In an article entitled “Further evidence for infection of pigs with human-like H1N1 influenza viruses in China” by Hai Yu et al which appeared in the 3rd of January 2009 issue of Virus Research journal, a detailed molecular virology study has been reported which gives important scientific explanation that can help explain the current re-emergence of human like H1N1 influenza virus, and why pigs are important reservoirs of the influenza infection.
Swine influenza is an acute respiratory disease caused by influenza virus which can lead to clinical manifestation including fever and acute respiratory distress in pigs, birds and even humans (Brown, 2000). The disease is common in China which has been regarded as the historic epicenter of the pandemic influenza viruses (Shortridge and Stuart-Harris, 1982).
According to Ito et al (1998) and Peiris et al (2001), “the tracheal epilithium in pigs expresses receptors for both humans and avian influenza viruses, and this provides a biological basis for the susceptibility of pigs to both avian and human influenza viruses”. Pigs therefore act as important reservoirs of the influenza infection as they offer opportunity for human avian and human viral genetic “mixing” through co-infections, replications, and re-assortment which can also lead to inter-species transmissions (Brown, 2000; Landolt et al., 2003).
In the study by Hai Yu et al (2009), various molecular virology methods were used for understanding the molecular epidemiology of the influenza virus and unraveling the dynamics of the of the influenza zoonosis. The influenza viruses were isolated from pigs by inoculation and culture in embryonated chicken eggs (Yu et al, 2007). Viral RNA was then extracted from infected allantoic fluids and then reverse transcription polymerase chain reaction (RT-PCR) done before cloning the transcripts into appropriate cloning vector (PMD18-T Vector), and then sequencing of the viral genes before phylogenetic analysis using bioinformatics tools (Hai Yu et al, 2009).
In the study under review, serum samples were also collected from pigs and serological analysis was done using haemagglutination inhibition (HAI) tests (WHO, 2002), and neutralizing antibody immunoassays for determination of cytopathic effects of the viruses (Hai Yu et al, 2009). The study reported for the first time, “the co-existence of recent (about 2000) human-like and early (1980s) human-like swine H1N1 influenza viruses in pigs in China” (Hai Yu et al, 2009). This was shown by the sequence homology assays, and the phylogenetic relationship and lineage analysis which detected the existence of human, classical swine, and avian strains of the influenza virus in the pigs. Molecular analysis for the determination of antigenic sites detected the interspecies transmission of H1N1 influenza virus from human to pigs and also showed interspecies conserved glycosylation sites in the swine viruses. Glycosylation sites analysis was important in understanding how new influenza virus strains are generated in the pigs (Schulze, 1997; Hai Yu et al, 2009). The study also showed that the “human-like H1N1 swine influenza virus might sporadically infect pigs in China” as revealed by the serological surveillance results (Hai Yu et al, 2009).
Molecular virology research as reported in the article by Hai Yu et al (2009) is important in the field of biology as it can help in understanding the fine mechanisms of molecular evolution which can help in understanding the speciation process through generation of genetic diversity, and adaptation to environmental conditions. In the field of biomedicine, the research can help us understand how disease causing pathogens (such as viruses, bacteria and parasites) adapt to the host organisms in which they cause diseases. The research can also help in detection of antigenic sites which can help in vaccine development studies.
The kind of molecular research, as reported by Hai Yu et al (2009) can have several applications. First, as has been seen in the study under review, it can help in understanding the molecular epidemiology of infectious disease pathogens and also help in their surveillance and designing control strategies in the affected populations. Secondly, the techniques are highly transferable and can be used for developing diagnostic tools (both molecular and immunological) for detection of disease pathogens. Thirdly, the molecular PCR amplification, sequencing and cloning including the associated isolation and culture techniques, can be used for similar studies or research of other infectious diseases and even for non disease related studies of animals and plants.
References
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Hai Yu, Yan, J. Z., Guo-Xi, L., Gui-Hong, Z., Hui-Li, L., Li-Ping, Y., Ming, L., Guang- Zhi, T. (2009). Further evidence for infection of pigs with human-like H1N1 influenza viruses in China. Virus research, 140, 85-90.
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Yu, H., Zhang, G. H., Hua, R. H., Zhang, Q., Liu, T. Q., Liao, M., Tong, G. Z. (2007). Isolation and genetic analysis of human original H1N1 and H3N2 influenza viruses from pigs in China. Biochem. Biophys. Res. Commun. 365, 91-96.