Definition: In this task, you will be presented with a passage and have to answer a question based on your understanding of the events inferred from the passage. Try to find the best answer that is most likely to fill in "_". Note that the URLs in the text have been replaced with [Link].
Input: Recife, Brazil (CNN) When Rafaela Oliveira dos Santos, 20, gave birth to her second child last October, she never imagined the challenges to come. Her baby, Luiz Felipe, was born with microcephaly, a rare neurological disorder with long-term physical and mental repercussions that has been linked to the mosquito-borne Zika virus that is spreading throughout the Americas. "At first, I wasn't concerned because the doctor where I delivered didn't tell me there was anything wrong," Santos said, as she cradled her baby in her arms. "It wasn't until I turned on the television that day that I first heard of Zika."There have been more than 4,000 cases of a birth defect linked to the mosquito-borne Zika virusThe Brazilian state of Pernambuco has been the hardest hit, registering 33% of recent cases 
 Question:The _ virus was first detected in Brazil last April.

Zika