Probe launched amid flu pandemic fears
http://www.reuters.co.uk/newsPackage...3§ion=news
SINGAPORE (Reuters) - Flu outbreaks have killed tens of millions of people around the globe over the past century, and scientists are investigating if the deaths of three people in Vietnam from bird flu could be the start of a new pandemic.
In most pandemics, animals such as chickens, pigs or even cows have played a role in creating deadly new strains of influenza viruses for which humans have no immunity.
That is what is alarming scientists in Asia after an outbreak of bird flu has killed millions of poultry in Vietnam, South Korea and Japan. The World Health Organisation says 18 people in Vietnam are suspected to have been infected with bird flu, including the three confirmed infections.
But the WHO stresses there is a lack of evidence of human-to-human transmission in Vietnam. The case resembles an outbreak of bird flu in Hong Kong in 1997 when 18 people were infected with avian influenza virus A (H5N1), six of whom died.
That outbreak did not spread because the virus could not pass from one human to another. The slaughter of 1.5 million chickens in the crowded city also prevented more deaths of people.
The danger is when a new virus can cross from person to person. Animals play a key role here because they become breeding grounds for new strains of flu that contain changes in the genetic structure that the human immune system cannot recognise.
According to the science journal Nature, flu viruses originate in wild birds and are thought to become lethal when they cross into poultry or pigs. In cells infected with another flu variety, the viruses pick up genes that enable them to infect humans.
This can also happen, it is thought, in cows.
COUGHING PIGS
According to the U.S. Centres for Disease Control and Prevention, pigs can be infected with human and avian influenza viruses in addition to swine influenza viruses. Infected pigs get symptoms similar to humans, such as cough, fever and runny nose.
Because pigs are susceptible to a variety of flu viruses, they potentially may be infected with viruses from different species, such as ducks and humans, at the same time. If this happens, it is possible for the genes of these viruses to mix and create a new virus.
In Vietnam, hundreds of pigs have also died of flu.
Dr Veronica Chan, head of the microbiology and parasitology department at the University of the Philippines' College of Medicine, said on Wednesday humans would have no protection against a new strain of flu.
"We should worry. It kills. It kills," she told Reuters.
Scientists say major flu pandemics occur every 30-35 years. The deadliest in the past century was the Spanish Flu pandemic of 1918-19 that killed between 20 million and 50 million people worldwide, including 500,000 in the United States. The exact source of this virulent strain is unknown but is thought to have been wild birds.
The virus behind the last major flu outbreak, the Hong Kong flu pandemic of 1968, is thought to have originated with wild aquatic birds such as ducks. Nature journal reported last year that the next killer influenza strain might leap directly from ducks to humans.
Influenza strains in domestic ducks have already acquired genes from poultry viruses, researchers found, and may have the potential to invade human cells.
"It's getting closer to one that can spread," said influenza expert Robert Lamb of Northwestern University in Evanston, Illinois, in a June 5, 2003, report in Nature.
The viruses, known as H9N2, probably jumped from wild birds into poultry, swapped genes with influenza strains there, and then migrated back into ducks, Nature said.
The WHO and other major health bodies have sent experts to Vietnam to investigate the latest outbreak and how it is spreading. They will be looking closely at whether wild birds have spread the avian flu virus around the region.