BANFF, Alta. – The ongoing H1N1 pandemic was an important development in giving researchers new insight into the virus.
Influenza viruses affect many species with varying degrees of severity. With H1N1, thousands of people have died since it was detected in the spring of 2009, yet infected hogs suffered minimal effects.
Veterinarian Marie Gramer from the University of Minnesota’s veterinary diagnostic laboratory told people at the Banff Pork Seminar Jan. 20 that although researchers had been aware for 20 years that pigs could be infected with human influenza, they didn’t know how severe it could become.
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“We knew some things about influenza in pigs but they were overlooked by veterinarians, human researchers, influenza researchers,” Gramer said.“We overlooked it because it didn’t seem to spread or we weren’t able to detect it.”
She said pigs are like mixing vessels for viruses from many sources that can combine with others in a process called reassortment.
“Pigs have these receptors in their respiratory tracts in their nose, lungs, trachea and deep down into their lungs, that can bind all the influenza viruses that are out there,” she said.
Other mammals also have this trait, such as the North American skunk, raccoons and Persian leopards.
“Humans can be mixing vessels as well,” she said.
She said people working with poultry and pigs should be vaccinated.
The influenza virus appears as a segmented single strand of RNA and consists of influenza A, influenza B and influenza C.
Swine influenza virus is an influenza A, which causes disease in animals, birds and humans. Influenza B appears to cause disease only in humans, while influenza C viruses are rare. These RNA viruses are able to mutate, can live for a long time and are hard to control.
The influenza A virus genome has eight RNA gene segments, which can break into cells and replicate its RNA to provide mixed influenza virus.
Mistakes can arise in the gene sequence during this blending, resulting in numerous variants within each subtype due to genetic drift.
These mutations can occur within each gene or in a genetic shift. It is what scientists call a reassortment of genes between viruses infecting the same host cell.
“A reassortment usually causes disease because it is a dramatic change for the immune system to respond to that,” Gramer said.
Last year’s H1N1 pandemic virus was a mixture of bird, human and swine virus. The virus had accumulated changes in several genes that made it capable of spreading easily from human to human and from human to pig. Scientists are unable to definitively identify why, when and where these changes occur.
