When an animal is infected with Zika, the virus can spread to the eyes, and genetic material from the virus can find its way into the tears, according to a new study in mice.
The finding raises the possibility that people might contract Zika through contact with the tears of an infected person, the researchers said.
However, much more research is needed to show that such transmission is possible, the researchers said. In the new study, the researchers did not find live Zika virus in the tears of mice. Instead, they found RNA (a type of genetic material) from the virus in the animals' tears.
They also found that one week after an animal was infected with Zika, the mouse's tears could not spread the virus to other mice. But the researchers cautioned that more studies are needed to determine whether tears can spread Zika in people.
"Even though we didn't find live virus in mouse tears, that doesn't mean that it couldn't be infectious in humans," study co-author Dr. Jonathan Miner, an instructor in medicine at Washington University School of Medicine in St. Louis, said in a statement. "There could be a window of time when tears are highly infectious and people are coming in contact with it and able to spread it," Miner said. [Zika Virus News: Complete Coverage of the 2016 Outbreak]
In people, the Zika virus is known to cause symptoms in the eyes. In adults, the virus can cause conjunctivitis (pink eye), which involves inflammation of the transparent membrane that lines the inside of the eyelid and the covering of the white part of the eyeball. In rare cases, the virus can cause uveitis, or inflammation of the middle tissue layer of the eye, which can lead to pain, blurred vision and, in severe cases, blindness. Babies infected with Zika in the womb can also have damage to their eyes or blindness after birth, the researchers said.
In the new study, the researchers injected adult mice with the Zika virus. The investigators found that the virus was able to travel to the animals' eyes and infect several regions of the eye, including the iris, retina and optic nerve.
Because the body's immune system is less active inside the eye, infections of the eye can sometimes linger for long periods after they have been cleared from the rest of the body, the researchers noted. For example, in previous research, some patients infected with Ebola were found to have that virus in their eyes months after they were considered cured of the disease.
The researchers in the new study said they are planning to conduct more experiments to find out whether Zika can persist in the compartments of the eye. If Zika does linger in the eye, this could have implications for corneal transplants, because the virus might be spread from a donor to a recipient during transplantation, the researchers said. In the future, it's possible that doctors may need to test corneal tissue used for transplantation for the Zika virus, the researchers said.
The study is published today (Sept. 6) in the journal Cell Reports.
Original article on Live Science.