Why Swine Flu Differs From Seasonal Flu

July 3 -- THURSDAY, July 2 (HealthDay News) -- Scientists have uncovered some intriguing clues about why the new swine flu frequently brings on gastrointestinal distress and vomiting, symptoms not usually associated with seasonal flu.

In experiments with ferrets, research teams in the United States and the Netherlands found that the new H1N1 flu virus replicated more extensively in the respiratory tract, going to the lungs, whereas the seasonal flu virus stayed in the animals' nasal cavity. The U.S. team also found that the new virus, unlike the seasonal one, went into the ferrets' intestinal tract.

Such distinctions, the U.S. researchers said, can make a difference in establishing appropriate public health responses as the pandemic continues around the world, so far sickening more than a million people in the United States alone.

"Findings from the study demonstrate that, in ferrets, the novel 2009 H1N1 influenza virus leads to increased morbidity and increased respiratory disease when compared to contemporary seasonal human influenza viruses," said researcher Terrence M. Tumpey, a senior microbiologist in the influenza branch of the U.S. Centers for Disease Control and Prevention in Atlanta.

"Additionally, virus transmission was less effective in ferrets infected intranasally with novel 2009 H1N1 influenza virus, compared to those infected with contemporary seasonal human influenza viruses," he added.

The reports are published in the July 2 online edition of Science.

When both teams looked at how easily the new H1N1 virus can be transmitted, they came to different conclusions, however.

The Dutch researchers found that the new H1N1 virus and the seasonal flu virus were equally good in infecting the animals.

But Tumpey's team found that the swine flu virus might not be transmitted as easily as the seasonal flu virus. "The novel 2009 H1N1 influenza viruses exhibited less efficient respiratory droplet transmission in ferrets, in comparison to the high-transmissibility of a seasonal H1N1 virus," he said.