BRASILIA: The cases of babies born with unusually small heads continue to rise in Brazil where researchers said they had found new evidence linking the increase to the Zika virus spreading through the Americas.

The Ministry of Health said the number suspected cases of microcephaly, a neurological disorder in which infants are born with smaller craniums and brains, increased to 3,893 by Jan. 16 from 3,530 cases 10 days earlier.

The number of reported deaths of deformed babies rose to 49, ministry officials said at a news conference.

So far, health authorities have only confirmed six cases of microcephaly where the infant was infected with the mosquito-born Zika virus.

The surge of cases since the new virus was first detected last year in Brazil led the ministry to link it to the fetal deformations and warn pregnant women to use insect repellent to avoid mosquito bites.

On Tuesday, Brazilian researchers took another step toward proving Zika causes microcephaly. The Fiocruz biomedical center in Curitiba announced it had found Zika in the placenta of a woman who had a miscarriage, proving the virus can reach the fetus.

Until now, researchers had only found Zika in the amniotic fluid of two pregnant women.

“This is a significant advance, but we still cannot scientifically state that Zika is the cause of microcephaly,” said Jean Peron, an immunology expert who is experimenting on pregnant mice at the University of Sao Paulo’s Institute of Biomedical Sciences.