By Tan Ee Lyn
HONG KONG, May 12 (Reuters) - A leading virologist has described the new H1N1 influenza virus as "very unstable", meaning it could mix and swap genetic material when exposed to other viruses.
The new virus, which has infected 5,251 people in 30 countries and killed 61, has displayed great efficiency in spreading among people, said Guan Yi, a microbiologist with the University of Hong Kong.
"This virus has been around only a few months, it is very unstable ... and we know that its presence is dramatically increasing in human population, so the chance of it meeting with H5N1 is actually increased," Guan said in an interview on Tuesday.
"Both H1N1 and H5N1 are unstable so the chances of them exchanging genetic material are higher, whereas a stable (seasonal flu) virus is less likely to take on genetic material."
While H1N1 appears to be mild so far with many infected people recovering even without treatment, the H5N1 has a mortality rate of between 60 to 70 percent.
Experts are fearful about the emergence of a hybrid which combines the killing power of the H5N1 with the efficient transmissibility of H1N1. H5N1 is believed to be endemic in countries like China, Indonesia, Vietnam and Egypt.
Guan, an expert on both the H5N1 and SARS, has analysed the genetic sequences of the new virus, which is a triple reassortant containing genetic material from swine, human and bird.
He said there was a huge information gap due to a lack of regular surveillance on animal disease.
Each one of the eight gene segments in the new virus has been seen in pigs in the past 10 years, but experts have no clue when this new H1N1 virus strain first appeared and in which animal species it had been incubating, Guan said.
"We know when each gene segment appeared, but we don't know when this strain first appeared, there is an information gap of about five to 10 years, from 1999 to 2009. If there was regular surveillance, we would know when this virus came about," he said.
"We don't know if this reassortment happened in pigs or human ... It's likely to have come from pigs because all the segments have been found in pigs, but we can't be 100 percent sure."
Guan backed stringent moves taken by some governments to keep the virus at bay, such as quarantining.
"They are useful because we are now fighting for time to develop vaccines and antivirals, which will then minimise its impact on people (over the longer term)," he said.
"Already it appears to more virulent than seasonal flu because it is killing younger people and it appears to have higher mortality than seasonal flu, so it doesn't make sense to treat this like seasonal flu."
Seasonal flu kills about 250,000 to 500,000 people annually with a fatality rate of less than 0.1 percent.
A study published in Science on Monday estimated that the new H1N1 flu virus has a case fatality ratio of 0.4 percent based on confirmed and suspected deaths. (Editing by Jeremy Laurence)
Another cautionary note via John Robb's blog:
WHO The new H1N1 flu virus could still mutate into a more virulent form..
The 1918 influenza pandemic -- which killed tens of millions of people -- began mild and returned within six months in a much more lethal form, it said. The 1968 pandemic began relatively mild, with sporadic cases prior to the first wave, and remained mild in its second wave in most, but not all countries, it said.
Seasonal flu has a so-called "secondary attack rate" -- the percentage of contacts who catch it from an infected person -- of between 5 and 15 percent, according to the WHO. Current estimates of the secondary attack rate of H1N1 range from 22 to 33 percent.
The overall severity of a pandemic is further influenced by the tendency of pandemics to encircle the globe in at least two, sometimes three, waves.. [likely more given interconnection]