Zika: Don't panic

Zika, the mosquito-borne virus spreading through the Americas that has been linked to thousands of babies born with underdeveloped brains (microcephaly), is just the latest new disease to spread panic around the world. And wait! News just in that it can be sexually transmitted too!

There is real cause for concern here. The virus is almost bound to spread to the rest of the world, except those parts with winters severe enough to kill off the two species of mosquito that bear it, Aedes aegypti and Aedes albopicti. And these mosquitos are active during the day (unlike the Anopheles mosquitos that spread the malaria parasite), so insecticide-treated bed nets don't offer much protection.

The World Health Organization has declared a global public health emergency, and the media panic is building: first AIDS, now this. We are too many, we travel too much, and new pandemics are nature's retaliation for our many sins. Clearly the apocalypse is upon us. 

Well, no, actually. New diseases have been devastating human populations for at least 3,000 years, but no modern pandemic can be compared to the Antonine Plague of the second century CE, the Justinian Plague of the sixth century, or the Black Death of the 14th century, each of which killed between a quarter and a half of the populations affected.

The worst pandemic of relatively modern times was the "Spanish Flu" outbreak of 1918-19, which killed between 3 and 5 percent of the world's people. It was bad, but it hardly compares with the older plagues.

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