An outline of the nature of the avian influenza, including what the disease is, why it might or might not be the next pandemic, and current efforts to prevent it from becoming a worldwide threat.
What It Is
Avian influenza, or bird flu, is an extremely common strain of influenza which occurs naturally in bird populations. It is caused by Type A strains of the flu virus, and was identified by Italian scientists over 100 years ago.
It is thought that all birds are susceptible to the more than fifteen varieties of avian influenzas, with some species being particularly vulnerable. While migratory waterfowl often carry and suffer mildly from the disease, domestic poultry are the most susceptible to rapidly contagious, often fatal variations. All known outbreaks of the highly pathogenic influenza disease have originated from this A strain, specifically the H5 and H7 subtypes.
Usually these outbreaks are a result of domestic poultry populations– especially chickens and turkeys – coming into contact with migratory waterfowl like water ducks. Many outbreaks occur because the generally weak pathogen spread from the migratory birds mutates quickly into a more deadly form among the closely quartered domestic flocks.
For example, during an outbreak in 1983-1984 of birds in the United States, the H5N2 type influenza strain was initially a weak form of the flu with a low mortality rate, but within 6 months of the initial spread of the infection, the virus grew into a highly fatal disease with a bird mortality rate of almost 90%. This required the destruction of almost 17 million birds to prevent further occurrence.
When an outbreak occurs or is feared, it is standard to quarantine diseased populations of birds. However, the virus is both highly contagious and long-lived, so it can be transmitted easily from population to population via mechanical means (through contaminated machinery, manure, cages, vehicles or clothing.) Recent studies have shown that “a single gram of contaminated manure can contain enough virus to infect 1 million birds.” (Source: World Health Organization, "Avian influenza frequently asked questions") Thus, containment efforts are not always highly effective.
Bird influenza does not usually infect animals other than birds or pigs, but human infections were first reported in Hong Kong in 1997. Eighteen people became infected with the bird flu and developed severe respiratory distress which led to the deaths of six victims. Investigation into the cases revealed that close contact with live, infected birds, and the ability of the virus to mutate, allowed the influenza to jump directly to humans. Fortunately, though some secondary transmission of the disease occurred from worker to worker, the symptoms were not severe and the victims recovered. Alarmed by this transmission directly from birds to humans, Hong Kong immediately destroyed over 1.5 million birds, which many believe avoided a pandemic, or widespread outbreak.
Since the 1997 Hong Kong deaths, several other cases of bird influenza infections in humans have cropped up in the Netherlands, China, Thailand and Vietnam.