In 1918-19, the "Spanish flu" killed more than 50 million people worldwide, including at least 500,000 in the United States.

Now, scientists say they have found that the avian flu that´s emerging in the Far East shares some of the same genetic characteristics as the flu virus that caused the 1918 pandemic.

In findings published in the Oct. 6 issue of Nature and Oct. 7 issue of Nature, a team of researchers finished sequencing the genetic makeup of the 1918 flu virus.

They report that the H5N1 bird flu strain emerging in Southeast Asia has several of the same mutations as the deadly 1918 strain. This suggests that it might not need to combine with a flu strain already adapted to humans to cause serious infection.

Despite these ominous findings, the hope is that understanding what made the Spanish flu so deadly will lead to new vaccine targets and antiviral drugs that might protect and treat people should the avian flu become a pandemic.

So far, the avian flu has been transmitted from animals to people, but as yet it has not been transmitted from person to person. However, many scientists believe it is only a matter of time before person-to-person transmission occurs.

Starting in 1995, scientists began piecing together the complete protein-coding sequence of the 1918 virus. Samples of the virus were obtained from the lungs of victims, including one in Alaska buried in the permafrost.

"Using these materials, we have been able to piece together the entire genetic coding of the 1918 virus," said study co-author Dr. Jeffery Taubenberger, chief of the department of molecular pathology at the U.S. Armed Forces Institute of Pathology.

The sequencing of the 1918 virus was undertaken with two goals in mind, Taubenberger said: "First, to understand how this particular pandemic formed -- how did it get into humans, and how did the pandemic start? Second; to understand why this particular virus was so virulent."

The aim of the research, according to Taubenberger, was to discover "what can we learn from the lessons of 1918 that would help us prepare for a future influenza pandemic."

Some of the same genes found in the 1918 virus may also help make the avian flu particularly virulent, said study co-author Adolfo Garcia-Sastre, a professor of microbiology at Mount Sinai School of Medicine in New York City.

"This suggests that there are common themes responsible for the virulence of influenza viruses," Garcia-Sastre said. "In the case of these genes, we have a new target for the development of new antiviral drugs aimed at decreasing the virulence of highly pathogenic influenza viruses."

Dr. Julie L. Gerberding, director of the U.S. Centers for Disease Control and Prevention, is concerned about a looming influenza pandemic.

"We are very focused on the potential for a pandemic outbreak of influenza," Gerberding said. "Most experts agree it´s not a question of if, it´s a question of when. The current H5 outbreak in Asia, we are taking it very seriously."

Gerberding said there are many unanswered questions about avian flu. "Will this virus change and spread more efficiently in people? Why is this virus so lethal in chickens and people? How can we detect it, treat it? Can we prepare an effective vaccine?" Understanding the 1918 virus will help in preparing for the next flu pandemic, she added.

One expert agreed these findings are important.

"The complete sequence of the 1918 virus, demonstrating its avian origin, and focusing on those mutations that differentiate avian from human strains will be immensely helpful as we try to understand the factors that govern the epidemic behavior of the current crop of avian H5 viruses," said Dr. John Treanor, a professor of medicine, microbiology and immunology at the University of Rochester who is part of a group of researchers conducting promising preliminary trials of an avian flu vaccine.

"The pathway is now clear for determining the contributions of individual mutations in the 1918 flu towards its pathogenesis, information that will be directly relevant to assessing the threat posed by current H5 viruses," he added.

Another expert is concerned this latest information may not be used in time to prepare for an avian flu pandemic.

"The influenza pandemic of 1918 may well be the greatest scourge ever to afflict humanity, exacting a death toll greater than all the wars of the 20th Century combined," said Dr. David L. Katz, an associate professor of public health and director of the Prevention Research Center Yale University School of Medicine. "The virus that wreaked this havoc apparently developed in birds, and then jumped to people. In other words, it was avian flu."

The grave threat posed by avian flu is increasingly self-evident, Katz said. "As recognition of this danger spreads, more and more resources are being allocated to the study of influenza. But whether we磛e embraced this opportunity in time is neither certain nor under our control. An avian flu pandemic could begin at almost any time, and we are racing the clock."

More information

The U.S. Centers for Disease Control and Prevention can tell you more about avian flu.

SOURCES: Jeffery Taubenberger, M.D., chief, department of molecular pathology, U.S. Armed forces Institute of Pathology, Rockville, Md.; Julie L. Gerberding, M.D., M.P.H., director, U.S. Centers for Disease Control and Prevention, Atlanta; Adolfo Garcia-Sastre, Ph.D., professor, microbiology, Mount Sinai School of Medicine in New York City; John Treanor, M.D., professor, medicine, microbiology and immunology, University of Rochester, New York; David L. Katz, M.D., M.P.H., associate professor, public health, director, Prevention Research Center Yale University School of Medicine, New Haven, Conn.; Oct. 7, 2005, Science; Oct. 6, 2005, Nature