Zika Virus Can Live in Your Eyes

As research into the Zika virus rapidly advances, we’re learning there are a number of ways the virus may spread — possibly even through our tears. How so, you say? Researchers from Washington University School of Medicine in St. Louis this week released study results showing the Zika virus can live in our eyes.

Published Sept. 6 in Cell Reports, the study describes the effect of the Zika virus infection in the eyes of mouse fetuses, newborns, and adults. This may explain why some Zika patients develop eye disease, including a condition known as uveitis — which can lead to permanent vision loss.

Related: The Zika Zeitgeist: What You Must Know

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

Zika can cause anything from mild disease to debilitating conditions in adults, and it can cause brain damage and death in fetuses. About a third of all babies infected in utero with Zika show eye disease such as inflammation of the optic nerve, retinal damage, or blindness after birth.

In adults, Zika can cause conjunctivitis — including redness and itchiness of the eyes — and, in rare cases, uveitis. Complementary studies are now planned in patients infected with the virus.

Researchers want to learn whether the virus typically infects the eye by crossing the blood-retina barrier that separates the eye from the bloodstream, traveling along the optic nerve connecting the brain and the eye — or through some other route.

Researchers are considering alternative routes of transmission, as the virus is spreading more quickly than expected.

“There could be a window of time when tears are highly infectious and people are coming in contact with it,” Jonathan J. Miner, M.D., Ph.D., an instructor in medicine and the study’s lead author, said in a statement.

The eye is an immune privileged site — the immune system is less active there to avoid accidentally damaging sensitive tissues responsible for vision in the process of fighting infection. So infections sometimes persist in the eye after they have been cleared from the rest of the body.

Zika researchers are increasingly considering alternative routes of transmission because the virus is spreading more quickly than expected by mosquito-borne transmission alone.

Epidemiologists can predict the spread of a disease based on known rates of transmission for related viruses and the viral level in the bloodstreams of infected people. By those calculations, Zika, they say, is moving unusually fast.

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Even if human tears do not turn out to be infectious, the researchers say the detection of live virus in the eye and viral RNA in tears still has benefits. Human tears potentially could be tested for viral RNA or antibodies — as a less painful way to diagnose Zika infection than drawing blood.