Has Zika circulated quietly in Asia for decades?

[Gert van der Hoek]

• Nov 24, 2016

CHICAGO/BANGKOK – Zika’s rampage last year in Brazil caused an explosion of infections and inflicted a crippling neurological defect on thousands of babies — an effect never seen in a mosquito-borne virus.

It also presented a mystery: why had a virus that had been little more than a footnote in the annals of infectious diseases taken such a devastating turn in the Americas? How had Africa and Asia, where Zika had quietly circulated for decades, escaped with no reports of major outbreaks or serious complications?

Scientists initially theorized that Zika’s long tenure in Africa and Asia may have conferred widespread immunity. Or, perhaps older strains were less virulent than the one linked in Brazil to more than 2,100 cases of microcephaly, a birth defect characterized by arrested brain development.

Now, amid outbreaks in Singapore, Thailand, Vietnam and other parts of Southeast Asia, a much graver explanation is taking shape: perhaps the menace has been there all along but neurological complications simply escaped official notice.
The question is driving several research teams, according to leading infectious disease experts and public health officials.

“Zika is Zika until proven otherwise. We assume that all Zikas are equally dangerous,” said Dr. Derek Gatherer, a biomedical expert at Lancaster University in Britain.

One recent review of studies suggests 15 to 40 percent of the population in some African and Asian countries may have been previously infected with Zika, said Alessandro Vespignani, a professor of health sciences at Northeastern University in Boston.

Researchers also believe it is possible that microcephaly went undetected in parts of Asia and Africa where birth defects weren’t well tracked.

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