Larvicide Manufactured By Sumitomo, Not Zika Virus, True Cause Of Brazil's Microcephaly Outbreak! Pregnant women all over the world have been advised to take caution. The Zika virus infection has been linked to newborn babies with the birth defect microcephaly. This is a congenital condition in which babies are born with unusually tiny heads. The notion, however, has recently been challenged by a group of Argentine physicians. The group suspects that the Zika virus is not to blame for the rise in microcephaly cases, but that a toxic larvicide introduced into Brazil's water supplies may be the real culprit.