and target the proper disposal of infected birds. Yet they are ineffective at treating the resultant respiratory infection, leading to fatalities. They note that flu epidemics and pandemics appear to be inevitable given the history of contagious disease over the last few centuries.