Brazil’s Zika outbreak may be far worse than had previously been believed, the country’s top health official claimed on February 1, because the vast majority of infected people do not show any symptoms. Zika is a mosquito-borne virus that has recently begun spreading through Latin America for the first time. Some researchers claim that it may be linked to thousands of new cases of a congenital condition called microcephaly in Brazil, although very few microcephaly cases have actually shown any trace of the virus.

Concern over the possibility that Zika infection of pregnant women may be causing microcephaly has caused the World Health Organization to declare the Latin American Zika outbreak a global emergency. Microcephaly is characterized by an abnormally small head and, often, underdeveloped brains. In 90 percent of cases, microcephaly results in hampered physical and mental development. READ MORE