The Zika virus caught the world’s attention last year after experts noticed that a small percentage of women carrying the virus in Latin America were giving birth to children with microcephaly, a defect that causes malformed heads and severely stunts brain development. The virus is now endemic there, and scientists fear that caseloads may spike again during the hot, wet months of the Southern Hemisphere’s summer, which begins in December.

But although the Zika strain circulating in Latin America is originally from Asia, health experts know little about its history on that side of the Pacific. “We know the virus has been circulating in the region for the better part of 70 years, but we don’t know how extensively,” said Duane J. Gubler, an emeritus professor at the Duke-NUS Medical School in Singapore.

Zika may have been understudied for decades because there were no routine tests for it until recently, scientists say, and perhaps also because the symptoms resemble those of mild dengue fever. Another possibility, they say, is that women carrying the Zika virus gave birth to microcephalic children at home. Microcephaly was first noticed in Brazil only because doctors in neonatal intensive care units of several hospitals realized that they had far more children with the problem than they normally did, and many of the mothers reported having Zika symptoms months earlier.

But the Zika scare in Latin America has prompted a recent surge in awareness and monitoring of the virus in Asia. Health ministries across the region have reported hundreds of new infections in recent months. And in October, the World Health Organization said that the Western Pacific region was “highly likely” to report more cases — and possibly new outbreaks.