Study in mice shows Zika also attacks adult brain cells
- U.S. researchers have found that Zika can attack special populations of brain cells in adult mice in the part of the brain involved in learning and memory, raising new questions about how the virus may be impacting millions of adults who have been infected with the virus.
- Zika has already been shown to attack fetal brain cells known as neural progenitor cells – a type of stem cell that gives rise to various kinds of brain cells. The death of these cells is what disrupts brain development and leads to the severe birth defects seen in babies whose mothers were infected with Zika during pregnancy.
- U.S. health officials have concluded that Zika infections in pregnant women can cause microcephaly, a birth defect marked by small head size that can lead to severe developmental problems in babies.
- Several teams have published papers showing that in some patients, Zika can cause serious brain and spinal cord infections – including encephalitis, meningitis and myelitis – in people exposed to Zika.
- In rare cases, Zika has also been linked with Guillain-Barre Syndrome, a post-infectious autoimmune disorder that can cause temporary paralysis in adults.
About Zika Virus
- Zika virus was first isolated in 1947, in a rhesus monkey at Uganda’s Zika Forest.
- Zika is spread mostly by the bite of an infected Aedes species mosquito (Ae. aegypti and Ae. albopictus). These mosquitoes are aggressive daytime biters. They can also bite at night
- There is no vaccine or medicine for Zika.
The WHO’s prevention advice is to remove mosquito breeding sites and reduce contact between mosquitoes and people by:
- using insect repellent;
- wearing clothes (preferably light-coloured) that cover as much of the body as possible;
- using physical barriers such as screens, closed doors and windows; and
- sleeping under mosquito nets
IMA sounds Zika alert
The IMA, which is the largest association of allopathic doctors, has asked physicians and the people to be aware and vigilant. The association also said that local mosquito transmission of Zika virus infection has been reported in Singapore. Local mosquito transmission implies that mosquitoes in the area are infected with the Zika virus and are spreading it to humans.
A mystery no more
Zika is not new; the virus was first isolated in Africa in 1947. Since then, an outbreak of the mosquito-borne virus that began in early 2015 in Brazil has spread to more than 60 countries in the Americas, Africa, Asia and the Pacific islands.
A study published on September 1st in the Lancet estimates that 2.6 billion people live in areas to which Zika could eventually spread.
Start with transmission
- The vast majority of Zika infections occur through the bite of Aedes aegypti, a mosquito common in tropical climates and especially in cities.
- Another species, albopictus, which thrives in cooler climes, may also be able to transmit the bug, though possibly not as efficiently.
- Zika can also be transmitted sexually (the first case of transmission in the United States occurred this way).
- Studies are under way to find out how long after infection that remains possible, but traces of the virus’s genetic code have been found in semen six months after the onset of symptoms.
- Infection through blood transfusion has been confirmed.
- The virus has also turned up in urine, tears and saliva, though that does not necessarily mean that it can spread through them.
- Infection is also dangerous if it occurs during pregnancy: in perhaps 1-2% of cases the virus attacks the brain tissue of the fetus. That causes microcephaly, a condition characterised by an abnormally small head, a result of the skull collapsing around the shrunken brain.
Occasionally, infected people develop Guillain-Barré syndrome, a condition in which the immune system goes awry, causing weakened muscles and temporary paralysis. Death is rare, but some sufferers spend weeks hooked to a breathing machine.
Question of tracking and diagnosis
- A common test works by testing for antibodies, specialised proteins produced by the immune system that are designed to disable the virus. But it cannot distinguish easily between antibodies for Zika and those for dengue fever
An ounce of prevention
- The World Health Organisation prescribes condoms or sexual abstinence for at least six months for those returning from areas where Zika is spreading. Several countries have begun screening blood donors.
- The most encouraging news is on the vaccine front. Several are in early-stage trials. Two—one developed by the National Institutes of Health in America, and the other by Inovio Pharmaceuticals, a private firm—use a new technology called “DNA vaccination”.
About DNA Vaccines
- DNA vaccines introduce snippets of the viral genome into the patient’s cells, relying on the cells themselves to produce viral proteins that are then recognised by the immune system. DNA is much easier to handle than weakened or dead viruses; and by focusing on genetic sequences common to different variants, a vaccine may offer protection against several strains of the virus. If all goes well, large-scale trials could begin early next year, with results by mid-2018.
So the hunt is on for other ways to limit mosquito numbers.
- One is to unleash mosquitoes pre-infected with Wolbachia, a bacterium that impairs their ability to transmit Zika, and makes males sterile. The hope is those males will mate with wild females but produce no offspring, shrinking the size of the next generation.
- Release mosquitoes sterilised with radiation, though this may make them less appealing suitors.
- The trouble with such ideas is that they give evolution a powerful incentive to select its way around the problem. Over time, that could make them less effective. One option that might avoid that problem is a “gene drive”, a new technique that tweaks genomes in a way that ensures that the modified, damaging traits are inherited by all of a mosquito’s offspring.
- Gene drives are highly controversial: if they work, they could give humans the power to wipe out—with minimal effort—any species that engages in sexual reproduction.