RIO DE JANEIRO, Brazil (AP) — The dengue-like Zika virus has been linked for the first time to cases of babies being born with small heads, or microcephaly, Brazil’s Government said.

It said scientists studying a surge of such cases in north-eastern Brazil found the presence of the virus in the blood of a baby born with birth defects in Ceara state. The girl died.

“This is an unprecedented situation in the global scientific community,” the Health Ministry said in a statement released Saturday.

Researchers with the US Centers for Disease Control and Prevention are coming soon at the request of Brazil’s Government to study the link between the rare neurological condition and Zika.

Brazilian health officials believe pregnant women are more vulnerable of developing fetuses with microcephaly if they are infected with Zika in their first trimester. So far in 2015, the ministry has reported 739 cases of babies born with microcephaly in nine states that have been hit hard by Zika infections, while last year the same region reported only 45.

“Research on the subject should continue to clarify issues such as how it is transmitted, what it does to the body, how the fetus gets infected and the time of greatest vulnerability for pregnant women,” the ministry’s statement said.

Microcephaly “usually reflects an underlying reduction in the size of the brain”, according to the CDC. The disorder can affect motor skills and cause mental retardation.

The same mosquito that carries the dengue virus, Aedes aegypti, is also responsible for spreading Zika, a disease that until now was known as a mild version of dengue with symptoms such as fever, rash and joint pain.

Before Brazil, outbreaks of Zika have occurred in Africa, Southeast Asia and the Pacific Islands. The virus is not found in the United States, but cases of Zika have been reported in returning travellers, according to the CDC.

In its statement, the Health Ministry reported two other deaths associated with the Zika virus not involving microcephaly. The victims were an adult male who suffered from lupus and a 16-year-old girl.