<p>The explosive spread of the Zika virus, and the fear that it might be causing birth defects, is now the World Health Organization&#39;s fourth-ever international public health emergency.&nbsp;</p><p>The decision comes after outbreaks in South America were linked to a rise in microcephaly, a condition that can mean babies&#39; brains don&#39;t develop normally. The fear is that the virus is causing the condition, most likely when infected mosquitoes bite pregnant women, but that&#39;s still not conclusive.&nbsp;</p><p>The WHO isn&#39;t waiting around for a final verdict. It&#39;s been criticized for taking too long to declare 2014&#39;s Ebola outbreak an international public health emergency.&nbsp;<a href="https://www.youtube.com/watch?v=pMKUPh0ZCKQ" target="_blank">Director-General Margaret Chan</a>&nbsp;has said she doesn&#39;t want people&nbsp;<a href="http://www.nytimes.com/2016/02/02/health/zika-virus-world-health-organization.html" target="_blank">to say it failed</a>&nbsp;to take action this time.&nbsp;</p><p>Declaring something an emergency can be a big deal: The organization&#39;s decision can kick-start new research into fighting diseases and lead to travel and trade restrictions.</p><p>At this point, the WHO says the Zika virus doesn&#39;t merit those kinds of restrictions. For now, most of its efforts will go into mosquito control.&nbsp;</p><p><i>This video includes images from Getty Images.&nbsp;</i></p>