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Genetic and pathobiologic characterization of pandemic H1N1 2009 influenza viruses from a naturally infected swine herd.

ABSTRACT: Since its initial identification in Mexico and the United States, concerns have been raised that the novel H1N1 influenza virus might cause a pandemic of severity comparable to that of the 1918 pandemic. In late April 2009, viruses phylogenetically related to pandemic H1N1 influenza virus were isolated from an outbreak on a Canadian pig farm. This outbreak also had epidemiological links to a suspected human case. Experimental infections carried out in pigs using one of the swine isolates from this outbreak and the human isolate A/Mexico/InDRE4487/2009 showed differences in virus recovery from the lower respiratory tract. Virus was consistently isolated from the lungs of pigs infected with A/Mexico/InDRE4487/2009, while only one pig infected with A/swine/Alberta/OTH-33-8/2008 yielded live virus from the lung, despite comparable amounts of viral RNA and antigen in both groups of pigs. Clinical disease resembled other influenza virus infections in swine, albeit with somewhat prolonged virus antigen detection and delayed viral-RNA clearance from the lungs. There was also a noteworthy amount of genotypic variability among the viruses isolated from the pigs on the farm. This, along with the somewhat irregular pathobiological characteristics observed in experimentally infected animals, suggests that although the virus may be of swine origin, significant viral evolution may still be ongoing.

SUBMITTER: Weingartl HM

PROVIDER: S-EPMC2820904 | biostudies-literature | 2010 Mar

REPOSITORIES: biostudies-literature

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Genetic and pathobiologic characterization of pandemic H1N1 2009 influenza viruses from a naturally infected swine herd.

Weingartl Hana M HM Berhane Yohannes Y Hisanaga Tamiko T Neufeld James J Kehler Helen H Emburry-Hyatt Carissa C Hooper-McGreevy Kathleen K Kasloff Samantha S Dalman Brett B Bystrom Jan J Alexandersen Soren S Li Yan Y Pasick John J

Journal of virology 20091216 5

Since its initial identification in Mexico and the United States, concerns have been raised that the novel H1N1 influenza virus might cause a pandemic of severity comparable to that of the 1918 pandemic. In late April 2009, viruses phylogenetically related to pandemic H1N1 influenza virus were isolated from an outbreak on a Canadian pig farm. This outbreak also had epidemiological links to a suspected human case. Experimental infections carried out in pigs using one of the swine isolates from th ...[more]

PMID: 20015998

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Project description:Human-to-swine transmission of seasonal influenza viruses has led to sustained human-like influenza viruses circulating in the U.S. swine population. While some reverse zoonotic-origin viruses adapt and become enzootic in swine, nascent reverse zoonoses may result in virus detections that are difficult to classify as "swine-origin" or "human-origin" due to the genetic similarity of circulating viruses. This is the case for human-origin influenza A(H1N1) pandemic 2009 (pdm09) viruses detected in pigs following numerous reverse zoonosis events since the 2009 pandemic. We report the identification of two human infections with A(H1N1)pdm09 viruses originating from swine hosts and classify them as "swine-origin" variant influenza viruses based on phylogenetic analysis and sequence comparison methods. Phylogenetic analyses of viral genomes from two cases revealed these viruses were reassortants containing A(H1N1)pdm09 hemagglutinin (HA) and neuraminidase (NA) genes with genetic combinations derived from the triple reassortant internal gene cassette. Follow-up investigations determined that one individual had direct exposure to swine in the week preceding illness onset, while another did not report swine exposure. The swine-origin A(H1N1) variant cases were resolved by full genome sequence comparison of the variant viruses to swine influenza genomes. However, if reassortment does not result in the acquisition of swine-associated genes and swine virus genomic sequences are not available from the exposure source, future cases may not be discernible. We have developed a pipeline that performs maximum likelihood analyses, a k-mer-based set difference algorithm, and random forest algorithms to identify swine-associated sequences in the hemagglutinin gene to differentiate between human-origin and swine-origin A(H1N1)pdm09 viruses.IMPORTANCE Influenza virus infects a wide range of hosts, resulting in illnesses that vary from asymptomatic cases to severe pneumonia and death. Viral transfer can occur between human and nonhuman hosts, resulting in human and nonhuman origin viruses circulating in novel hosts. In this work, we have identified the first case of a swine-origin influenza A(H1N1)pdm09 virus resulting in a human infection. This shows that these viruses not only circulate in swine hosts, but are continuing to evolve and distinguish themselves from previously circulating human-origin influenza viruses. The development of techniques for distinguishing human-origin and swine-origin viruses are necessary for the continued surveillance of influenza viruses. We show that unique genetic signatures can differentiate circulating swine-associated strains from circulating human-associated strains of influenza A(H1N1)pdm09, and these signatures can be used to enhance surveillance of swine-origin influenza.

Dataset Information

Genetic and pathobiologic characterization of pandemic H1N1 2009 influenza viruses from a naturally infected swine herd.

Publications

Genetic and pathobiologic characterization of pandemic H1N1 2009 influenza viruses from a naturally infected swine herd.

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