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Piggybacking pandemics?

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Are you ready for another pandemic?  Not later, after this one is over—right now. Because it is a possibility. Call them piggybacking pandemics.

Because it starts with pigs.

In a recent paper in the Proceedings of the National Academy of Science, researchers describe a group (termed “G4”) of H1N1 swine flu viruses that have the potential to jump to people. These avian-like H1N1 viruses are now the most common type of influenza circulating among pigs in China. According to the report, they have a perfect storm of characteristics to cause infections in humans, including the ability to spread through respiratory droplets via direct contact with infected animals and the ability to replicate easily in human lungs, making G4 a potential pandemic concern.

Potential is the key word.

Robert Webster, PhD, MSc, DSc, a pioneering influenza researcher, told Science Magazine, “We just do not know a pandemic is going to occur until the damn thing occurs. Will this one do it? God knows.”

Pigs are like Petri dishes for influenza because they can host both mammalian and avian flu viruses.

When multiple strains of influenza viruses infect the same pig, they can easily swap genes. This process is known as reassortment, which occurs when two different influenza viruses coinfect a cell. The viral diversity generated through reassortment is huge and plays an important role in the evolution of influenza viruses. The G4 variants are of particular concern because they’re essentially avian viruses with bits of mammalian flu viruses mixed in, and humans have no natural immunity to avian strains.

The new G4 viruses include genes from three distinct influenza strains: a strain similar to avian viruses present in European and Asian birds; a North American strain that has genes from avian, human, and pig influenza viruses; and the H1N1 strain that caused the 2009 swine flu pandemic—a strain researchers first detected in the US.

That pandemic wasn’t as deadly as initially feared—many older people had some immunity to it because it was similar to previous strains. But the authors of the new paper say that G4’s inclusion of genes from the 2009 H1N1 pandemic “may promote the virus adaptation” that leads to human-to-human transmission.

While only three cases of human infection with G4 viruses have ever been reported, the researchers found that 10% of the Chinese swine workers they tested showed evidence of previous infections with similar viruses, indicating that human infection is more common than previously suspected.

The good news is, the US Centers for Disease Control and Prevention note that there are no reports of G4 viruses spreading from person to person (a characteristic required in order for a pandemic to occur), and that G4 viruses have not been detected in pigs or people in the US. However, the agency acknowledges that the G4 viruses have “pandemic potential” and is taking steps to prepare against what it calls an “emerging public health threat.”

So basically, don’t worry, but be aware. Because pandemics don’t take a number.

Photo credit: © iStock/t-lorien