The Zika virus appears to be spreading rapidly in Singapore, with 115 confirmed cases as of Wednesday, according to government officials. At least one pregnant woman is among them.
And a woman from Malaysia who had recently been in Singapore has tested positive for the infection, the country’s health minister announced Thursday.
The virus’s emergence in the Asian city-state is raising lots of questions that will likely preoccupy experts on the World Health Organization’s Zika Emergency Committee, which meets Thursday.
The most pressing: Is this a sign the epidemic virus racing through the Americas will do the same in Asia and Africa? Will pictures of Brazilian babies with microcephaly give way in coming months to images of African and Asian babies whose brains have been ravaged in the womb by this virus?
The expert committee may ask Duane Gubler, a WHO adviser and one of the world’s leading authorities on arboviruses — viruses spread by mosquitoes and ticks.
STAT asked him first.
His answer: “We don’t know at this point.”
We also asked Dr. Tom Frieden, director of the Centers for Disease Control and Protection, shortly after he got off the phone with the head of the World Health Organization, Dr. Margaret Chan.
“One of the things that we’re really struggling with is what’s going to happen in Asia and Africa? We really don’t know,” Frieden said. “I’ve been running public health agencies for 15 years. We’ve done everything from post-9/11 anthrax to H1N1 [pandemic flu], SARS, MERS. This is really complicated.’’
Zika — an oddball virus that causes little illness in most people and devastating disease in some fetuses, that is spread by mosquitoes and by sex, that did nothing for decades and then exploded in South America — is one vexing little beast.
Nearly a year after it started to gain international notice, the answers to crucial questions remain frustratingly out of reach.
In the decades between Zika’s first spotting — in Uganda in 1947 — and its big bow on the world stage in 2015, the virus was occasionally reported in Africa and Asia.
Did it spread constantly, infecting lots of people who are now immune? Or did it mostly infect primates, leaving most people alone — and vulnerable to a new outbreak? No one knows.
Answers to those questions would allow you to start to formulate an educated guess about whether and which African and Asian countries are next on Zika’s global itinerary.
With many viruses, a simple blood test would answer these questions. Researchers would gather blood specimens from people in a bunch of different places and use them to pinpoint where Zika had circulated.
But there’s nothing simple about Zika. The antibodies it generates are currently almost indistinguishable from antibodies to its cousin viruses — things like dengue, West Nile, Japanese encephalitis, and yellow fever. They’re also quite similar to the antibodies generated by the live-virus vaccines used to protect against all those illnesses.
So it’s really hard to tell whether an individual with those antibodies has been exposed to Zika or to one of these cousins, said Dr. Robert Tesh, director of the World Reference Center for Emerging Viruses and Arboviruses at the University of Texas Medical Branch in Galveston.
Nevertheless, over the years researchers have tried to determine how much immunity to Zika exists in parts of Africa and Asia. Based on the work, the WHO thinks Zika has spread widely.
“The understanding we have is it’s been pretty much everywhere in the world,” said Christopher Dye, an infectious disease epidemiologist who is director of strategy in the office of the WHO director general.
If that’s true, that doesn’t mean countries without current outbreaks, like Vietnam and the Philippines, or Angola and the Central African Republic, are in the clear. Zika may have infected a few people, leaving wide swaths of the population vulnerable. Or it may have come through decades ago, but not recently.
If 60 year-olds are immune in Zambia but people of child-bearing age are not, Zika is still a big threat there.
“There are real fears that the strain from the Americas, where there has been a lot of microcephaly, could work its way back across the African continent, causing large numbers of cases of microcephaly or Guillain-Barré syndrome in places where Zika was present historically but hasn’t been seen for a long time,’’ Dye said.
“We just can’t rule that out at the moment with the information that we’ve got. and therefore, we need really to be vigilant about this.”
That’s why the WHO has watched so closely as first Cape Verde — islands west of Senegal — and Guinea Bissau, in West Africa, reported cases of Zika and microcephaly, as well.
The virus responsible in Cape Verde was the Asian strain, but Dye said early word from Guinea Bissau suggests that the African family of viruses — not previously associated with birth defects — may be to blame there.
“It would be momentous — and that’s not too strong a word — if we were to discover that an African strain now was causing infections that led to microcephaly and possibly other severe neurological disorders,” he noted.
Efforts to get to answers about Zika have been hobbled by a lack of funding, in the United States and elsewhere, Dye said.
“We’re working with a much smaller budget than anticipated,’’ he said. “The world doesn’t perceive Zika to be such a big threat as was, say, Ebola. And I think the world is acting accordingly.”
Solving another puzzle would also help to assess Zika’s potential.
Does prior infection with closely related viruses make Zika infection worse? Or do those antibodies actually provide some protection that might block Zika infection, or tone it down if it occurs?
Depending on whom you ask, you’ll get a different theory. Some researchers are worried dengue antibodies up the ante while others say those types of prior infections could lower the risks.
So without answers, we’re into the realm of theories. Here are a couple:
Gubler believes Zika has spread broadly in the past. But he suspects the virus caused sporadic cases, not big outbreaks. Those would have been spotted, said Gubler, a professor emeritus in the emerging infectious diseases program at the Duke-NUS Medical School. (He recently moved back to the United States from the school’s outpost in Singapore.)
His theory is that the virus circulating in the Americas, while still from the Asian family of Zika, has some small genetic changes that make it nastier. And Gubler suspects the virus causing cases in Singapore is that version.
“My bet would be that this is an introduced strain that has greater epidemic potential,” he said, adding he wouldn’t be surprised to see it spread from Singapore to other parts of Asia and, if it reaches southern China, maybe Africa. China has substantial economic interests in and sends large numbers of Chinese workers
Dye thinks the Singapore cases are caused by viruses from Asia, but ones that have not undergone the changes that are allowing Zika to damage fetuses and occasionally cause Guillain-Barré syndrome in adults.
“I’m guessing … it’s going to be the Asian strain that has traditionally been around in Malaysia and Indonesia and the Philippines and so forth,” he said.
Dr. Kamran Khan’s research focuses on the potential for spread of diseases using global airline travel data. An infectious diseases doctor at Toronto’s St. Michael’s Hospital, he doesn’t venture a guess on Zika immunity levels in Africa and Asia. But if there is substantial susceptibility, and if the outbreak virus is introduced, the conditions for spread are ripe, he said.
“You’ve got the same kinds of circumstances you saw in Brazil, which are high population density,” mosquitoes, and poverty, Khan said.
Dylan Scott contributed to this article