Threat of Zika-linked microcephaly looms
Concern over the disease has been kept to a minimum in Southeast Asia, but with two Thai babies infected and Singapore’s outbreak spiking it must be taken seriously
There is a high risk of the mosquitoborne Zika virus causing microcephaly among babies in Southeast Asia as it has in Brazil, health experts have warned. The spread of Zika in some countries in Southeast Asia in recent months has not caused much panic as the disease had been mild. Moreover, until recently there had not been any recorded case of microcephaly, which causes smaller heads than normal in some babies of women who have been infected during pregnancy. But that lull could end after Thailand on Friday became the first Asian country to report microcephaly in two babies due to Zika.
Two experts — one from the United States and another from Hong Kong — said there is a big risk that the virus circulating in Southeast Asia could pose the same dangers as the one that wreaked havoc in Brazil.
“It is possible the Asian lineage [of Zika] is milder, but we do not have any evidence of that. My best guess would be they pose similar dangers,” said Justin Lessler, an infectious diseases expert from the Johns Hopkins Bloomberg School of Public Health in the United States.
Jasper Chan of the University of Hong Kong’s Department of Microbiology warned that there are reasons to believe from lab observations and genetic information that caution should be taken.
“The African lineage, the Southeast Asian lineage and the American lineage of the Zika virus are all possible potential agents that can be related to the same clinical manifestations that we worry about,” Mr Chan said.
“Some people have asked us whether we think the Asian lineage or the Western lineage would be less harmful to the babies or to the patients, and we say that we do not know, we need to observe, but at least from the lab testing we know that they behave very similarly, so that is something that we need to watch out for.”
In recent weeks there were news reports of an Asian “strain” of the Zika virus that has been circulating in Southeast Asia for a few decades. The possibility that some people in the region might have developed an immunity to it had given hope that the virus might not be so virulent as in Brazil.
Singapore announced a Zika outbreak in late August with more than 200 cases in the central-eastern part of Singapore, mostly concentrated in a construction site. Since then, the number of infections has swelled to around 400 locally transmitted infections, with at least 16 pregnant women reported to have caught the virus.
An epidemic of any infectious disease would be a big blow for the tiny islandstate with its dense urban population of 5.6 million. The country plays a key role as a business and financial hub, and as a transit hub for travellers and cargo. It also has a thriving tourism industry.
On Sept 8, Singapore’s Health Ministry posted a statement on its website on the result of laboratory sequencing of the virus from a couple of local cases jointly with a state-owned scientific research institute. The sequencing found that it shares similarities with the “strains of Zika virus which have been circulating in Southeast Asia since the 1960s, before the viruses spread to French Polynesia in 2013 and subsequently to Brazil in 2015”.
It said the virus “belongs to the Asian lineage and likely evolved from a strain that was already circulating in Southeast Asia”.
Soon after, a university professor in Malaysia’s Sabah state in Borneo said that because the virus had been circulating in Southeast Asia for some decades, there is a possibility that people in the region had developed antibodies that could help to protect them from the virus.
Mr Chan said, “Of course any virus or any pathogens or any microbes would continue to mutate, so it’s not unexpected that you have a few mutations here and there but we and other groups did not find anything very peculiar that lead us to think that they may behave differently.
“I personally do not believe that ... these Asian cases would behave very differently clinically from what we have seen in South America, so I do think we need to watch out because it’s just that nobody really paid attention in the old days, and the number of infections have been quite low in the past.”
On the existence of the African lineage, the South American lineage, and the Southeast Asian lineage, Mr Lessler said, “As far as we know, they all descend from Africa, but we do not know if they have any difference in their clinical or transmission characteristics, hence, we do not know if they are different enough to be termed as different strains.”
He added that “numerous uncertainties remain” with regards to the virus.
Mr Lessler said that if people in the region have already have acquired immunity, then the virus might spread slowly in the region instead of flaring up like a wildfire as in Brazil. “What we don’t know is how long Zika has been around in the region and whether or not there is any underlying immunity to it,” Mr Lessler said.
“We know that it has at least been introduced in the region in the past. Often asymptomatic, it has been circulating at a very, very low level in the region for a while and we are only noticing it now because we are looking, inspired by the outbreak in the Americas.”
He said it is possible that the virus has been simmering in the region for a long time and “we may never have noticed the severe side effects. I would be surprised if we see something as dramatic as what we have seen in the Americas, but I think the potential for a significant outbreak still exist.”
Mr Chan also said that the risk of a Zika epidemic could be very high in Southeast Asia. “The climate is suitable for the virus. Secondly, Southeast Asia is highly densely populated in many countries. When you have such a large population within a small area, then the transmission of different pathogens is very efficient. Thirdly, many of our countries in Southeast Asia do have mosquito vectors that can transmit the Zika,” he explained.
Earlier last week, the US Centres for Disease Control and Prevention advised pregnant women to consider postponing non-essential travel to Southeast Asia countries which have reports of Zika virus infection from local transmission.
The countries it singled out are Brunei, Myanmar, Cambodia, Indonesia, Laos, Malaysia, Maldives, the Philippines, Thailand, East Timor and Vietnam. On Aug 30, it had warned pregnant women or those trying to get pregnant to avoid travel to Singapore. KYODO