ARS | Publication request: Identification and Characterization of a Highly Virulent Triple Reassortant H1N1 Swine Influenza Virus in the Midwest of the United States

Submitted to: Virus Genes
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 9, 2009
Publication Date: February 1, 2010
Citation: Ma, W., Vincent, A.L., Lager, K.M., Janke, B.H., Henry, S.C., Rowland, R.R., Hesse, R.A., Richt, J.A. 2010. Identification and Characterization of a Highly Virulent Triple Reassortant H1N1 Swine Influenza Virus in the United States. Virus Genes. 40(1):28-36.

Interpretive Summary: Swine are susceptible to infection with influenza type A viruses. The natural reservoir for influenza A viruses is waterfowl. Occasionally, viruses from wild birds will “jump species” into domestic poultry and mammals, including humans. Sometimes this event will establish a new lineage of influenza virus in the susceptible host, and the virus can transmit between mammalian species. A recent example of this is the emergence of the human 2009 H1N1 pandemic influenza A virus that had a swine origin. Because of the potential for the establishment of new viruses in a species, it is important to maintain a surveillance program for novel influenza viruses in avian and mammalian species. This report characterizes a unique lineage of swine influenza virus found in Kansas in December 2007 that is closely related to a virus that caused a human and swine infection in Ohio August 2007. This virus, like the Ohio virus, is capable of causing significant disease in pigs; however, it is not known if the Kansas virus has infected people. Even though this swine virus is of the H1N1 subtype, it is not closely related to the pandemic H1N1 virus now found in humans. It is not known how this virus moved from Ohio to Kansas, or how widespread this virus may be in the U.S. swine population. This report reinforces the unique relationship between swine and humans for influenza viruses, and the importance of identifying unique swine viruses that may have the potential for human infection.

Technical Abstract: An H1N1 influenza A virus, A/Swine/Kansas/77778/2007 (KS07) was isolated from a herd in Kansas that was suffering severe respiratory disease and 10% mortality. A pig challenge model was developed to evaluate the pathogenicity and transmission capacity of the KS07 virus. The pathogenicity and transmission studies demonstrated the KS07 virus could cause severe disease, had a prolonged shedding period out to 7 days post-infection, and was transmitted efficiently to sentinel animals. The KS07 virus did not cross-react with a panel of H1-specific swine sera raised against recent viruses. Molecular and phylogenic analysis revealed this swine isolate was a triple reassortant virus, similar to an H1N1 virus that infected humans and pigs at a Ohio county fair in August 2007, and is further evidence of reassortment among avian, human and swine influenza viruses. In addition, the finding of this novel virus in Ohio, then in Kansas reveals the apparent dissemination of this virus throughout the national swine herd and the continual need for an influenza virus surveillance program in swine.