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| The discovery of avian flu genes in swine has provided additional evidence to the theory that swine is a potential "mixing vessel" for influenza viruses |
The new strain, H2N3, belongs to the H2 influenza virus group responsible for infecting humans during a 1957 pandemic.
In 2006, Dr Marie Gramer at the University of Minnesota identified H2N3 in two groups of pigs at facilities that used pond water frequented by migrating water fowl. It was the first time this strain, which is related to a strain of H2N3 previously identified in mallard ducks, was found in a mammal.
Swine H2N3 contains segments from avian H2 and N3 genes and the common swine influenza virus. The segments combined and mutated, enabling it to infect swine, as well as mice and ferrets.
ARS veterinarian Dr Juergen Richt tells Animal Pharm that the critical gene for the entry of the virus into the host cells is the hemagglutinin gene (HA).
"The HA gene of the H2N3 virus is derived from an avian influenza virus," he says. "We obviously know that the H2N3 virus with the avian genes was able to enter pigs. Once this event occurred, the virus began to mutate, allowing for adaptation to the swine host.
"Mutations known to be important for host specificity were found in the swine H2 gene, which were different from the purely avian H2 gene. Mutations were also identified in other viral genes of the swine H2N3 when compared to purely avian viruses; however we do not know their role in the adaptation to the pig."
The discovery of avian flu genes in swine has provided additional evidence to the theory that swine is a potential "mixing vessel" for influenza viruses.
"The 'mixing vessel' theory is based on the fact that the pig has receptors for both avian and mammalian influenza viruses," Dr Richt says. "Since both groups of influenza viruses can replicate in the pig, there is a chance that individual influenza virus segments (genes) can be 'mixed' (a process also known as 'reassortment') if avian and mammalian viruses replicate at the same time in an individual pig. Therefore, the pig and other animals (quail, for example) which are susceptible to infection and replication by avian and mammalian influenza viruses are called 'mixing vessels'."
Dr Richt adds that these findings emphasize the need for careful monitoring and collaboration between human and veterinary diagnostic and research laboratories to better understand the potential of H2N3 or other emerging influenza viruses. He adds that surface water should also be monitored since it could be considered a risk factor for exposure of pigs to avian influenza viruses and a potential source of introducing these viruses into swine herds.
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