The dangerous swine flu virus has the ability to reach deep into lungs and intestines, according to studies on ferrets. This study might explain why the symptoms of swine flu are different from those of seasonal flu.

The studies were done by two separate groups that have been using ferrets to investigate how destructive H1N1 virus is, and how easily it is transmitted. One of the studies was guided by Terrence Tumpey at the Centers for Disease Control and Prevention in Atlanta, Georgia, whose colleagues put droplets of three different swine flu viruses, and one 'seasonal' flu virus into the noses of ferrets.

Some of the ferrets shared cages with uninfected ferrets and few were kept in cages next to other ferrets sharing only air. It was noticed that ferrets with the strains of swine flu lost more weight than ferrets with seasonal flu. The swine flu virus even reached lungs and intestines in some ferrets. This matches with examinations in humans that some patients suffered vomiting and diarrhoea.

The second study was guided by Ron Fouchier at the Erasmus University Medical Center, Rotterdam, the Netherlands, and it was noticed that the virus could indeed reach the lungs.

"This is the first indication of how pathogenic swine flu really is. In the field that conclusion is hard to draw," Nature magazine quoted Fouchier as saying.

Ferrets have long been used as a specimen for flu because they show symptoms that are seen even in humans and tend to last same time.

The studies have been published in Science.