Connected World Gives Viruses The Edge

“The findings also suggest that as human activity makes the world more connected, natural selection will favour more virulent and dangerous parasites.”

– This quote from the article text below is no surprise to me or to anyone who has looked at the logic of how contagious diseases spread.   You pack more and more people together and the situation begins to favors more and more virulent diseases.   The Black Death in Europe was, perhaps, the first concrete demonstration of this.  The world today is ripe and getting riper for this sort of thing.   We’ve been extremely lucky that some of the very nasty things around like Ebola have not thus far gotten loose in a population center.

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That’s one conclusion from a new study that looked at how virulence evolves in parasites. The research examined whether parasites evolve to be more or less aggressive depending on whether they are closely connected to their hosts or scattered among more isolated clusters of hosts.

The research was led by Geoff Wild, an NSERC-funded mathematician at the University of Western Ontario, with colleagues from the University of Edinburgh.

“Our study follows up on some recent findings that suggest that reduced dispersal of parasites across scattered host clusters favours the evolution of parasites with lower virulence – in the case of influenza, for example, a milder, possibly less deadly, case of flu,” said Dr. Wild.

“Some researchers had contended from this that the parasites were evolving to support the overall fitness of the group,” he added. “The argument for adaptation at the group level is that the parasites become more prudent to prevent overexploitation and hence to avoid causing the extinction of the local host population.”

However, Dr. Wild and his colleagues were not convinced that Darwinian theory – so successful in providing explanations based on the notion that adaptation maximizes individual fitness – was ready for such a major makeover.

The researchers decided to move the arguments from words to harder science. Together they developed a formal mathematical model that incorporated variable patch sizes and the host parasite population dynamics. It was then run to determine the underlying evolutionary mechanisms, the results of which were published in the Nature paper.


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