From birds to pigs to humans

The difference between preparedness and paranoia over the Mexican swine flu outbreak could be as small as a cake of soap, according to a leading Perth virologist.

Murdoch University’s Head of Veterinary Biology and Biomedical Sciences Professor Graham Wilcox said the latest strain appeared to be a mix of influenza viruses, which has been detected previously in birds, pigs and humans.

He recommended prevention with the same good hygiene used to stop the spread of any infectious disease, including the winter flu virus.

"This virus is being spread from Mexico to other countries by people who have become infected in Mexico," Professor Wilcox said.

"It has the potential to become widespread in several countries worldwide – that is, to become a pandemic."

He said there was not much information available at this point following the Mexico outbreak, with some reports providing conflicting evidence, "but it is logical to conclude that it has arisen originally from a virus present in waterbirds, the ultimate source of all influenza viruses."

Having infected pigs, with some exchange of genetic information with viruses that infect pigs (in Mexico), this modified avian-pig virus has then infected humans.

There has then been some further exchange of genetic information with the H1N1 influenza viruses that are currently circulating in humans, and have done for many years.

"The new virus has the ability to be transmitted directly from human to human unlike the avian H5N1 strain present in Asia that is transmitted directly from birds to humans and does not normally undergo transmission from one person to another," he said.

"There is no evidence that it causes disease in pigs and its designation as a ‘pig’ virus is probably unfortunate."

The contagious disease identified in Mexico has been reported to be slowing in the nation hardest hit, although the World Health Organisation has cautioned there is no evidence the worst of the global outbreak is over.

(Source: Murdoch University: May 2009)