Zika: How worried should we be?

The World Health Organisation warned on Monday that the Zika virus is set to spread throughout Asia. So far, the virus has been detected in 70 countries worldwide, including at least 19 in the Asia-Pacific region. In Singapore alone, there have been more than 400 reported cases of Zika this year. Is there cause for alarm? The Straits Times speaks to microbiologist Peter Piot, director of the London School of Hygiene and Tropical Medicine, who co-discovered the Ebola virus in 1976.

Q How worrying is the Zika situation in Singapore, and what are the chances of it becoming endemic in the country?

A We think Zika is endemic in South-east Asia, and has been in the region for decades. In Thailand and Malaysia, it certainly is, and so it's likely already endemic in Singapore as well.

Even though this outbreak is probably part of the endemic circulation of Zika, people have not been looking for it or diagnosing it until recently. For example, in the past it may have been mistaken for dengue. With the publicity around the epidemic in Latin America and the Caribbean, there has been increased surveillance and diagnosis of Zika.

However, scientists in Singapore confirmed that they have been looking for Zika for several years now.

Q Mosquitoes are responsible for more than half a million deaths every year worldwide. Why are they so hard to stamp out even in a place like Singapore - known for its extensive mosquito- eradication efforts?

A Mosquitoes have a wide range of breeding sites, which can be very small, temporary bodies of water that are easily overlooked. This makes it very hard to stamp out all mosquitoes.

Singapore has been undertaking vector-control programmes for years to reduce the risk of dengue, which is spread by the same vector, the Aedes aegypti mosquito, but it is extremely difficult to completely eradicate it.

Q Singapore announced that the strain which has been found in two Singapore patients here was not imported from Brazil. While it is of the so-called Asian lineage, the virus likely evolved from a strain that was already circulating in South-east Asia. What is the implication of this finding?

A There are two main lineages of Zika - the original lineage in Africa and the Asian lineage which probably arrived in Malaysia in the 1940s. This latter lineage has been responsible for the recent outbreaks in Micronesia, French Polynesia and Latin America, and is endemic in South-east Asia.

The outbreak in Singapore is being caused by viruses that are closely related to those previously found in Thailand and Micronesia.

Q In your opinion, which is worse - Zika, chikungunya or dengue?

A It depends on who you are. If you're pregnant, or looking to conceive, then Zika could be considered the worst due to the risk of congenital Zika syndrome.

For young children, the worst would probably be dengue, because subsequent attacks of dengue once you've contracted it are more likely to be severe, possibly leading to a fatal dengue toxic shock syndrome.

For most adults, it would be chikungunya, due to the risk of permanent joint damage.

The key point is that all three diseases are spread by the same species of mosquito. They breed around houses in small amounts of clean water.

This means everyone can play a part, by disposing of waste, discarded tyres, water butts, vases and flower pots and any other vessels that can accumulate water.

kcarolyn@sph.com.sg

This article was first published on Oct 14, 2016.
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