Influenza - Evolutionary Dynamics of Influenza
Joshua B. Plotkin, University of Pennsylvania
Influenza viruses infect nearly one-fifth of the human population each year. As common as influenza is, many mysteries remain unresolved about influenza’s molecular biology, evolution, and epidemiology. Aside from their importance to our understanding of viral evolution and ecology, questions about influenza biology have immediate implications for public health – especially in light of the devastating ‘Spanish Flu’ pandemic of 1918, which killed tens of millions people worldwide. Due to the confluence of theoreticians and experimentalists working in co-ordination, influenza research is proceeding at a dramatic rate – making it an ideal topic for this Frontiers meeting.
Influenza infections, which affect both mammals and birds, are caused by a small RNA virus. Influenza viruses evolve more rapidly than virtually all other life forms. Over the past three decades, roughly one-third of the amino acids in the virus’ primary surface protein have undergone substitutions – the equivalent of millions of years worth of evolution in a typical mammalian protein. This remarkable rate of evolution is caused by continual selection for novel variants: because one strain of influenza infects such a large proportion of the human population each year, and because such individuals retain lifelong immunity to their infecting strain, novel antigenic variants that can escape host immunity are selectively advantageous each
Aside from the continual evolutionary changes that occur every year, influenza viruses also periodically experience dramatic evolutionary ‘shifts.’ Such shifts, which are associated with global pandemics, have occurred three times during the 20th century. These dramatic evolutionary shifts are caused by importing a novel viral strain from the avian reservoir into the human host.
The presentations in this session will address questions about influenza evolution over both short and long timescales. Dr. Koelle will discuss a mathematical model that helps us to understand the how the year-to-year patterns of influenza viral evolution are shaped by natural selection. Such research is critically important for helping us to control annual epidemics. Dr. Shinya, by contrast, will discuss experimental work on the molecular mechanism that allow avian viruses to adapt to human hosts. Such research is critically important for our understanding of the rare pandemic events caused by avian importation.
Both presentations highlight the important fact that the study of evolution is not confined to dinosaurs collected in museums. Instead, evolutionary dynamics are ongoing at all scales of biological organization and, in the case of viruses, these dynamics have significant consequences for human health.
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