The Zika virus has been circulating in South-east Asia since the 1960s, but doctors never noticed a link between the virus and newborns with abnormally small heads until recently.
This problem came to light only in October last year, when Brazil - which had been struggling with an ongoing outbreak of the mosquito- borne disease - began to notice an odd increase in the number of babies born with microcephaly.
As reported cases of the birth defect continued to climb, the country declared a national public health emergency.
Scientific evidence showing that Zika could be a cause of microcephaly slowly began to emerge. In tests by the United States Centres for Disease Control and Prevention, the virus was found in four microcephaly cases from Brazil.
The mothers of these four babies - none of whom survived past 24 hours - all had fever and rashes at some point in their pregnancies.
By Jan 21, Brazil had reported 3,893 suspected cases of microcephaly, including 49 deaths. Previously, the country had seen fewer than 200 such cases in a year.
In February, the World Health Organisation (WHO) declared the link between Zika and clusters of microcephaly and other neurological problems - such as Guillain-Barre syndrome - a public health emergency of international concern.
Research into the virus and exactly how it affects the human body is still ongoing.
Although several reports have claimed that the insecticide pyriproxyfen, rather than Zika, could be the cause of microcephaly, a team of 12 WHO experts has found no evidence that this is so.
According to the WHO, the best protection from the Zika virus is to prevent mosquito bites.