Experts from Washington University and Colorado State University have recently found traces of Zika virus genome in the tears of mice infected with the virus. Crucial in its finding, the study signals towards a possible virus transmission by coming in contact with the infected tears.
The study also solves the mystery surrounding eye diseases that develop in the wake of Zika infection. These virus-caused eye infections can be so severe that they can even lead to permanent loss of vision.
Published in the online journal Cell Reports on 6th September, this study carries diagnosis and therapeutic development implications to fight off Zika virus.
Originating from Brazil in 2015, the virus disrupts brain development in fetuses and causes microcephaly in infants born to virus infected mothers. Zika is now being extensively studied globally by epidemiologists and medical experts.
Despite the tireless research, the virus continues to affect quality of life for many people, prompting actions to contain population of the carrier mosquitoes in many areas.
However, till date, there is no cure for the virus which is a prime driving force for the researchers to study the virus from every possible perspective. With this finding, many unquestioned queries about the spread of the virus and detrimental effects on the health are likely to be answered.
Co-author of the study, Michael S Diamond, MD, PhD, said, “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.”
Previously documented work about Zika virus suggests that about 10% to 15% Zika infected adults suffer from an eye disease named as conjunctivitis which causes redness and itchiness in the eye due to the infection or inflammation of conjunctiva, a transparent membrane covering the eye ball.
Studies have also recorded the occurrence of uveitis in the patients, but the likelihood remains rather low. Uveitis is an eye inflammation of the middle pigmented layer of the eye tissues which leads to pain, eye redness and blurred vision, which upon getting serious can cause blindness.
In addition to this, the study also identified that newborns infected with the virus show optic neuritis bilateral iris colobomas, intraretinal hemorrhages, lens subluxation and blindness which affects over a third of infected infants. With this finding, it is hoped that these eye diseases will be minimized in children who already have a vulnerable immunity to counteract the disease effects.
These eye infections are often recorded in the patients several weeks after the initial infection which is believed to have a cause associated with a weaker immune response of the eye.
The researchers are still not certain of the route Zika virus takes to get to the eye and cause the related damage. However, they have postulated the possibilities which will be investigated further to reach a precise and reliable finding.
To closely monitor the spread of Zika virus from the bloodstream to the eye, the experts injected mice subjected with the virus. The viral titers were measured in the brain, eyes, spleen and other organs for a period of 28 days after inoculation.
On day 7, the viral RNA (genetic information) was found in the tear fluid which was equivalent to 3 x 102 focus-forming units per mL of sample. On the 28th day of the experiment, the traces of viral RNA were still present in the sample but they were lower than the threshold required for it to become infectious.
However, with the presence of the viral traces long after its clearance from the serum, the potential of spreading of virus through coming in contact with the infected tears cannot be ruled out, even if at this point these viral traces lack the ability to be infectious.
How Does Zika Virus Reach Eyes And Lead To Eye Diseases?
As mentioned earlier, nothing can be certainly said at the moment about the transfer of virus to the eyes as scientists are further investigating the routes and molecular pathways involved. It is believed that inflammatory cell recruitment might be a contributing factor in this regard.
It was also said that the direct infection of the eye might trigger inflammation as a result of virus-induced cell death, leukocyte recruitment and cytokine production.
Alternatively, another possibility looks at the pathogen-associated molecular pattern (PAMP) which in turn activates inflammatory responses which continue to cause the damage in the eye tissues in the absence of infectious virus.
The researchers went on to investigate as to how the virus crosses the blood-retina barrier to reach the eye. It was speculated that the viral particles travel along the optic nerve which connects the eye with the brain passing through the blood-retina barrier.
However, these are just intelligent guesses so far and the precise route of travel is still unknown.
This finding will lead the researchers to reevaluate the mode of transmission of the virus. Previously, the spread of sexual transmission of Zika virus has been a prime focus of disease transmission prevention, but now other bodily fluids like saliva, urine and tears are also required to be analyzed.
While a lot is still to be investigated, this study will lead the researchers in the right direction in diagnosing and treating Zika virus infected patients. While testing eye fluids will enable scientists and doctors to diagnose patients through a non-invasive procedure, the treatments for the virus in the future may also find a more targeted approach.