(CN) - Genetic material from the Zika virus has been found in the tears of mice, adding another dimension to the threat posed by the mosquito-borne virus.
In a study published Sept. 6 in the journal Cell Reports, a team of researchers from Washington University School of Medicine in St. Louis presented the results of tests on the eyes of adult, newborn and fetus mice.
The findings help explain why some Zika patients develop uveitis, a condition that can lead to permanent vision loss.
"Our study suggests that the eye could be a reservoir for Zika virus," said study co-author Michael Diamond. "We need to consider whether people with Zika have infectious virus in their eyes and how long it actually persists."
While Zika typically causes mild symptoms in adults or no tangible effects in about 20 percent of cases, a growing body of research highlights the virus's connection to a series of health conditions, including Guillain-Barre syndrome - an autoimmune disorder that causes the body to attack parts of the peripheral nervous system.
Zika presents additional risk for pregnant women, as the virus has been connected to microcephaly, which results in a baby having an abnormally small head and potential brain damage. Microcephaly has also been connected with miscarriages and stillbirths.
In the study, the team infected adult mice under the skin to mimic a mosquito bite, and found that Zika can live in the eye for seven days. This seems to confirm that the virus is able to travel to the eye, though the route it takes is still not confirmed.
Eye infections suggest that people may be able to acquire the virus through contact with tears from infected people. The team found that the mice's tears contained Zika's RNA - the genetic material from the virus - when tested 28 days after infection, though the virus was no longer infectious.
"We are planning studies in people to find out whether infectious virus persists in the cornea or other compartments of the eye, because that would have implications for corneal transplantation," study co-author Rajendra Apte said.
Other blood-borne viruses like herpes have been transmitted accidentally through corneal transplants.
Researchers are considering alternative methods of transmission since the virus is spreading more rapidly than would be expected by mosquito bites and sexual activity - the only known methods of transmission.
"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," Diamond said. "Sexual transmission is probably not playing a major role, but it could be some other bodily fluid - saliva, or urine or tears."
Even if human tears turn out to not be infectious, analyzing tears could still offer a less painful method of testing for viral RNA or antibodies.