Avian Influenza

What causes avian influenza?

Avian influenza (also known as 'Bird Flu' and 'Asian Bird Flu') is a disease carried by birds, which affects some species worse than others. Avian influenza viruses are carried in the intestines of wild waterfowl, but mortality from the viruses is low among this group. However, when domestic poultry come in contact with the virus, the disease can be very contagious and mortality can be very high, with birds dying on the same day that symptoms appear.

Avian influenza is caused by various viruses that are related to human influenza viruses, however the H5N1 strain is the most virulent and the most likely to mutate if left to circulate in poultry populations. That is the reason that entire flocks are destroyed, when this strain is discovered in domesticated birds. The carcasses are disposed of carefully, and the area is quarantined and thoroughly disinfected.

How is avian influenza spread?

Avian influenza viruses are virulent and spread quickly. Since the virus is carried in the birds' intestines, the bird droppings are full of the virus and contaminate everything the droppings touch, first the soil, then clothes (especially shoes and boots), vehicles and equipment, and food and cages in the commercial environment. Where poultry is allowed to free-range, wild birds often share the water and feed, making it a simple matter for the infection to spread to the domesticated birds.

Vaccines have been developed that seem to control avian influenza viruses, but vaccinating poultry is only viable in large-scale commercial settings and the vaccine has to be updated as the viruses mutate. Vaccinating domesticated flocks in poorer countries is more problematic, as poultry is kept in the backyards, and is often let into the house at night during the winter.

It would be very difficult to cull these flocks in time to prevent an epidemic and culling is devastating for the families that depend on them for food and income. Under these circumstances it can take years before an outbreak of avian influenza is brought completely under control.

Is the avian influenza virus dangerous to humans?

Usually these viruses are not passed from birds to humans, unless the humans have had contact with the blood and/or droppings of an infected bird. From the time of contact with the avian influenza virus, to the onset of bird flu symptoms, is usually from 3-5 days, but can be as long as a week.

The big worry is that the avian influenza virus will mutate, and this new virus will be able to pass from human to human easily. Humans would have no immunity to the virus, which could be highly pathogenic and subsequently cause a bird flu pandemic. There have been several cases in Indonesia recently (May 2006) of what appears to be human to human to human transmission, which is causing concern around the world.