It's not where a virus comes from but how it becomes contagious
New technologies allow us to observe cross-species transmission in ways we could not before, but we lack the fundamental understanding of the relationship between virus genetics and transmission in humans to distinguish the next Ebola or HIV from viruses that pose no threat.
Influenza viruses are a microcosm of this process. There are thousands of confirmed instances of humans being infected, sometimes fatally, with non-human flu strains; but only a handful of strains have adapted to cause human epidemics. However, those that do adapt can be devastating, as was the 'Great Influenza' of 1918, which killed 20-100 million people in only a few years. The 1918 flu pandemic and others were likely preceded by multiple instances of animal-to-human transmission of related viruses.
Bottom line: We are the first generation with the tools to observe this pre-pandemic 'viral chatter' between species, but we will be unable to develop any sort of pandemic early warning system until we better understand how the genetics of viruses relate to their ability to transmit in humans. Doing this for influenza could establish the fundamental biological theory needed to identify, and perhaps stop the next HIV or Ebola before it happens.
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