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Foetal brain damage worse if Zika-infected mothers previously had dengue

SINGAPORE — A mother with immunity to dengue, but who has the Zika virus, could give birth to a child with more severe brain damage, researchers who experimented on mice have found.

The researchers found that Zika infection in mothers with dengue antibodies resulted in foetuses with much smaller body mass and head circumference, as well as more significant damage to brain tissue.

The researchers found that Zika infection in mothers with dengue antibodies resulted in foetuses with much smaller body mass and head circumference, as well as more significant damage to brain tissue.

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SINGAPORE — A mother with immunity to dengue, but who has the Zika virus, could give birth to a child with more severe brain damage, researchers who experimented on mice have found.

The researchers from Duke-NUS Medical School and their colleagues wanted to find out why some — but not all — Zika infections during pregnancy led to brain abnormalities in foetuses.

They also wanted to know if the severity of a foetal infection had anything to do with a mother’s previous dengue infection.

Both the dengue and Zika viruses are typically spread by the Aedes mosquito. But Zika can be transmitted from infected mothers to their foetuses. While Zika infection is generally mild, it caused panic a few years ago when linked to an increase in cases of infants born in Brazil with smaller head circumferences than normal, or microcephaly.

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INTERACTION BETWEEN DENGUE AND ZIKA VIRUSES

The researchers found a surprising interaction between the dengue and Zika viruses.

When a mother who has dengue antibodies is infected with Zika, the dengue antibodies attach to the Zika virus, forming a structure called an “immune complex”.

A receptor on the mother’s placental cells recognises the immune complex and allows the Zika virus to travel across the placenta into the foetal cells.

The researchers found that Zika infection in mothers with dengue antibodies resulted in foetuses with much smaller body mass and head circumference, as well as more significant damage to brain tissue.

When the receptor on the placental cells was blocked, the Zika transmission from mother to foetus was reduced, resulting in larger head circumference and less brain damage.

More research is needed to determine if previous dengue infection has the same effect on human babies born to women infected with Zika during pregnancy, researchers said.

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BETTER TREATMENT OPTIONS?

Assistant Professor Ashley St John, one of the authors of the study, said: “Our research indicates that previous immunity of the mother to dengue could be a risk factor for severe outcomes in infants born to mothers infected with Zika virus during pregnancy.

"This is highly significant, since current Zika virus epidemic regions overlap to a large extent with those of dengue viruses, and this work informs our understanding of mechanisms that could influence the severity of infection with Zika virus.”

The novel mechanism that leads to a Zika virus transfer from mother to foetus could also be relevant in other viral infections that can be transmitted from mother to foetus, such as the human immunodeficiency virus (HIV) and cytomegalovirus, said Asst Prof St John, who is from the Duke-NUS’ Emerging Infectious Diseases programme.

The research team aims to use its findings to develop better treatment options for Zika virus infection during pregnancy.

DENGUE INFECTIONS CAN REDUCE ODDS OF GETTING ZIKA

The findings by Duke-NUS researchers builds on a study reported last month by United States and Brazilian researchers, which found that prior infection with dengue could reduce the risk of contracting Zika by nearly half.

The study was based on tests of blood samples of nearly 1,500 women in Salvador, Brazil, which was hit hard by the Zika epidemic in 2015.

It found that the high infection rate of the Zika virus — 73 per cent of the study participants — explains the high numbers of infants later born with microcephaly.

The study also found that women who had been previously exposed to dengue were almost 50 per cent less likely to be infected by Zika.

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