Nov. 29, 2004
MSNBC
HONG KONG - The bird flu virus is far more lethal than the SARS virus that struck Asia last year and could unleash a pandemic that could kill as many as 50 million people, a World Health Organization official said Monday.
A WHO estimate last week that H5N1 could infect up to 30 percent of the world’s population and kill between two and seven million people was a conservative estimate, said Shigeru Omi, regional director of WHO’s Western Pacific Regional Office.
“The maximum range is more ... maybe 20 to 50 million people,” Omi said in a speech in Hong Kong.
“It will be incomparable to SARS,” he said, referring to the Severe Acute Respiratory Syndrome epidemic that killed 800 people around the world in 2003.
While SARS had a mortality rate of around 15 percent, the deadly H5N1 strain of bird flu kills up to a third of the people it infects. H5N1 has proven to be versatile and is now able to latch itself onto more hosts, Omi said.
The virus is currently unable to leap from human to human, and as a result, cannot spread quickly through the population. However, scientists are worried that it may only be a matter of time before the virus mutates into a form that can spread between people.
“It has gone through huge genetic changes and become more pathogenic. It has affected not only birds, but cats, pigs and tigers ... ducks are now playing a more important role,” Omi said.
The virus has killed 32 people in Thailand and Vietnam this year and millions of chickens, ducks and other birds have been culled across Asia.
The rapid spread of bird flu, which is not uncommon among chickens and other fowl, has caught the attention of global health authorities. Click on the topics to learn more about the illness and why scientists are so concerned.
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.
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.
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.
The current outbreak of bird flu is different from earlier ones in that officials have been unable to contain its spread. An outbreak in 1997 in Hong Kong was the first time the virus had spread to people, but it was much more quickly contained. A total of 18 people were hospitalized with six reported deaths. About 1.5 million chickens were killed in an effort to remove the source of the virus.
Unlike the 1997 scare, this outbreak has spread more rapidly to other countries, increasing its exposure to people in varied locations and raising the likelihood that the strain will combine with a human influenza virus.
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.
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.
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.
POULTRY SLAUGHTER BAN
Almost all the human bird flu victims in Hong Kong, Thailand and Vietnam fell ill after direct contact with sick chickens.
With the illness now endemic in poultry farms, experts fear the virus may soon mutate into a form that can easily spread around the world. Pigs are seen as a likely next step.
Infected ducks now display no symptoms of the disease but shed huge amounts of the virus in their feces, a source of concern because ducks and chickens are often kept together in Asia and this could give rise to cross infection.
Two U.S. companies and a Japanese firm are working on a vaccine against H5N1 and clinical trials on its efficacy and safety have begun, Omi said. But he cautioned people against thinking that vaccines were a cure-all.
“Vaccines are very useful in reducing the scale of a pandemic but it is not a magic blitz in averting a pandemic,” Omi said.
Due to commercial reasons, mass production of vaccines would only start after a pandemic begins, which means it would only reach the public after a time-lag of at least five to six months.
NEW PROHIBITION
Hong Kong said Monday it may ban shopkeepers from slaughtering poultry in its battle against the virus.
Hong Kong scientists have been fighting to end the widespread practice of killing live chickens in markets since 1997, when the H5N1 virus first spread to humans and killed six people in the territory.
A food department spokeswoman said the government might set up a central abattoir or restrict slaughtering to a few areas.
Strong opposition from the poultry industry has prevented the government from stopping stall holders in markets from selling live chickens and ducks and slaughtering them in front of customers.
Hong Kong people like their food fresh and often shop in markets where they can pick the birds they want and have them killed on the spot. Many of the chickens are from mainland China.
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