Round-up is not going to cause microcephaly. I wonder what the nutritional status of women in that area is. I wonder if they are all vaccinated for rubella (a known risk factor). I wonder if some of the genetic conditions associated with microcephaly are common in that area (which is more likely if a lot of inbreeding goes on there).
Until the cases are investigated and the causes are determined, it is, indeed, early to blame Zika for it.