Swine flu virus H1N1: a threat to human health

Indian Journal of Microbiology, 2009

“Survival of the fittest” is an old axiom laid down by the great evolutionist Charles Darwin and microorganisms seem to have exploited this statement to a great extent. The ability of viruses to adapt themselves to the changing environment has made it possible to inhabit itself in this vast world for the past millions of years. Experts are well versed with the fact that influenza viruses have the capability to trade genetic components from one to the other within animal and human population. In mid April 2009, the Centers for Disease Control and Prevention and the World Health Organization had recognized a dramatic increase in number of influenza cases. These current 2009 infections were found to be caused by a new strain of influenza type A H1N1 virus which is a re-assortment of several strains of influenza viruses commonly infecting human, avian, and swine population. This evolution is quite dependent on swine population which acts as a main reservoir for the reassortment event in virus. With the current rate of progress and the efforts of heath authorities worldwide, we have still not lost the race against fighting this virus. This article gives an insight to the probable source of origin and the evolutionary progress it has gone through that makes it a potential threat in the future, the current scenario and the possible measures that may be explored to further strengthen the war against pandemic.

Annals of Thoracic Medicine, 2009

The causal agent, in fact, is a swine-origin influenza A (H1N1) virus (S-OIV) that is characterized by a unique combination of gene segments that has not been previously identifi ed among human or swine infl uenza A viruses. Actually, the new H1N1 virus appears to be a mixture of avian, porcine, and human infl uenza RNA. Genomic analysis indicates that it is closely related to common reassortant swine infl uenza A viruses that have been isolated in North America, Europe, and Asia in the last 20 years. [4-6] Historically, there have been four to five pandemics of infl uenza during the 20 th century, which have occurred at intervals of 9-39 years. The 1918 pandemic, caused by worldwide spread of a human influenza A (H1N1) virus, was responsible for 40-50 million deaths. An estimated 4.9 million excess deaths, representing 2% of the population, occurred in India alone. [7] After the pandemic subsided, sporadic cases of human infl uenza H1N1 continued to occur worldwide. H1N1 then mysteriously disappeared in 1957, likely due to both competition with the emerging pandemic H2N2 strain as well as the development of immunity to H1N1 among populations. On January 1976, an outbreak of a respiratory The infl uenza pandemic the world was waiting for may have arrived on April 2009, although to date its virulence appears to be no greater than that of seasonal infl uenza. Mexico was the fi rst country where there was a sharp increase in reports of patients requiring hospitalization for pneumonia and an unusual series of deaths, leading to the suspicion that a new infl uenza virus strain was in circulation. During the same period, offi cials at the Centres for Disease Control and Prevention (CDC), Atlanta, uncovered two cases of infl uenza, the so-called 'swine infl uenza,' that were clearly due to a novel strain; the two patients were children living in neighbouring

2010

Influenza virus has caused major global epidemics since 1918. Although this commonly circulating viral strain is not virulent enough to cause mortality, but the re-assortment of viral genome to mutate at a very high rate can lead to the emergence of a highly virulent strain that may lead to next pandemics. Swine flu is an example of re-assortment of two viruses in pig causing thousands of deaths in the whole world especially in the United States of America by zoonotic jumps. This review addresses the biological and epidemiological aspects of swine flu virus and efforts to have a control on the virus globally.

Science (New York, N.Y.), 2012

Causative agent Swine flu is a respiratory disease caused by a strain of the influenza virus type A. These are RNA viruses have an envelope surface antigen hemagglutinin that is responsible for the infectivity. It attaches specifically to a receptor on the erythrocytes and other host cells. Some influenza viruses have an enzyme called neuraminidase which helps the virus penetrate the mucus layer protecting the respiratory epithelium. The neuraminidase enzyme plays a role in the buddding of the new virus particles from the infected cells. Influenza A virus strains caused three major global epidemics during the 20th century: the spanish flu in 1918, Asian flu in 1957 and Hong kong flu in 1968-69. These pandemics were caused by strains of Influenza A virus that had undergone major genetic changes and for which the population did not possess significant immunity. Influenza B virus also undergoes antigenic changes but less extremly and at a slower rate than influenza A virus. Influenza C virus are rarely recognised. Antigenic Variation Antigenic variation occurs by two processes, antigenic drift and antigenic shift. The antigenic drift results from mutations in genes that code for haemaggluttinin and neuraminidase. Such mutations change the configuration of the part of antigenic

