Public health officials are concerned that the avian flu, or "bird flu," could easily become a serious threat to human health worldwide. The following are some fast facts on this deadly disease.
Avian influenza is a contagious disease caused by a strain of the influenza virus.
Avian flu has two forms, a mild form and a fatal form that can cause death within 24 hours of the first appearance of symptoms.
The deadly form was first discovered in Italy in 1878.
All birds are believed to be susceptible to the virus, though some species seem to have more resistance than others.
Migratory waterfowl – ducks, geese, etc. – often carry the virus, but seem to have the most resistance to severe infection.
Domestic poultry (like chickens and turkeys) are especially vulnerable to avian flu outbreaks and are the least likely to recover from the disease.
Some researchers believe contact between waterfowl and poultry may be a frequent cause of epidemics. Live bird markets, where caged birds are kept in close quarters, have also been cited as a way of spreading avian flu epidemics.
The virus can spread directly from bird to bird, and from farm to farm through contaminated equipment (like cages), feed, clothing, vehicles and shoes. Rats, too, can carry the virus on their feet.
The virus can survive for three months in bird droppings; the virus can also survive in water for up to four days.
Health experts are alarmed at how quickly the avian flu virus can mutate to a form that is deadly and resistant to medication. It can also mutate to a form that passes easily from one species to another, or among animals of the same species.
A 1983-84 outbreak of avian flu in Pennsylvania began with low mortality, but within six months the virus mutated to a deadlier form, with 90 percent of infected birds dying.
The deadly strain of influenza virus currently found in Southeast Asia is known as the H5N1 strain. It can pass from birds to humans, but cannot yet pass from human to human.
Experts fear that if the H5N1 virus mutates to a form that does pass from human to human, it could set off an international pandemic.
The standard measures taken to control an outbreak of avian flu include quarantine of an infected flock, the destruction of entire flocks and the proper disposal of carcasses.
Unless prompt and consistently strict controls are implemented, epidemics can take years to contain – a 1992 epidemic in Mexico was not controlled until 1995.
The first known human cases of avian flu occurred in 1997 in Hong Kong, when the H5N1 virus infected 18 people, six of whom died.
A rapid response by Hong Kong authorities – some 1.5 million birds were destroyed in three days – averted what might have become a public health catastrophe.
Since then, deadly avian flu outbreaks among humans have occurred in the Netherlands, Indonesia, Thailand, Cambodia and Vietnam. At least 60 people worldwide have died of the H5N1 virus since 2003.
Other forms of the avian flu (not H5N1) have occurred in humans in Virginia and New York.
In humans, the avian flu is marked by fever, sore throat, cough, muscle aches, eye infections and, in fatal cases, severe respiratory distress and viral pneumonia.
There is no vaccine yet available for the H5N1 virus, but several companies in the U.S. and Europe are racing to develop one.