Zika Virus Became Lethal Thanks To A Single Mutation

A child affected with microcephaly caused by the Zika virus in Brazil. Jao Souza/Shutterstock

The Zika virus is responsible for severe brain abnormalities in thousands of children across the world, and yet it was not always a dangerous virus. When it was discovered in 1947, it was mostly harmless.

Chinese researchers have now pinpointed this change to the single mutation of a gene, which likely happened in 2013. As they report in Science, the genetic change is located at position S139N of the virus's RNA, making it a lot more efficient at killing developing brain cells.

The researchers compared Zika viruses collected in Cambodia in 2010 with the more virulent specimen from 2015. The more recent one exhibited seven changes to the genetic code, each responsible for altering the surface proteins of the virus by a single amino acid.

The researchers created multiple clone versions of the 2010 Zika virus, each altered with a single one of the witnessed mutations. They then used the resulting strain to infect fetal and newborn mice, with the S139N mutation responsible for a greater amount of brain cell destruction. Even in human neural progenitor cells, the mutated version was a much better killing machine than its 2010 counterpart.  

“The fact that this change in behavior can be almost wholly attributed to a single amino acid change in one of the virus’ surface proteins is remarkable,” Professor Jonathan Ball, from Nottingham University, told LA Times. Professor Ball studies genetic changes in the Ebola virus. “This data, as well as evidence from other viruses like Ebola, shows us that the smallest of genetic changes can have a major impact on virus behavior.”

The Zika epidemic was an international emergency for nine months in 2016, and while it stopped being so last November, the threat remains for many millions of people around the world. To date, around 1.5 million individuals have been infected in Brazil alone.

The rapid change of the virus is also the reason why there was no vaccine. There was no reason to look for one when the virus wasn’t deadly. Now, two vaccines are currently in development for Zika. So far, they have only been tested in mice, but they seem to provide full protection in the rodents.

[H/T: LA Times]

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