Zika Was First Discovered in 1947. Why Is it Now a Threat?

Mostly innocuous and fairly unknown until a few weeks ago, the Zika virus is suddenly dominating the news. Under scrutiny is the virus’s putative link with a congenital birth defect called microcephaly, which causes babies to be born with abnormally small heads and undeveloped brains.

Two recent publications [1,2] have documented finding the genome of the Zika virus in the amniotic fluid and brains of fetuses affected by microcephaly from three different mothers. These numbers are still too small to constitute a proof, and in fact, alternative theories are already cropping up: an organization of Argentinean doctors has published a report in which they claim that it’s not the virus, rather the insecticide used against the mosquitos, that causes the birth defect.

But what is Zika and, if the claims about microcephaly turn out to be true, how can it be harmless to most people yet so detrimental to a developing fetus? To answer these questions we have to take a step back and understand how viruses work and why some are endemic in the population, while others seem to come and go in waves.

The Zika virus was first isolated in 1947 from a rhesus monkey and from a pool of mosquitos in the Zika forest in Uganda. It belongs to the same family of viruses as dengue, yellow fever, and West Nile virus. However, unlike its close relatives, Zika was thought to be relatively harmless: most infected people experience no symptoms and a few have just a rash and mild fever. Originally confined to Africa, Zika started expanding to Asia in 2007. Since then the virus has spread exponentially.

Viruses like Zika are similar to Ebola in that they replicate in animal populations, where they are endemic. Ebola, for example, usually infects bats and —> Read More

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