Washington: An antibody that protects from dengue virus is also effective against Zika, a study has found, paving the way for new drugs to prevent the infection that causes babies to be born with serious birth defects.


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Brazil and other areas hardest hit by the Zika virus are also home to dengue virus, which is spread by the same mosquito species.


Antibodies remain in the bloodstream for weeks, so one or a few doses of an antibody-based drug given over the course of a woman's pregnancy potentially could protect her foetus from Zika, with the added benefit of protecting her from both Zika and dengue disease, the researchers said.


Dengue causes high fever, severe headaches, and joint and muscle pain in children and adults but does not directly harm foetuses.


"We found that this antibody not only neutralises the dengue virus but, in mice, protects both adults and foetuses from Zika disease," said Michael S Diamond, professor at Washington University in the US.


Since dengue and Zika are related viruses, the researchers reasoned that an antibody that prevents dengue disease may do the same for Zika.


The scientists infected nonpregnant adult mice with Zika virus and then administered one of the anti-dengue antibodies one, three or five days after infection.


For comparison, another group of mice was infected with Zika virus and then given a placebo.


Within three weeks of infection, more than 80 per cent of the untreated mice had died, whereas all of the mice that received the anti-dengue antibody within three days of infection were still alive, and 40 per cent of those that received the antibody five days after infection survived.


To find out whether the antibody also could protect foetuses from infection, the researchers infected female mice on the sixth day of their pregnancies with Zika virus and then administered a dose of antibody or a placebo one or three days later.


On the 13th day of gestation, the amount of Zika's genetic material was 600,000 times lower in the placentas and 4,900 times lower in the foetal heads from the pregnant mice that were treated one day after infection, compared with mice that received the placebo.


However, administering the antibody three days after infection was less effective. It reduced the amount of viral genetic material in the foetal heads nineteenfold and in the placentas twenty-threefold.


The findings suggest that for the antibody to effectively protect foetuses from Zika infection, it must be administered soon after infection.


Such a goal may be unrealistic clinically because women rarely know when they get infected.


However, giving women the antibody as soon as they know they are pregnant could provide them with a ready-made defense against the virus should they encounter it.