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The rapid spread of bird flu, which is not uncommon among chickens and other fowl, has caught the attention of global health authorities. Here are the ABCs about this disease.

What is bird flu?

There are at least 15 different types of avian influenza that routinely infect birds around the world. The current outbreak is caused by a strain known as H5N1, which is highly contagious among birds and rapidly fatal. Unlike many other strains of avian influenza, it can be transmitted to humans, causing severe illness and death.

Bird flu is not the same as SARS (severe acute respiratory syndrome). Although their symptoms are similar, SARS is caused by completely different viruses. Influenza viruses also are more contagious and cannot be as readily contained as SARS by isolating people who have the infection.

Why the concern?

Influenza viruses are highly unstable and have the ability to mutate rapidly, potentially jumping from one animal species to another. Scientists fear the bird flu virus could evolve into a form that is easily spread between people, resulting in an extremely contagious and lethal disease. This could happen if someone already infected with the human flu virus catches the bird flu. The two viruses could recombine inside the victim's body, producing a hybrid that could readily spread from person to person.

The resulting virus likely would be something humans have never been exposed to before. With no immune defenses, the infection could cause devastating illness, such as occurred in the 1918-19 Spanish flu pandemic, which killed an estimated 40 million to 50 million worldwide.

How is bird flu virus transmitted?

In rural areas, the H5N1 virus is easily spread from farm to farm among domestic poultry through the feces of wild birds. The virus can survive for up to four days at 71 F (22 C) and more than 30 days at 32 F (0 C). If frozen, it can survive indefinitely.

So far in this outbreak, human cases have been blamed on direct contact with infected chickens and their droppings. People who catch the virus from birds can pass it on to other humans, although the disease is generally milder in those who caught it from an infected person rather than from birds.

If the virus mutates and combines with a human influenza virus, it could be spread through person-to-person transmission in the same way the ordinary human flu virus is spread.

What are the symptoms of bird flu?

Bird flu can cause a range of symptoms in humans. Some patients report fever, cough, sore throat and muscle aches. Others suffer from eye infections, pneumonia, acute respiratory distress and other severe and life-threatening complications.

How could bird flu be treated?

Flu drugs exist that may be used both to prevent people from catching bird flu and to treat those who have it. The virus appears to be resistant to two older generic flu drugs, amantadine and rimantadine. However, the newer flu drugs Tamiflu and Relenza are expected to work - though supplies could run out quickly if an outbreak occurs.

Currently there is no vaccine, although scientists are working to develop one. It probably will take several months to complete and may not be ready in time to stop a widespread human outbreak, if one occurs.

Culling an effective prevention measure

Rapid elimination of the H5N1 virus among infected birds and other animals is essential to preventing a major outbreak. The World Health Organization recommends that infected or exposed flocks of chickens and other birds be killed in order to help prevent further spread of the virus and reduce opportunities for human infection. However, the agency warns that safety measures must be taken to prevent exposure to the virus among workers involved in culling. (Sources: AP, CDC and WHO)

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