Scientists say new research has shown that the new H1N1 influenza strain (swine flu) is somewhat less contagious than seasonal flu, but appears to be more able to cause stomach upsets.
According to a team of researchers at the U.S. Centers for Disease Control and Prevention (CDC), they have found by means of genetic analysis and experiments in the laboratory, that the virus lacks a piece of genetic material that makes ordinary flu viruses so transmissible.
Scientists in the Netherlands have also found that the new H1N1 flu strain lives very well in the nose and they suggest it has the ability to stay around for a long time and could get worse.
The team at Erasmus Medical Center in Rotterdam found the virus lived well in ferrets and spread very easily from one to another - the ferrets apparently shed more of the new flu virus than seasonal flu from their noses.
The team also found that ferrets infected with the new swine flu virus became slightly sicker and took slightly longer to recover than ferrets infected with seasonal flu and they say this suggests that the new H1N1 influenza virus has the ability to persist in the human population, potentially with more severe clinical consequences.
In June the World Health Organization (WHO) declared the world was experiencing a pandemic of the new swine flu - the WHO's latest update says to date globally there have been 89,921 confirmed cases of swine flu including 382 deaths and health officials suspect there are likely to be a million or more cases in the United States alone.
The flu season usually ends in April in the Northern Hemisphere, but the new virus continues to cause widespread illness and is now circulating along with seasonal flu viruses during the Southern Hemisphere's winter.
Scientists at the CDC tested samples of the new virus taken from a California child who recovered from a mild bout of the new flu, a Texas child who died and a Mexican woman who had severe disease and compared it to ordinary, seasonal H1N1 flu, also by testing it in ferrets - ferrets develop flu in similar ways to humans.
The CDC team found that the ferrets did not catch the new swine flu from one another as easily as they catch ordinary viruses and unlike ordinary seasonal flu, where all the ferrets would become infected, with the new H1N1, only six out of nine animals became infected.
Experts say with seasonal flu 20 to 30% of household members are usually infected by a single flu patient but H1N1 swine flu appears to have a lower transmission rate.
They also say that all previous pandemic flu strains have had a specific genetic sequence in a gene called PB2 and the new H1N1 does not have this particular mutation.
Experts at the CDC say that H1N1 swine flu needs to be closely watched as any change may signal the virus is gaining the ability to spread more quickly and easily than it already does and may also mutate to become resistant to antiviral drugs; so far there have been two instances of this happening - one in Japan and one in Denmark.
The CDC team have also found that mutations allow the new H1N1 virus to live in the small intestine, which is something seasonal influenza cannot do, which may explain why so many swine flu patients have stomach upsets such as nausea and diarrhea.
Both teams of researchers confirm what doctors around the world are saying , that the new pandemic A(H1N1) influenza strain is slightly more pathogenic than seasonal influenza but nowhere near as dangerous as the 1918 pandemic virus or H5N1 avian influenza.
They disagree, however, on how easily the virus spreads with the Dutch team concluding that it does so very well, while the U.S. team believes that it's only moderately adept at jumping from one animal to the next or between humans.
Both studies are published in the journal Science.