With luck, the world will escape the latest outbreak of bird flu with no more than the 6 human victims already blamed on it and the loss of millions of chickens. But public health experts around the world worry for a much greater disaster: A catastrophe they say is among the worst imaginable, a global outbreak of an entirely new form of human flu.
There is no clear sign that will happen. Nevertheless, Avian Influenza's sudden sweep through Asia, along with its tendency for mutating, leave many wondering about the virus potential for rampant spread among humans. It is a possibility the medical journal The Lancet calls "massively frightening."
"The question everybody is asking is, 'Is this the progenitor to a pandemic?'" says Dr. Gregory Poland, chief of vaccine research at the Mayo Clinic.
Influenza pandemics typically strike 3 or 4 times in a century. The worst in the past 100 years was the 1918-19 Spanish flu epidemic that caused an estimated 40 million to 50 million deaths. Another epidemic is considered inevitable and perhaps overdue, but when it will happen and how bad it will be is almost totally unpredictable.
The nightmare this time would be a "Flu Virus" leaping from birds to people and spreading, introducing a disease for which humans have absolutely no natural defense.
The potential source is the virus strain of Bird Flu that has moved rapidly through parts of Asia since December, infecting chickens in Vietnam and Thailand and at least 4 other Asian countries.
Millions of birds have died of the flu or were destroyed by workers trying to contain the outbreak. The World Health Organization (WHO) says eliminating this "animal reservoir" of Bird Flu is very urgent.
Avian Flu is naturally carried by wild ducks, and the virus does normally not attack creatures other than birds, poultry or pigs, so experts are especially concerned that this bird flu is occasionally mutating and infecting humans.
Human cases have so far been reported in Vietnam and Thailand, including six deaths as of Saturday in Vietnam, the WHO said, and one suspected death in Thailand. Experts believe all caught the virus from chickens, not from other people.
"We know there are 2 possible ways a new pandemic strain can emerge," said Dr. Steve Ostroff, deputy director of the National Center for Infectious Diseases at the Centers for Disease Control and Prevention. One is a human flu virus that resurfaces after years of dormancy, so people have no defense built up from earlier attacks. The other is a non-human variety acquiring the ability to mutated and infect people and spread.
The latter may happen if somebody already infected with a human flu virus also catches the bird virus. Inside the body, these two may recombine into a new mutant, part-human virus, part-bird virus.
The more people that are around infected chickens and other poultry, experts say, the more chances there are for such a Influenza Pandemic disaster is to occur.
"If the virus continues to spread in chickens, it may adapt itself so it can grow in humans," says Dr. Arnold Monto, a University of Michigan epidemiologist. "If then the virus starts to transmit from human to human, then we are concerned this is the start of the great pandemic."
The first time an avian flu virus was found to have infected people was in Hong Kong in 1997. At least 18 people fell severely ill and 6 died. Experts believe a pandemic may have been averted that time by the rapid slaughter of Hong Kong's entire poultry supply, an estimated 1.5 million birds were killed in three days time.
That flu virus was the H5N1 variety, one of 15 known subtypes of Avian Flu. The WHO calls it worrisome for several reason: It mutates rapidly and tends to acquire genes from flu viruses in other animal species; it is clearly dangerous to humans; and it spreads very quickly. Infected birds give off the virus for at least 10 days in their feces and oral secretions.
H5N1 appeared again last February, when two members of a family returning to Hong Kong from China became ill. One died and the other recovered. How and where they got infected was never discovered.
The disease now circulating in Vietnam, Thailand and the rest of Asia is of the same H5N1 strain, but it is so widespread that a quick purging, like Hong Kong accomplished 7 years ago, is unlikely. Testing shows the virus has already mutated but has not yet picked up any genes from the known human flu viruses.
If a bird flu pandemic occurs, could it be stopped? Many experts fear not. Flu is so contagious that quarantining victims, a method that eventually contained the SARS epidemic last year, is unlikely to work with the Avian Flu.
Studies suggest that prescription drugs used to treat human flu strains could eventually keep people from catching Bird Flu. However, shortages in those drugs were reported during this winter's U.S. flu outbreak, and supplies would quickly run out during a pandemic. No country has enough stocks of the drugs, Tamiflu, Relenza and the older amantadine and rimantadine.
The WHO is already working on a prototype vaccine against the Bird Flu. But even the standard annual flu shot takes 6 months to manufacture, and experts doubt a new vaccine could be ready in time to fight a pandemic.
If there is evidence the bird flu is producing significant illness in humans, "there would be a full-bore effort to produce a vaccine," says the CDC's Ostroff. "It's hard to predict the timeliness of it and how widely it could be put into people's arms."
Editor's Note: Medical Editor Daniel Q. Haney is a special correspondent for The Associated Press.
