The ironically poetic findings come as researchers are trying to understand why the virus is spreading at such an unusually quick rate.
A new study from the Washington University School of Medicine in St. Louis has discovered that Zika virus can live in eyes and the researchers have found genetic material from the virus in tears.
The work has come about as Zika researchers are confounded by the rate at which the virus is spreading, which appears to be more quickly than by mosquito-borne transmission alone. Epidemiologists say that compared to related viruses, Zika is moving unusually fast.
"The Zika epidemic has been very explosive, more explosive than we can account for by just mosquitoes and the level of Zika virus in human blood. Some other factor may be at play," says Michael S. Diamond, MD, PhD, one of the study's senior authors. "Sexual transmission is probably not playing a major role, but it could be some other bodily fluid – saliva, or urine or tears."
The research could shine light on why some people with Zika contract eye diseases like conjunctivitis, and uveitis which can lead to permanent vision loss. Meanwhile, some 30 percent of all babies infected in utero with Zika show eye conditions such as inflammation of the optic nerve, retinal damage or blindness after birth.
"Our study suggests that the eye could be a reservoir for Zika virus," says Diamond. "We need to consider whether people with Zika have infectious virus in their eyes and how long it actually persists."
In the lab the researchers found live virus in the eyes after seven days, though they were unable to confirm the method by which the virus traveled there; perhaps by crossing the blood-retina barrier that separates the eye from the bloodstream or along the optic nerve that connects the brain and the eye, or maybe another way altogether.
The new study involved testing the tears of adult mice – similar studies are being planned for human patients. Even if the sad salty tears of humans turn out not to be infectious, the researchers' detection of live virus in the eye and viral RNA in tears still has practical benefits. Among other things, human tears potentially could be tested for viral RNA or antibodies, which would offer a less painful way to diagnose Zika infection than drawing blood. The findings could have implications for eye banks as well.