WASHINGTON: A new study has found genetic fragments of Zika in the eyes and the tears of laboratory mice infected with the virus, a finding that offers a potential new route of human infection.
“Our study suggests that the eye could be a reservoir for Zika virus,” said Dr. Michael Diamond of Washington University St. Louis, whose paper was published in the journal Cell Reports.
“We need to consider whether people with Zika have infectious virus in their eyes and how long it actually persists.”
For the study, the team infected adult mice under the skin, resembling the way people get infected by mosquito bites, and found live virus in the eyes a week later. When tested 28 days later, the tears of infected mice contained genetic material from the virus, but not infectious virus.
The researchers said their findings raise the possibility that Zika could be spread through contact with the tears of infected people, but said that would have to be proven.
“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 Dr. Rajendra Apte, a senior author of the study. Other blood-borne viruses such as herpes simplex virus have been transmitted accidentally through corneal transplants.
Although principally spread by mosquitoes, Zika has been shown to persist in sites of the body where the immune system is less active, including semen, vaginal fluid, saliva and now, possibly, tears.
That could help account for why Zika has spread so quickly, outpacing what might be expected if the virus were only carried by mosquitoes, Diamond said. “Sexual transmission is probably not playing a major role, but it could be some other bodily fluid – saliva, or urine or tears,” he said.
Zika infections in pregnant women have been shown to cause microcephaly – a severe birth defect in which the head and brain are undersized – as well as other brain abnormalities. The connection between Zika and microcephaly first came to light last fall in Brazil, which has since confirmed more than 1,800 cases of microcephaly.
In adults, Zika infections have also been linked to a rare neurological syndrome known as Guillain-Barre, as well as other neurological disorders.
Adult female mosquitoes can pass the Zika virus along to their offspring, U.S. researchers said on Monday, a finding that makes clear the need for pesticide programs that kill both adult mosquitoes and their eggs.
The findings, published in the American Journal of Tropical Medicine and Hygiene, show that as with many related viruses, including dengue and yellow fever, Zika can be transmitted from female mosquitoes to their offspring.
Dr. Robert Tesh of the University of Texas Medical Branch in Galveston, Texas, a study co-author, said the fact that the virus can be passed along to mosquito offspring makes Zika harder to control.
“Spraying affects adults, but it does not usually kill the immature forms – the eggs and larvae. Spraying will reduce transmission, but it may not eliminate the virus,” he said.
Although Zika generally causes mild disease in adults, it is a major threat to pregnant women because it has been shown to cause the severe birth defect known as microcephaly and other brain abnormalities.
The ongoing Zika outbreak was first detected last year in Brazil, where it has been linked to more than 1,800 cases of microcephaly, and has since spread rapidly through the Americas.
Aedes aegypti, the mosquitoes that carry Zika, lay eggs in small containers of water. Homeowners have been advised to dump out containers of water on their properties. When the water is dumped, the eggs cling in a ring around the water line, where they remain dormant until the next rain, when they can hatch.
Scientists studying Zika wanted to find out whether some of the offspring from these tropical mosquitoes might carry the virus, helping to perpetuate an outbreak during dry seasons.
To find out, researchers injected female Aedes aegypti mosquitoes raised in a laboratory with Zika. They were then fed, and within a week, they laid eggs. The team collected and cared for the eggs until they hatched into adult mosquitoes, and counted the ones that carried the Zika virus.
They found the virus present in one out of every 290 mosquitoes tested.
“The ratio may sound low,” Tesh said, “but when you consider the number of Aedes aegypti in a tropical urban community, it is likely high enough to allow some virus to persist, even when infected adult mosquitoes are killed.”
Tesh said the next step is to show that mosquitoes are actually passing Zika to their offspring in the wild.
Experts fighting Zika in the Wynwood neighborhood of Miami have announced aerial spraying campaigns using pesticides that kill both adult mosquitoes and mosquito larvae.
For homeowners in affected areas, Tesh advised people to dump standing water from containers on their property and scrub them thoroughly to remove eggs and larvae. They should also remove any objects from their yards that could collect water.