2009

Cold Spring Harbor Perspectives in Medicine

Influenza A viruses (IAVs) are the causative agents of one of the most important viral respiratory diseases in pigs and humans. Human and swine IAV are prone to interspecies transmission, leading to regular incursions from human to pig and vice versa. This bidirectional transmission of IAV has heavily influenced the evolutionary history of IAV in both species. Transmission of distinct human seasonal lineages to pigs, followed by sustained within-host transmission and rapid adaptation and evolution, represent a considerable challenge for pig health and production. Consequently, although only subtypes of H1N1, H1N2, and H3N2 are endemic in swine around the world, extensive diversity can be found in the hemagglutinin (HA) and neuraminidase (NA) genes, as well as the remaining six genes. We review the complicated global epidemiology of IAV in swine and the inextricably entangled implications for public health and influenza pandemic planning.

The Canadian veterinary journal. La revue vétérinaire canadienne, 2010

In the spring of 2009, a new human influenza A H1N1 virus emerged in Mexico and the United States. The strain was referred to as "swine flu" as it has strong similarities with current circulating swine influenza viruses, although the first outbreak on a swine farm was recorded more than 2 mo following the first human reports. This new strain, designated as pandemic (H1N1) 2009, has shown the ability to spread amongst the human population and can be found on all continents. The way influenza viruses and specifically this influenza A pandemic (H1N1) 2009 virus evolve is described in this manuscript.

mBio, 2010

Epidemiologic observations that have been made in the context of the current pandemic influenza virus include a stable virulence phenotype and a lack of propensity to reassort with seasonal strains. In an attempt to determine whether either of these observations could change in the future, we coinfected differentiated human airway cells with seasonal oseltamivir-resistant A/New Jersey/15/07 and pandemic A/Tennessee/1-560/09 (H1N1) viruses in three ratios (10:90, 50:50, and 90:10) and examined the resulting progeny viruses after 10 sequential passages. When the pandemic virus was initially present at multiplicities of infection equal to or greater than those for the seasonal virus, only pandemic virus genotypes were detected. These adapted pandemic strains did, however, contain two nonsynonymous mutations (hemagglutinin K154Q and polymerase acidic protein L295P) that conferred a more virulent phenotype, both in cell cultures and in ferrets, than their parental strains. The polymerase...

For the emergency created by the epidemic of influence of the pigs in Mexico it was correct not to create alarmisms being victims of a bad information. The possibility that the virus arrives in other parts of the world is real as for all the types of influence virus. In order that a strain has a wide distribution, its antigenic characteristics must ensure that it escapes the neutralization of antibodies of the host and of the surrounding population. The discovery of a new, biologic Host-Defense protein, “HDFx”, may provide a unique way to ameliorate and prevent the “cytokine storms” and haemorrhages seen in severe influenza infections. The influenza A virus subtypes H1N1, H1N2 and H3N2 are prevalent in pig populations worldwide. All scientific data point towards swine as the key host species for new human influenza pandemics, which have been suggested to evolve in pigs from viral genes of avian, human and porcine origin. Therefore, it is of major importance torecord the evolution of swine influenza viruses in pigs, and in particular monitor hallmarks of adaptation to humans. The scope of this paper was to increase the understanding of the genetics of Swine Influenza Virus (SIV), and to investigate the importance of different viral gene markers in association with differences in pathogenicity of two viruses of H1N2 subtype in pigs. The results from this study demonstrate, for the first time, natural reassortment in H1N2 viruses in the pig populations of Sweden as well as in india. So the outbreaks will happen with those strains that have dominant antigens that fit the deficiency, or better, the abscences of antibody in the population. It seems, in conclusion that the flu virus showes an ability and an aptitude for survival built on the possibility of émergence of new models that allow the virus being confused easily through populations still partly immune to previous antigenic forms. According to this view, the changes in the influenza A can be designed in single meaning, in the context of a principle and of an evelutionary progress, from Burnet said immunological drift or steering immunology. The antiviral drugs (inhibitors of the neuraminidasis, receptor of the virus surface) should be assumed within 48 hours by the appearance of the influence symptoms and for the subjects that have had a close contact with people infected by the flu virus. The vaccination against the influence is the most effective method to prevent the illness. From the moment that we find the isolation of a new flu virus, we must wait for the preparation of a new specific vaccine that will be ready for the next influence season in Autumn. Keywords: Virus; Influenza; Flu; Avian; Swine