Virologist warns state health workers of swine flu's second wave

As Canadian health officials reported, the world's first case of the swine flu jumped to pigs from a human, probably after a farm worker in the province of Alberta became ill during a trip to Mexico.

"Additional gene reassortment has the potential to change the makeup of the disease," Robertson said.

Pigs are what Robertson called a "prime mixing vessel" for new forms of the flu, including the H1N1 virus, noting that's why the best likely hypothesis among microbiologists is that the new flu is a combination of four strains from swine, birds and humans that started inside a pig.

World Health Organization officials have said that if pigs are infected with a new virus, and some of the swine influenza viruses are circulating, there could be additional reassortments.

"The same is true if a human were co-infected," Robertson said. "We could have a virus reassortment that is slightly different than either of the two parental sources."

Flu bugs, like all life on the planet, never go away, they just become less capable of causing infection, he said.

"That is part of the enigma that is influenza," Robertson said. "It is knowable but not predictable."

At the National Institute for Biological Standards Control in London, where Robertson heads the division of virology, researchers are developing a candidate virus to form a vaccine against swine flu.

Researchers are injecting viruses into hen's eggs, where they grow for two or three days and are then extracted and examined to determine a candidate virus to form a vaccine against swine flu.

The process takes about four weeks as the virus is broken open and its eight genes extract and mixed with harmless lab flu strains to create a range of hybrids.

"If a virus grows really well in the eggs, its a sign that it possesses the right features for a future vaccine, that is that it stimulate immune responses when injected into humans," Robertson said.

So far, growth isn't giving researchers much to go on, he said. When they do, it will present another decision for public health authorities: Should the vaccine manufacturing already under way and likely not be completed until about July shift toward building a new one?"We're doing all we can," Robertson said, "including keeping our fingers crossed."

E-MAIL: jthalman@desnews.com