Scientists warn of lethal consequences if swine and bird flu mix

BIRD flu kills more than 60% of its human victims, but doesn’t easily pass from person to person.

Swine flu can be spread with a sneeze or handshake, but kills only a small fraction of the people it infects.

So what happens if they mix?

This is the scenario that has some scientists worried – the two viruses meet, possibly in Asia where bird flu is endemic, and combine into a new bug that is both highly contagious and lethal and can spread around the world.

Scientists are unsure how likely this possibility is, but note that the new swine flu strain – a never-before-seen mixture of pig, human and bird viruses – is especially adept at snatching evolutionarily advantageous genetic material from other flu viruses.

“This particular virus seems to have this unique ability to pick up other genes,” said leading virologist Dr Robert Webster, whose team discovered an ancestor of the current flu virus at a North Carolina pig farm in 1998.

The current swine flu strain, H1N1, has affected more than 2,300 people in 24 countries. While people can catch bird flu from birds, the bird flu virus – H5N1 – does not easily jump from person to person. It has killed at least 258 people worldwide since it began to ravage poultry stocks in Asia in late 2003.

The World Health Organisation reported two new human cases of bird flu on Wednesday. One patient is recovering in Egypt, while another died in Vietnam.

“Do not drop the ball in monitoring H5N1,” WHO director-general Margaret Chan told a meeting of Asia’s top health officials in Bangkok yesterday by video link. “We have no idea how H5N1 will behave under the pressure of a pandemic.”

Experts have long feared that bird flu could mutate into a form that spreads easily among people.

The past three flu pandemics – the 1918 Spanish flu, the 1957-58 Asian flu and the Hong Kong flu of 1968-69 – were all linked to birds, though some scientists believe pigs also played a role in 1918.

Webster, who works at St Jude’s Children’s Research Hospital in Memphis, Tennessee, said bird flu should be a worry now. Bird flu is endemic in parts of Asia and Africa, and cases of swine flu have occurred in South Korea and Hong Kong.

“My great worry is that when this H1N1 virus gets into the epicentres for H5N1 in Indonesia, Egypt and China, we may have real problems,” he said. “We have to watch what’s going on very diligently now.”

Malik Peiris, a flu expert at Hong Kong University, said the more immediate worry is that swine flu will mix with regular flu viruses, as flu season begins in the southern hemisphere.

Peiris said there are indications that scenario is possible. He noted that the swine flu virus jumped from a farm worker in Canada and infected about 220 pigs. The worker and pigs recovered, but the incident showed how easily the virus can leap to a different species.

“It will get passed back to pigs and then probably go from pigs to humans,” Peiris said. “So there would be opportunities for further reassortments to occur with viruses in pigs.”

Dr Webster has done groundbreaking work on both swine and bird flus in his 40-year career. He is closely involved in the global effort to analyse what the virus might do next. It has killed 42 people in Mexico and two in Texas.

Dr Webster said underestimating the swine flu virus would be a huge mistake.

“This H1N1 hasn’t been overblown. It’s a puppy, it’s an infant, and it’s growing... What we have to do is to watch it, and it may become a wimp and disappear, or it may become nasty.”