What is an avian influenza A (H5N1) virus?

Influenza A (H5N1) virus, also called H5N1 virus, is an influenza A virus subtype that occurs mainly in birds. It was first isolated from birds in South Africa in 1961. Like all bird flu viruses, the H5N1 virus circulates among birds worldwide, is very contagious among birds, and can be deadly.

Do bird flu viruses infect humans?

Past experience has shown that subtypes of the influenza A virus can sometimes cross over and cause illness in other species, such as humans.

The US-based Centres for Disease Control and Prevention says that while bird flu viruses do not usually infect humans, several cases of human infection have occurred since 1997, when the first human cases of H5N1 emerged in Hong Kong.

According to the World Health Organisation (WHO), of the few avian influenza viruses that have crossed the species barrier to infect humans, H5N1 has caused the largest number of cases of severe disease and death in humans. In the present outbreak, more than half of those infected have died - an unusually high mortality rate for a flu virus.

Most cases have occurred in previously healthy children and young adults.



How does bird flu spread?

Infected birds shed flu virus in their saliva, nasal secretions, and faeces. Susceptible birds become infected when they have contact with contaminated excretions or surfaces that are contaminated with excretions.

To date, most cases of bird flu infection in humans have resulted from contact with infected poultry or contaminated surfaces.

However, health officials worry that if the virus infects someone already carrying the more common human flu virus, the H5N1 virus may mutate into a more deadly form, easily transmissable between humans, creating the basis for a global pandemic.

How is bird flu treated in humans?

Studies suggest that the prescription medicines approved for human flu viruses would work in preventing bird flu infection in humans. However, flu viruses can become resistant to these drugs, so these medications may not always work.

Is there a vaccine to protect humans from H5N1 virus?

There currently is no vaccine to protect humans against the H5N1 virus that is being seen in Asia. However, vaccine development efforts are under way.

What drugs are available for treatment?

Two drugs are available. Tamiflu (generic name: oseltamivir), made by Swiss drug giant Roche, and Relenza (generic name: zanamivir), from GlaxoSmithKline, can reduce the severity and duration of illness caused by seasonal influenza.

However, health officials say neither drug should be taken without first seeking medical advice. Over use of the drug may build up viral resistance, they warn, making even these drugs ineffective.

Can a pandemic be prevented?

No one knows with certainty. The best way to prevent a pandemic would be to eliminate the virus from birds, but it has become increasingly doubtful if this can be achieved within the near future.

Is the world prepared for a pandemic?

Some countries are more prepared than others. In general though health experts say that despite an advance warning that has lasted almost two years, the world is ill-prepared to defend itself during a pandemic. The WHO has urged all countries to develop preparedness plans, but only about 40 have done so.