A ticking time bomb. That's what some health officials say the Zika virus is in Southeast Asia.
In the past two weeks, an outbreak in Singapore has climbed from a few dozen cases to nearly 300. "They're starting to have a situation in Singapore, which is really quite worrying," Dr. Anthony Fauci from the National Institute of Allergy and Infectious Diseases said at a recent meeting on Zika at Georgetown University Law Center.
And it's true. Southeast Asia has all the right ingredients for a massive Zika outbreak.
It's home to more than 600 million people. Many are packed into densely populated cities, which often lack mosquito control. And just like Latin America, Southeast Asia has the perfect climate for the mosquitoes that transmit Zika — hot and moist.
"When you go outside in Malaysia, you get bitten everywhere. It's not like in the U.S. Mosquitoes are everywhere!" says Jamal Sam, a virologist at the University of Malaya in Kuala Lumpur.
But there's something hiding in Southeast Asia that may protect the continent's people from Zika. It's in their backyards, their flower pots and birdbaths. And this secret weapon is the exact opposite of what you might expect.
"There's lots of evidence that Zika is already present in Southeast Asia," Sam says.
That's right: Zika could protect Asia from Zika.
Scientists first detected the virus in the region in the 1960s. Over the next 50 years, multiple studies found sporadic cases across a massive swath of land — in Thailand, Cambodia, Indonesia and Malaysia.
Those studies suggest Zika has been lurking in Asian mosquitoes and possibly infecting people silently, for decades — maybe longer. And that means people in the region may already be immune to Zika.
It's almost like the people are vaccinated, Sam says. "Because once you get Zika, you probably can't get it again, probably. We don't know for sure, but that's probably true."
That natural immunity could stop — or temper — potential outbreaks, Sam says.
"It's possible," Sam says. "But it depends on how much immunity we have [in the population]. And those studies haven't really been done."
Decades ago, a few studies suggested up to 30 percent of Malaysians may have immunity to Zika. But, Sam says, no one really knows about other parts of Southeast Asia. And even that Malaysian percentage is a bit dubious.
"Those studies are old," he says. And the tests used back then — and even now — aren't good at differentiating Zika antibodies from those of similar viruses, such as dengue. "So you get a lot of false positives," Sam says.
Of course, Southeast Asia has changed over the past decade in ways that could make Zika outbreaks worse. Many countries have gone through massive development, with cities growing both up and out. Mosquitoes that carry Zika thrive in urban environments.
And the Zika virus itself has also changed over time. Viruses with RNA genes, such as Zika, are known to mutate quickly. Some scientists have worried that Zika has turned into a more dangerous form that causes birth defects
But recent studies suggest that doesn't seem to be the case, says Jasper Chan, a microbiologist at the University of Hong Kong.
"We think the Zika virus hasn't mutated that much over the years," Chan says. "We don't see very significant changes, at least, not in the key genes."
So, he says, the version of Zika in Asia will probably act similarly in people as the one in Latin America. "Microcephaly, Guillan-Barre and all the other concerns about Zika are still a threat to people in this region" — unless those people have already been infected with Zika.
So in the end, it's really a mystery about how much of a problem Zika will be in Southeast Asia. "The virus could spread explosively or not," Chan says. "We'll have to wait and see how the story unfolds."
AUDIE CORNISH, HOST:
We've watched a global health emergency unfold over the past year. An outbreak of the mysterious Zika virus began in Brazil. Since then, it's spread throughout the Western Hemisphere, and it's led to nearly 2,000 babies being born with extremely small heads and brain damage. Seventeen of them have been in the U.S. Health officials worry the same thing is happening on the other side of the world, too. NPR's Michaeleen Doucleff reports.
MICHAELEEN DOUCLEFF, BYLINE: A few weeks ago, health experts sat down at Georgetown University to talk about Zika. You might expect the focus would be on Florida where Zika has infected at least 56 people. But right off the bat, Dr. Anthony Fauci of the National Institutes of Health brought up another place with a Zika outbreak.
ANTHONY FAUCI: And I'm watching Singapore very, very carefully 'cause if you look at the numbers in Singapore, it went from a handful to, like, 50 to 80 and now there's well over a hundred cases.
DOUCLEFF: Make that more than 300 cases. Over the past few weeks, the virus has spread rapidly in Singapore. And the concern is that the outbreak could trigger an epidemic in Southeast Asia.
FAUCI: They're starting to have a situation in Singapore which is really quite worrying.
DOUCLEFF: Fauci says Southeast Asia has all the right ingredients for a massive Zika outbreak. There are more than 600 million people, many are packed into densely populated cities and just like Latin America, they have a climate that's perfect for mosquitoes that transmit Zika.
FAUCI: We know how difficult it is when you have a climate that is a semi-tropical, moist climate. To get rid of the breeding places of mosquitoes is extremely problematic.
DOUCLEFF: So on the surface, it looks like Southeast Asia is a ticking time bomb on the brink of a public health crisis. But Jamal Sam at the University of Malaya says maybe not. He's a virologist in Malaysia. We talked over Skype. He says Southeast Asia has one big difference from Latin America, which could protect it from Zika.
JAMAL SAM: There's lots of evidence that Zika is already present in Southeast Asia.
DOUCLEFF: Yep, you heard him right. Zika could protect Asians from Zika. It sounds illogical but here's why. Zika was brand new to the Americas when it started here a few years ago. But scientists first detected Zika in Southeast Asia back in the 1960s. And the virus has already shown up across Thailand, Indonesia, Cambodia and Malaysia. Jasper Chan is a microbiologist at The University of Hong Kong.
JASPER CHAN: I would say that a lot of scientists in the region agree that the Zika virus has probably been underestimated in many of these areas.
DOUCLEFF: So if Zika has been circulating in Southeast Asia for decades, why haven't we heard about all the problems it causes, the babies born with small heads, the neurological issues like Guillain-Barre? Chan says these problems could have been there all along, but no one was looking for them. The rate of birth defects is too small for anyone to notice. Brazil seems to be the exception to this and no one yet knows why.
But what this means for Southeast Asians is that Zika outbreaks could be limited to small clusters because University of Malaya's Jamal Sam says many people may already have been infected and are immune to Zika.
SAM: Probably once you get it, it's unlikely you'll get it again, probably.
DOUCLEFF: It's almost like people have been vaccinated, which means there will be fewer people in the population that will be susceptible. The problem is right now nobody knows how many Asians have been infected with Zika. That answer will determine if Zika erupts into a problem where millions of people are infected, as we've seen in Latin America, or if it just fizzles out. Michaeleen Doucleff, NPR News. Transcript provided by NPR, Copyright NPR.