A link between a form of fetal brain damage and the mosquito-born zica virus has been confirmed by Brazilian health authorities on Saturday.
The link between zica, first medically identified as a new disease half a century ago, and birth defects has never been made.
The virus, endemic in parts Africa, South America, Southeast Asia and some Pacific Islands, has until now been blamed for symptoms such as fever, mild headache, skin rashes, joint pain and conjunctivitis, or "red eye."
Initial analysis shows that the virus can be passed to a fetus and that the fetus is at greatest risk from the virus during the first three months of pregnancy, the statements said.
More tests and studies are needed to clarify the exact method of transmission and infection, the statement added.
A surge in recent months of babies born with microcephaly, or an unnaturally small brain, in Brazil's northeast, led authorities to suspect the virus may have more sinister effects than previously recorded, the ministry said.
Microcephalic children can suffer developmental and intellectual difficulties that limit intelligence and muscle coordination for life.
The ministry's conclusion was made after tests on the tissue of a deceased child with microcephalic symptoms by the Ivandro Chagas Institute in Belem, Brazil, one of South America's leading health institutes. There is also evidence that zica has contributed to the deaths of adults weakened by other diseases.
Zica is transmitted by the Aedes aegypti mosquito also known to carry the yellow fever, dengue, chikungunya viruses.
The ministry said that the new information means that zica has become a serious risk to public health and that Brazil must embark on an emergency program to control the Aedes aegypti mosquito to prevent the virus' spread.
Brazil has invited the Atlanta, Georgia-based US Center for Disease Control to visit the country and observe research and control efforts, the health ministry said.