Zika virus can live in tears, study finds
The zika virus can live in the eyes with tears, spreading the mosquito-borne disease further, new research suggests.
Washington University School of Medicine in St Louis, United States, are trying to find out if Zika is being transmitted from person to person in ways other than mosquito bites because the virus is spreading more quickly than would be expected.
Senior author Professor Dr Michael Diamond said: "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. Sexual transmission is probably not playing a major role, but it could be some other body fluids - saliva, or urine or tears.
"Our study suggests that the eye could be a reservoir for Zika virus. We need to consider whether people with Zika have infectious virus in their eyes and how long it actually persists."
The new study, published in Cell Reports, was carried out on mice to work out what effect Zika infection has on the eye.
Researchers infected adult mice under the skin - similar to the way humans are infected by mosquitoes - and found live virus in the eyes seven days later.
The tears of Zika-infected mice contained the virus RNA - the genetic material from the virus - but their tears were not infectious 28 days after initial infection.
Lead author Dr Jonathan Miner said: "Even though we didn't find live virus in mouse tears, 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."
The immune system is less active in the eyes, so infections sometimes live on there even after they have been cleared from the rest of the body.
The good news is that top scientists think even if human tears do not turn out to be infectious, their detection of live virus in the eye and viral RNA in tears will have practical benefits.
Human tears could be used to test whether or not someone is infected with Zika, which is a lot less painful diagnosis method than a blood test, and mouse eyes could be used to test anti-Zika drugs.
Professor Dr Rajendra Apte, the study's other senior author, explained: "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.
"And 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."
The study findings also help to explain why around a third of all babies born with Zika have eye disease. They are often born completely blind, or have an inflamed optic nerve or damaged retina.