PhotoMuch of the coverage on the Zika virus has rightly focused on the devastating impact it can have for pregnant women.

Otherwise, the virus has not been classified as especially harmful to others, and symptoms tend to be so mild they are sometimes not noticed. However, some who get the virus suffer from red eyes, and even pain behind the eyes.

Researchers now think they know why. The virus, they say, can live in tears.

A study at Washington University School of Medicine in St. Louis has found that the virus can live in the eyes, and have found traces of Zika genetic material in tear drops. The scientists say their findings help explain why some people who develop the Zika virus also suffer from uveitis, a condition that potentially threatens eyesight.

A reservoir for the virus

“Our study suggests that the eye could be a reservoir for Zika virus,” said Dr. Michael Diamond, one of the study’s senior authors. “We need to consider whether people with Zika have infectious virus in their eyes and how long it actually persists.”

As has been widely reported, pregnant women who get the Zika virus stand a good chance of giving birth to babies with a condition known as microcephaly, in which the brain does not fully develop. Research also shows that about a third of the babies infected in the womb also suffer from eye disease, such as inflammation of the optic nerve.

Adults infected with the Zika virus may get conjunctivitis, a redness and itchiness of the eyes. In a few cases they may develop uveitis, though those cases are said to be rare.

In experiments on mice, the Washington University researchers found that the Zika virus can infect the eyes within about seven days. The route it takes to get there has not been determined.

A source of contagion?

While it has already been established that the Zika virus can been transmitted through sexual contact, the researchers say their study suggests it can also be transmitted through contact with tears from an infected person.

“Even though we didn’t find live virus in mouse tears, that doesn’t mean that it couldn’t be infectious in humans,” said lead author Dr. Jonathan J. Miner.

If it could, it might explain why the virus is spreading as fast as it is. Zika researchers are increasingly looking for other sources because the virus is spreading faster than expected if mosquitoes were the only source.

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