The hope is that by treating babies in the womb it may be possible to prevent, or at least reduce the extent of, birth defects.
The study involved isolating strains of antibodies (infection-fighting proteins) from the blood of people who'd recovered from Zika. Scientists picked the antibodies that were most active against several strains of the virus. They then tested their effect on pregnant mice infected with Zika.
The mouse foetuses were much more likely to survive if their mothers had been given antibodies, and there was less evidence of damage to the foetus or placenta.
Results in mice cannot tell us whether the treatment will be safe or effective in humans. So the researchers say the treatment should next be tested on monkeys, as their pregnancies and reactions to Zika virus are more similar to humans.
The need for effective Zika treatments is pressing as a study from earlier this summer estimated the current epidemic would last for at least three more years.
Advice for pregnant women
Scientists believe there's enough evidence to show Zika virus infection is a cause of birth defects, including microcephaly.Pregnant women are therefore recommended to postpone non-essential travel to areas with active Zika transmission until after pregnancy.
Discuss your travel plans with your GP, practice nurse or a travel clinic. If travel is unavoidable, you should take extra care to avoid being bitten by mosquitoes.
Public Health England (PHE) provides regular updates about the current spread of the disease.
Where did the story come from?
The study was carried out by researchers from Vanderbilt University Medical Center in Nashville and Washington University School of Medicine in the US.It was funded by the US National Institutes of Health and grants from the charitable institutions Burroughs Wellcome Fund and the March of Dimes.
The study was published in the peer-reviewed journal Nature on an open-access basis so it's free to read online (PDF, 8.5Mb).
BBC News covered the main findings of the study accurately and made it clear that the treatment is not yet ready to be used in humans.
What kind of research was this?
This was experimental research carried out on mice in a laboratory.Research in mice is a common early step when scientists are developing a treatment, but it doesn't tell us whether the treatment will be safe or effective in humans.
What did the research involve?
Researchers analysed blood from three people who'd had Zika, and isolated antibodies that seemed to bind to the Zika virus and inhibit its spread. They tested the most promising antibody as a treatment for mice infected with Zika virus, and also on pregnant mice infected with the virus.They compared results for those given the antibody treatment and those given an inactive treatment.
Because mice have natural resistance to Zika virus, the researchers had to give them a treatment that suppressed their immune system and made them more vulnerable to the infection.
After treatment, researchers checked to see how long the mice survived, how many of the mouse pregnancies survived, and how much virus was found in the placenta or the mice brains.
They also tested giving the treatment before the mice were infected with Zika, on the same day, or five days after infection.
What were the basic results?
Mice treated with antibodies on the day after infection all survived for at least 20 days, while only 40% of untreated mice survived Zika infection for 20 days.Later treatment was less successful, but mice treated five days after infection were still much more likely to survive.
Almost all mouse pregnancies survived up to 13 days where the mother had been treated with antibodies a day before being infected with Zika virus, while most pregnancies of untreated mice did not survive Zika virus infection.
When the researchers looked at tissues from the mice at the end of the study, they found much higher concentrations of Zika virus in the head of the mouse foetus and the foetal placenta, in untreated mice, compared to those treated with antibodies.
Levels of the virus were also higher in the brains and blood of the mice mothers who didn't have antibody treatment.
How did the researchers interpret the results?
The researchers say they've shown that antibody therapy, either before or after exposure to Zika virus, "reduced infection in mothers, and in placental and fetal tissues." Importantly, they say that "the extent to which these observations in mice translate to humans remains unclear", and recommend further animal studies in monkeys.They say that if these results were positive, antibody treatment could be developed as a way of treating Zika infection during pregnancy.
Conclusion
For most people, Zika virus infection causes a mild flu-like illness. But it can cause serious damage to unborn children, if their mothers catch the virus while they are pregnant.At present, there's no treatment that can help protect these babies against the effect of the virus, so news that a treatment may be on the way is welcome.
However, this research is in the very early stages. Mice and humans react very differently to Zika virus, and there are important differences in the structures of mouse and human bodies during pregnancy.
This means we don't know whether this treatment would work in the same way, or if it would even be safe for humans. Much more work is needed before this is a viable human treatment.
For now, the best thing you can do is to try to avoid becoming infected in the first place – especially if you're pregnant.
Pregnant women are being advised to postpone non-essential travel to areas with active Zika virus transmission. If you travel to an affected area, you can reduce your risk of catching the virus by using insect repellent and wearing loose clothing that covers your arms and legs.
Public Health England (PHE) provides regular updates about the current spread of the disease.
Analysis by Bazian. Edited by NHS Choices. Follow NHS Choices on Twitter. Join the Healthy Evidence forum.