Let’s talk about Zika, how much is known about this disease, what causes it, and how dangerous is it? These are some of the questions we will answer in this article! Read on to find out more!
Why did Zika travel so rapidly?
Given the episodes of the Zika outbreak in Singapore, the rate of virus transmission should really not be underestimated. Dr. Diamond, professor of molecular microbiology, and of pathology and immunology, echoes the general consensus:
“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.”
Is the eye the culprit?
Luckily, we don’t have to look far. Research carried out by the University of Washington in St Louis suggested that our eyes could be the culprit. Researchers experimented on mouse fetuses, newborns, and adults by infecting them with the Zika virus under the skin, because this parallels the way humans would be infected after being bitten by mosquitoes.
They found that live viruses were found in the eyes 7 days after the initial infection. In addition, “about a third of all babies infected in utero with Zika show eye disease such as inflammation of the optic nerve, retinal damage or blindness after birth,” whereas “in adults, Zika can cause conjunctivitis — redness and itchiness of the eyes — and, in rare cases, uveitis.”
It makes sense that the Zika virus hides in the eye, as the eye is an “immune-privileged site,” which means that they are less sensitive and will not trigger an immune response as easily as other parts of the body if an antigen invades. This is so that the eye can “avoid accidentally damaging sensitive tissues responsible for vision in the process of fighting infection.” Thus, a lot of infections actually remain in the eye even if the rest of the body has been cleared of it.
However, while we know this phenomenon of ocular immune privilege, scientists are still unsure about the travelling mechanism of the virus–did they travel in the traditional way–crossing the blood-retina barrier and then travelling along the optic nerve? Or did they travel by some other route?
Implications and future directions
But before everyone flees away from crying survivors, fearing that those very tears could be the culprit of transmission, consider this: there could be some physiological differences between mice and humans. Hence, even if this happens in mice, it might not in humans, thus, further “complementary studies in human patients infected with the virus” must be executed.
Furthermore, consider this: “researchers found that the tears of infected mice contained Zika’s RNA — the genetic material from the virus — but not infectious virus when tested 28 days after infection.” So even if human tears are infectious, it also depends on the window of time when you come into contact. Moreover, this knowledge would have implications for corneal transplantations, as it could be accidentally transmitted.
On the other hand, if human tears are not infectious, not only can we breathe a sigh of relief, but this can also prove beneficial in the long run:
Less painful way of viral RNA testing: Human tears can be used to test viral RNA, instead of drawing blood, which is a more painful option.
Pharmaceutical testing targets: Similarly, pharmaceutical companies can use human tears to test for anti-Zika drugs. Or alternatively, using mouse eyes.
Application of drugs: According to Apte, a professor of developmental biology and of medicine, there are a lot of benefits of applying drugs to the eye,
“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.”
Zika Virus and abortion
The Zika virus, temporarily associated with “clusters of microcephaly and Guillain- Barre’s Syndrome (GBS)”, was classified as a PHEIC (Public Health Emergency of International Concern) by the WHO on 1st February 2016. Yet, despite the global Strategic Response Framework launched by the WHO (including measures such as enhancing surveillance for Zika virus infection, controlling the vector–the Aedes species mosquitoes etc.), there are still ongoing infections.
You might be wondering why the Zika virus was declared as a health emergency, on par with Ebola, when the latter cause more devastating deaths with people dying of internal haemorrhages? To understand, we first need to make sense of microcephaly and GBS. You may already know that microcephaly means an abnormally small head. However, this is not merely a visual difference. With a small head, the brain becomes underdeveloped and can cause health issues such as intellectual disability, developmental delays and seizures. The Brazil Ministry of Health has also reported an increase in patients with GBS who have been infected by the Zika virus. GBS is an extremely rare autoimmune disease, whereby the body’s own immune system attacks its peripheral nervous system, demolishing the myelin sheath, which is essential for electrical insulation.
With risks of their babies contracting these neurological disorders and neonatal malformations, which would greatly decrease their standard of living, abortion requests increased by a third in affected countries – while Brazil saw a doubling of these requests. In these countries, abortion is illegal, so women resorted to the Internet to buy abortion pills (mifepristone and misoprostol), the safety of which is yet to be confirmed. However, are these desperate mothers-to-be to be blamed? Governments and the WHO are only advising women to avoid mosquito bites by using insect repellents and wearing long-sleeved clothing, which stands in stark contrast to the views of the International Planned Parent Federation who said that “contraception and abortion must be included in the fight against the Zika virus.” Which party do you agree with?
The real cause of microcephaly
When the Zika virus first broke out, a startling increase of microcephaly in infants found in Brazil raised the query of whether the two have a causal relationship. Although there was “no single piece of evidence providing conclusive proof that Zika virus infection is a cause of microcephaly and other fetal brain defects,” upon careful consideration of the existing pieces of evidence and using established scientific criteria, the Centres for Disease Prevention and Control (CDC) and the WHO confirmed the Zika-microcephaly link in April, 2016. This may appear to be a hasty act for the two international organisations to issue their confirmation instead of waiting for further supportive evidence, but, in fact, having this confirmed causal link is important for driving other preventative measures, as well as leading to more focused research. In the long term, this translates into better patient care and prevention.
The New England Journal of Medicine casts doubts on this link by comparing the confirmed microcephaly cases in two affected countries, namely Brazil and Columbia. In Brazil, the microcephaly rate “soared with more than 1500 confirmed cases,” yet, in the same duration, with nearly 12000 pregnant women with clinical symptoms of Zika infection, there were no microcephaly cases. If Zika was the real culprit, how can we explain such contrasting pieces of evidence? So, if Zika is not our enemy that has caused infants with abnormally small heads, who is?
A possible culprit was mentioned in the same journal: it was said that the pesticide pyriproxyfen, used by Brazilians to kill the larvae of the Aedes mosquitoes (the vector of Zika transmission) in drinking water is a juvenile hormone analog (ie. similar in structure and chemistry to hormones that regulate insect growth, development and reproduction). It can react with a chemical in our body (retinoic acid–a metabolite of Vitamin A) to cause microcephaly. However, in a report issued by the WHO on 29th April 2016, they claimed that a team of WHO scientists who “reviewed data on the toxicology of pyriproxyfen” found no evidence that this is the case.
It is impossible to know which party is right due to inconclusive evidence, but hopefully, with more attention diverted to these various complications, we can soon find a solution.
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