WASHINGTON—Authorities cite a long list of reasons to fear a possible bird-flu pandemic, but they also say there are reasons not to panic—at least not yet.
The concern is that the H5N1 strain of bird—or avian—flu virus that's sweeping across bird flocks in Asia and Eastern Europe might learn to jump between humans, like the 1918 "Spanish flu" that killed as many as 50 million people worldwide.
"That's why every virologist in the world is flying around with his hair on fire," said Dr. Tara O'Toole, a virus specialist and director of the Center for Biosecurity at the University of Pittsburgh Medical Center.
"A lot can be done to lessen the calamity of pandemic flu if you do it beforehand," O'Toole said. "Once you're there, you're cooked."
Here are some of the factors that worry the experts:
_Humans have no immunity to the H5N1 virus. It's a relatively new strain that's beginning to break out of its Southeast Asia homeland. The last pandemic was 37 years ago, and experts consider another one overdue.
_This virus is extremely virulent. It kills 100 percent of the animals it infects, and, so far, 50 percent of the humans who catch it. The common, seasonal flu isn't nearly so lethal. Even in the 1918 pandemic, the death rate was less than 5 percent. Noted flu-vaccine researcher Robert Webster has called H5N1 the "hottest" virus he's ever worked with.
_Unlike seasonal flu, H5N1 attacks more than just the respiratory system, killing by pneumonia or secondary bacterial infections. This strain also causes gastrointestinal disease, meningitis and devastating infections.
_The recent reconstruction of the Spanish flu virus shows that a few small mutations are enough to make bird flu able to move from human to human, the most important barrier to a new pandemic.
_There's no vaccine for the H5N1 virus. Three are undergoing preliminary testing, but they're designed to work against the type of virus that originates in birds, not in humans. If a person-to-person virus develops, it'll take months to make a vaccine for that strain.
_Even if there were an approved vaccine, the production system is grossly inadequate. Nine companies in the world are making vaccines for seasonal flu, but they have little capacity to switch to H5N1 vaccines. "They have no market for these vaccines right now," said Dr. Arnold Monto, an epidemiologist at the University of Michigan, Ann Arbor.
_Antiviral drugs—which minimize the effects of a virus and may provide some protection against infection—are in short supply and of uncertain effectiveness. The most popular medicine, Tamiflu, would have to be taken for at least eight days at very high doses to work. It hasn't yet been proved effective against H5N1. Flu viruses have developed resistance against another common drug, amantadine, rendering it virtually useless.
_The flu virus is contagious for at least a week before symptoms appear and after the patient recovers. This makes it almost impossible to contain. "There's no stopping it," O'Toole said.
_Public health systems worldwide are unprepared for a mass epidemic. Only a few U.S. states and cities have made plans. Federal preparation is "zero," said James Lee Witt, the Federal Emergency Management Agency director in the Clinton administration. Southeast Asian countries where H5N1 is exploding lack adequate scientific and medical facilities.
_International travel can speed the transfer of the virus around the world in days, much faster than in previous pandemics.
_Crowding and poor sanitation in mega-cities, especially in underdeveloped countries, makes it difficult to contain infection. In some lands, poultry and other animals live in intimate contact with humans, allowing the virus to spread to people. "I worry about the developing world," Monto said.
_Hospitals, doctors and nurses would be overwhelmed, perhaps incapacitated, in a pandemic.
_Essential services, such as police, transportation and power, could be knocked out by a lack of healthy workers.
_ A military quarantine, suggested by President Bush, would be unenforceable.
On the other hand, experts offer reasons not to overreact to the threat:
_The danger is still hypothetical. It may peter out after doing relatively little harm, as happened with hanta flu, swine flu and the SARS viruses. "Anybody who says we're on the verge of a huge pandemic is speculating," said Dr. Marc Siegel, an internist at the New York University School of Medicine and author of a new book, "False Alarm: The Truth About the Epidemic of Fear."
_The H5N1 virus hasn't yet mutated to a form that can be easily transmitted from person to person. This is a high hurdle that it may never leap. "The big unknown is when a flu virus will be selected that can transmit from person to person," said Dr. Martin Blaser, the chairman of the department of medicine at NYU Medical Center and the president of the Infectious Diseases Society of America. "Hopefully, we will be adequately prepared when that occurs."
_The only confirmed deaths due to direct human transmission were among close relatives: a child, her mother and her aunt in Thailand. "The Thai case is an anomaly. It doesn't mean very much," said Gregory Evans, the director of the Center of the Study of Bioterrorism and Emerging Infections at the Saint Louis University School of Public Health.
_Even if person-to-person transmission occurs, a vaccine for that strain could be developed in a few weeks and production could begin in a few months. Thus, protection would be available next year.
_People have been receiving flu shots for decades. That should provide some partial immunity, Siegel said.
_The flu virus tends to become milder after it's widespread in humans. That could reduce the fatality rate.
_Authorities around the world have recognized the threat and are acting to reduce it. "We're beginning to deal with the danger more realistically," Monto said.
_Dozens of countries are stockpiling antiviral drugs that could reduce the impact of bird flu. Bush has made vaccine development a national priority. A comprehensive action plan is promised shortly. Congress OK'd nearly $4 billion to produce antivirals. Officials in affected countries, such as Vietnam, Turkey and Romania, are destroying infected flocks and isolating exposed communities.
_Modern medicine has tools to defend against bird flu that were unavailable in 1918. Surveillance and sanitation have advanced significantly.
_People can do things themselves to reduce the chance of infection. "They can stay at home and avoid coming in contact with other people," Evans said. "If they need to go out, they can wear a mask."
_The military could be used, not to blockade highways and bridges, but to deliver food and medicine to people in their homes, seeing who's sick and who isn't.
"Can disaster be avoided? The answer is a qualified yes," Michael Osterholm, the director of the Center for Infectious Disease Research and Policy at the University of Minnesota, wrote in the summer edition of Foreign Affairs. "Although a coming pandemic cannot be avoided, its impact can be considerably lessened."
(c) 2005, Knight Ridder/Tribune Information Services.
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