Swine Flu vs. Bird Flu: Which Is the Greater Pandemic Threat?


As health officials around the globe continue to monitor the swine flu outbreaks that have occurred within the past month, comparisons with the periodic bird flu outbreaks over the past decade are difficult to avoid.

Specifically, some may find themselves asking the question: Since the bird flu failed to spark a full-blown pandemic, should we really worry about swine flu?

Infectious disease experts say there are numerous key differences between the two viruses and their pandemic potential, and a new study published on Friday in the journal PLoS Pathogens hints at just one of these differences. In the study, British and U.S. researchers revealed that the bird flu virus becomes impaired at 89.6 degrees Fahrenheit -- the temperature of the human nose -- therefore making it less likely that it can spread from person to person.

The human nose, in other words, may simply offer too cold a climate to encourage the spread of the avian flu virus. Whether this will always be the case is not yet known, but the researchers said that a substantial mutation would have to occur in the bird flu virus before it would become a pandemic threat for humans.

"Bird viruses are out there all the time, but they can only cause pandemics when they undergo certain changes," said Wendy Barclay of the Imperial College in London, one of the study's authors. "Our study gives vital clues about what kinds of changes would be needed in order for them to mutate and infect humans, potentially helping us to identify which viruses could lead to a pandemic."

The study may also provide scientists with the mechanisms of virus mutation in general, allowing them to predict which viruses are more likely to spread to humans.

Dr. William Schaffner, chair of the Department of Preventive Medicine at the Vanderbilt University School of Medicine in Nashville, Tenn., called the study "very nice work that adds another explanation why the bird flu is not being transmitted readily in people."

Swine Flu Beats Bird Flu in Human-to-Human Transmission

"Previously it has been shown that the avian influenza viruses did not attach to the cells of the upper respiratory tract, but could attach lower down," Schaffner said. "The current study provides an additional potential explanation."

Ed Hsu, associate professor of public health informatics at the University of Texas School of Health Information Sciences and School of Public Health, agreed. "This study renders potential explanations for why Avian Flu virus does not effectively transmit from human to human -- an important indicator for raising pandemic level."

But Dr. Pascal Imperato, dean of the Graduate Program in Public Health at SUNY Downstate Medical Center in Brooklyn, N.Y., warned that the fact that this was an in vitro study -- in other words, one that took place in a Petri dish -- meant that more research would be needed to determine whether the findings are an accurate reflection of what happens in humans.

"The findings would need to be corroborated in order to have credibility," Imperato said. "That said, there are many other variables that determine the infectivity of a pathogen. While these findings are of interest, they really do not alter our current understanding of the pathogenicity of influenza viruses."

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