That belief was bolstered Friday by two studies published in medical journals.
Researchers working with lab-grown human stem cells "suspect they have discovered how the Zika virus probably causes microcephaly in fetuses," reported the journal Cell Stem Cell.
The researchers, working in the laboratory, determined the Zika virus selectively infects cells in the brain's cortex, or outer layer, making those cells "more likely to die and less likely to divide normally and make new brain cells," according to a press release from the journal.
While bolstering the connection between Zika virus and brain defects in babies, one of the researchers cautioned that it doesn't establish a conclusive link.
"While the study doesn't definitely prove that Zika virus causes microcephaly, it's very telling that the cells that form the cortex are potentially susceptible to the virus and their growth could be disrupted by the virus," said Dr. Guo-li Ming, a professor at Johns Hopkins' Institute for Cell Engineering.
These lab-grown cells might be used to screen for drugs that protect the cells, Cell Stem Cell said.
Meanwhile, the New England Journal of Medicine reported on research conducted on 88 pregnant women in Rio de Janerio, one of the nations suffering most from the Zika virus.
The scientists concluded that Zika infection during pregnancy has "grave outcomes, including fetal death, placental insufficiency, fetal growth, restriction, and [central nervous system] involvement," the journal said.
The study said blood and urine tests found 72 of the 88 women had the Zika virus.
Of the 42 infected women who had ultrasounds, major fetal abnormalities were found in 12 of them -- nearly a third.
The abnormalities included microcephaly, calcification of the brain, abnormal flow of amniotic fluid, abnormal flow of blood to the brain and fetal deaths, the study said.
"In summary, we believe that our findings provide further support for a link between maternal Zika infection and fetal and placental abnormalities that is not unlike that of other viruses that are known to cause congenital infections," the study said.
The main points of the report:
--Since January 2015, 41 countries and territories have reported Zika virus transmission.
--Thirty-one of these countries and territories are in the Americas.
--Increases in microcephaly and other neonatal malformations have been reported in Brazil and French Polynesia.
--Increases in Guillain-Barré syndrome linked to Zika have been reported in eight countries and territories.
The Zika virus is a flavivirus, part of the same family as yellow fever, West Nile, chikungunya and dengue. But unlike some of those viruses, there is no vaccine to prevent Zika or medicine to treat the infection.