Into Which Category of Emergent Diseases Would Zika Virus Be

Into which category of emergent diseases would Zika virus be placed?

A) Category 1: invasion of a new host population by a known pathogen
B) Category 2: appearance of a completely new, previously unknown pathogen
C) Category 3: association of a well-known disease with a new pathogen
D) Category 4: increased virulence, or a renewed problem, with a well-known but previously less virulent or well-controlled pathogen