When Zika first emerged as a public health emergency in Brazil early last year, to most people it came out of nowhere. Yet the virus had been known to the scientific community for at least 70 years after it was first discovered in a remote forest in Uganda that shares its name. So what exactly happened between its initial discovery, and the recent epidemic that has made it so serious a disease?
Researchers have now conducted one of the most detailed genetic analyses of the virus, tracking it as it spread from the Zika forest, throughout Asia, and finally into the Americas, and have been able to pinpoint at least two mutations that may have contributed to its current severity in the New World. They have found that there are multiple strains of the virus, some of which are worse than others, and that this could be vital to know if another epidemic was to emerge.
So at what point then did the Pacific strain develop its severity? The researchers think that they may have found an answer.
They noticed that there were certain mutations in the viral RNA that started appearing as Zika island-hopped across the Pacific. When they then looked at this in detail, they found the spread of the mutations matched the sudden appearance of microcephaly and Guillain-Barré syndrome in French Polynesia.
The mutations themselves that occurred were found to be related to the part of the genome that codes for the coating of the virus, as well as what is known as the “untranslated regions.” The coating influences how well the virus infects a host cell, while the untranslated regions are related to what tissue of the body they infect.
They found that some of the mutations mimicked human proteins involved in the development of sensory organs in the fetus, while another helped it to infect stem cells. This could help explain why the Pacific strain has been so severe and damaging when pregnant mothers are infected.
While its initial discovery may have been one in Africa, the researchers think that the virus’s history in Asia is far more significant. “Our results indicate that Zika may have deep ancestry in Asia that has been under-recorded,” said Daniel Janies, who co-authored the paper published in the journal Cladistics. “For example, not all the recent global outbreaks of Zika appear to result from a simple linear chronology of travel from the most recent past outbreak.”
This implies that there have been multiple different strains, causing multiple different outbreaks. They point to a recent outbreak in Singapore of the virus, which shows that it is only distantly related to the strain that is causing so much strife in the Americas. It means that if and when another outbreak occurs, its origin will dictate how damaging the effects will be.