Dating the emergence of pandemic influenza
The study's findings suggest people are made critically ill, or even killed, by their own immune response.A hallmark of pandemic flu throughout history, including the 2009 H1N1 pandemic, has been its ability to make healthy young and middle-aged adults seriously ill and even kill this population in disproportionate numbers. 5 in Nature Medicine, Vanderbilt University Medical Center researchers provide a possible explanation for this alarming phenomenon of pandemic flu., suggests that all three influenza pandemics–1918, 1957, and 1968–were the result of stepwise genetic integrations of both avian and mammalian genes over a number of years, ultimately creating the more virulent virus strains.And although the research was done before the emergence of the current H1N1 “swine flu” strain, the scientists’ conclusions are relevant, showing that the current virus follows the same historical pattern.To determine factors involved in the zoonotic origin of the 1957 pandemic, we performed analyses on genetic sequences of 175 newly sequenced human and avian H2N2 virus isolates and all publicly available influenza virus genomes.Influenza A viruses are ecologically successful pathogens that infect a wide range of host species and that have periodically emerged in humans to cause pandemics (1).
The tall and burly Warren County, TN, ambulance worker -- a 30-year-old, father of three young children -- broke down and hugged some of the nurses he recognized.Nucleotide sequences of each gene segment were initially aligned using MAFFT (6) and then manually corrected and assembled to include only coding regions.To determine the most closely related avian and human clades, maximum likelihood (ML) trees were inferred based on nucleotide alignments using the program Fast Tree version 2.1.5 (7) under the generalized time-reversible (GTR) model with gamma-distributed rates among sites (GTR Γ) (see Fig. The ML trees were used to select the avian viruses most closely related to the human H2N2 viruses for further analysis.But there are no known precursor viruses to the 1918 strain, so the computational results can only infer the time of interspecies transmission, based on known patterns of genetic evolution.The genetic data itself was derived from virus strains that have evolved since 1918.