Can scientists prove Zika virus is causing birth defects?

Can scientists prove Zika virus is causing birth defects?

The cases closely followed the country's first outbreak of the tropical virus Zika, which was thought to cause no more than a mild illness that clears up in a week.

Lab tests have detected the virus in the brain tissue of a few babies with microcephaly.

Proving the cause is a bit like prosecuting a murder investigation, with Zika as the apparent killer but a lot of unanswered questions, said Dr. Ernesto Marques, a University of Pittsburgh microbiologist who is collaborating with Brazilian researchers.

[...] it's not considered ethical to infect people, especially pregnant women, in an experiment to see what happens — not when there seems to be a real chance that a volunteer could be seriously harmed.

[...] researchers are turning to other kinds of studies to try to establish whether Zika or some other factor is causing the birth defect or, also, a paralyzing condition called Guillain-Barre.

For the birth defect research, that means recruiting a group of women with babies born with microcephaly and trying to sort out what may have happened during their pregnancy to spark the condition.

The CDC was in the coastal city of Salvador last month to help health officials with another look-back study, this one targeting Guillain-Barre.

In Brazil, Zika's possible link to microcephaly emerged in September, when a spike in babies born with the condition got the attention of Dr. Vanessa van der Linden, a pediatric neurologist at a hospital in northeast Recife that works with disabled children.