• Avian influenza (bird flu), is an infectious disease in birds which is caused by type A strains of the flu virus.
• The current outbreak is caused by the H5N1 strain, which can be transmitted to humans, causing severe illness and often death.
• Initial symptoms of bird flu in humans may be similar to ordinary flu.
• Scientists are concerned that the bird flu virus could mutate and form a new, more contagious and dangerous strain.
• There are flu drugs to help prevent and treat the disease, but their availability is limited.

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What is bird flu?
Bird flu, or avian influenza, is an infectious disease of birds which is caused by type A strains of the influenza virus.

There are 15 different types of bird flu known to regularly infect birds around the world. Most strains of bird flu infect birds and can potentially infect other species such as pigs, but do not infect humans. The current outbreak, however, is caused by a strain known as H5N1, which is highly contagious and quickly fatal among birds, and it can be transmitted to humans, causing severe illness and often death.

The current outbreak of bird flu is different from earlier ones in that authorities have been unable to contain it. Bird flu activity is currently highest in Asia (centred on Vietnam) but has been found in other countries, including South Africa.

Bird flu and SARS
Bird flu is not the same as SARS (severe acute respiratory syndrome). The symptoms of these two diseases are similar, but they are caused by completely different viruses. Also, the SARS virus was (thus far) one isolated episode in human terms, whereas bird flu is an ongoing problem.

How is bird flu transmitted?
The H5N1 virus spreads easily from the faeces of wild birds to poultry on farms, and these domestic birds spread it to others. In addition, avian influenza viruses can be spread from farm to farm by contaminated equipment, clothing, vehicles and animal feed.

Humans generally acquire the virus through direct contact with infected birds or their faeces. People thus infected can occasionally transmit it to other humans, although the disease tends to be milder in those who catch it from an infected person.

The risk of mutation
Medical scientists are concerned that the bird flu virus could mutate and combine with a human influenza virus into a form that would be easily transmitted among humans. The longer this strain circulates around the world, the greater the chance that it will combine with a human influenza virus.

The resulting virus likely would be one to which humans have not been previously exposed, and therefore have not developed immunity against. With no immune defenses, the results could be catastrophic, as was the 1918-19 Spanish flu pandemic, which killed tens of millions of people.

Symptoms of bird flu
Although the exact incubation period for bird flu in humans has not yet been established, the illness seems to develop within one to five days of exposure.

Symptoms may initially be similar to those of ordinary flu, and include fever, cough, sore throat and muscle aches. Eye infections may occur. People with H5N1 may develop severe complications, particularly pneumonia and acute respiratory distress, the most common cause of death from the disease.

Treatment and prevention
There are flu drugs that may be used both to help prevent people from catching bird flu and to treat those infected. The newer flu drugs Tamiflu and Relenza appear to be effective weapons in fighting the disease – though it is feared that supplies could run out quickly in the event of a widespread human outbreak. Tamiflu is not available in South Africa.

There is no vaccine available against bird flu, but research is ongoing to develop one. The concern is that roll-out of such a vaccine will not be possible in time to prevent a widespread outbreak, should one occur.

Rapid elimination of the H5N1 virus among infected birds and other animals is a necessary and vital means to prevent a major outbreak. Authorities need to destroy infected or exposed flocks of chickens and other birds to help prevent further spread of the virus and reduce opportunities for human infection.

Reviewed by Dr Jane Yeats, Department of Virology, University of Cape Town
 

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