Zika virus infection may cause lasting eye diseases and may be thus posing a wider threat in human pregnancies than previously thought, scientists have found.
The study, conducted on rhesus monkeys, showed that although the foetus affected with Zika virus did not show its typical symptoms such as shrunken heads or microcephaly, unusual inflammation in the foetal eyes, in the retinas and optic nerves, in pregnancies infected were observed.
"Our eyes are basically part of our central nervous system. The optic nerve grows right out from the foetal brain during pregnancy," said Kathleen Antony, professor at the University of Wisconsin-Madison.
"It makes some sense to see this damage in the monkeys and in human pregnancy -- problems such as chorioretinal atrophy or microphthalmia in which the whole eye or parts of the eye just don't grow to the expected size," she added.
In the study, published in the journal PLOS Pathogens, the team infected four pregnant rhesus macaque monkeys with a Zika virus dose similar to what would be transferred by a mosquito bite.
The findings revealed that the virus was present in each monkey's foetus.
"That is a very high level -- 100 per cent exposure -- of the virus to the foetus along with inflammation and tissue injury in an animal model that mirrors the infection in human pregnancies quite closely," Golos said.
Moreover, three of the foetuses involved had small heads, but not quite so small as children born with microcephaly.
Studying Zika infection in monkeys may help follow the progress of the mosquito-transmitted infection and associated health problems in humans, the researchers said.
"The results we're seeing in monkey pregnancies make us think that, as they grow, more human babies might develop Zika-related disease pathology than is currently appreciated," Golos noted.
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