A new study from Washington University School of Medicine in St. Louis suggests that the Zika virus can live in tears. Researchers investigated the effects of the Zika virus on the eyes of mouse fetuses, newborns, and adults.
It helps explain why approximately one third of all infants infected with the virus in utero exhibit inflammation of the optic nerve, rendering them blind. In adults, Zika can cause conjunctivitis-or pinkeye- and recently, the New England Journal of Medicine reported an association with uveitis, which can cause permanent blindness. Researchers are planning to replicate studies in patients infected with the virus.
“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,” said Rajendra S. Apte, one of the researchers.
“Our study suggests that the eye could be a reservoir for Zika virus,” said Michael S. Diamond a senior author of the article. “We need to consider whether people with Zika have infectious virus in their eyes and how long it actually persists.”
Researchers injected the virus into adult mice under the skin- modeling human exposure to the virus by mosquitoes. Seven days post-infection, researchers found the live virus in the tears of infected mice. By day twenty-eight, the infectious virus was cleared, but there were detectable levels of Zika RNA. This discovery raises the possibility that Zika can be transmitted through contact with infected tears.
“Even though we didn’t find live virus in mouse tears (by day twenty-eight), that doesn’t mean that it couldn’t be infectious in humans. 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,” said Jonathan J. Miner, lead investigator for the study.
Researchers are investigating alternative routes of Zika transmissions. According to Diamond, the speed of Zika infections cannot be fully accounted by mosquito-borne transmissions and the viral load in human blood. “Sexual transmission is probably not playing a major role, but it could be some other bodily fluid – saliva, or urine or tears,” said Diamond.
Although human tears may not transmit the Zika virus, detection of the live virus and the viral RNA has practical applications. Clinicians could diagnose patients by testing for viral RNA or antibodies in human tears, which is less painful than drawing blood.
“The advantage to using the eye is that your dosing requirements are very small and you don’t have to worry as much about effects of larger dosages of therapeutic agents on the rest of the body, such as liver toxicity. If you know you have virus replicating in the eye, you can just give the drug locally and measure any change in viral replication. If you use the eye as a model to study drug delivery or drug efficacy, you could then use the knowledge you gain to treat viral infection in other places,” said Apte.