Conclusions and Future Perspectives

Abstract

The influenza A virus is most important among the three types of influenza viruses (types A, B and C) that normally cause respiratory disease in human, animals and poultry. The avian and swine influenza A viruses are zoonotic in nature. The genome of influenza viruses is segmented single-stranded RNA of negative polarity. The matrix and nucleoprotein proteins determine type specificity. Influenza A viruses have further been classified into 18 haemagglutinin subtypes and 11 neuraminidase subtypes. Many different factors affect the evolution of influenza viruses which may have a direct effect on their virulence, pathogenicity, immunity, drug resistance etc. The influenza A virus H5N1, Swine flu (H1N1 subtype) virus [SO-IV; H1N1pdm], and H7N9 subtypes have in recent years emerged as a dangerous flu strains that have caused a large number of human deaths. The influenza viruses in human cause seasonal flu every year or sometimes may cause pandemics. The pathogenicity and transmissibility are the main determinants of potential of an emerging viral strain to become a pandemic influenza virus. Virus replication in the endothelium including proteolytic activation of the haemagglutinin, polarity of virus budding, and tissue specific expression of virus receptors appears to play a pivotal role in pathogenesis. The expression of virus pathogenicity is dependent upon the functional integrity of each gene, and on a gene constellation optimal for infection of a given host. Commercial antiviral drugs are available for treatment of the human flu. Commercial vaccines are available in the market against human, equines, swine and avian influenza viruses. The DIVA vaccine strategies for avian influenza viruses are being developed and refined. The current focus is to develop universal vaccine against influenza viruses which should provide broad protective immunity against conserved antigens present in many different subtypes of influenza viruses. Besides the use of antivirals and vaccines, the legislative measures, stringent biosecurity measures, strict quarantine and trade limitations play an important role for the prevention and control of influenza viruses.