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Keep up the anti-mozzie war for two more months

During the three-week, all-out fight against the Zika virus, dengue cases caused by the same Aedes mosquito went down by nearly half. This shows that anti-mozzie vigilance pays off. Such vigilance has to continue for the next two months of the peak Aedes breeding period.

The Zika outbreak galvanised the nation.

Now, three weeks after the announcement of the first known local infection of the virus caused by the Aedes mosquito, interest appears to have died down. Mosquito fatigue has set in.

If people go back to the "I'm not affected, I don't care" mode, then all the good work in the early part of this month goes down the drain - because we are still in the peak period of mosquito breeding and viral transmission which normally runs from June to October.

While it is early days yet, the number of dengue infections since Zika was announced on Aug 28 tells a story.

They have been falling: from 308 cases of dengue the week local Zika infection was announced, to 241 cases the following week and 175 last week.

This shows that when everyone makes the effort, the spread of mosquito-borne viral diseases can be, if not stopped, at least reduced significantly.

What have falling dengue numbers got to do with Zika, you may ask.

Very simply, the same Aedes mosquito spreads both Zika and dengue, and also chikungunya.


The female mosquito needs blood to breed and usually feeds off several people, as it lays eggs in batches, hence helping to spread the viral diseases from one person to another.

So even if the concern about the Zika virus has eased, except among pregnant women, the fight against its spread should continue because it can make a world of difference to the number of people here getting sick from the Aedes mosquito.

If we don't worry about Zika, we should worry about dengue, because dengue is arguably the more serious disease. Seven people have already died from dengue this year.


Zika is a relatively mild disease for the majority of people who just need a little rest to recover. Dengue, on the other hand, has one in five


people infected needing hospital care.

About 11,800 people have been diagnosed with dengue this year, and close to 2,400 people have landed in hospital as a result. This is no small number, especially given the bed crunch public hospitals are struggling with.

The pity of it all is that such suffering, and the seven deaths, were truly needless, since they were largely caused by a lack of care on the part of people in their homes, various agencies in charge of public areas, and construction firms at their sites.

Having said that, it is true that the Aedes mosquito has adapted well to city living and needs only a little bit of clean water - just a teaspoon is enough - to breed. And it needs just a week to grow from egg to adult.

In spite of everything we might do, it is almost impossible to totally eradicate them, and there are probably more mosquitoes in the country than there are people.

But we can keep the numbers low.

Just three weeks of concerted effort has seen dengue numbers almost halved. Based on current trends, this would suggest that the number of people needing to be hospitalised would fall from 60 a week to 35 a week.

Those infected know that dengue is a painful disease. Symptoms include high fever, severe headaches, joint and muscle pain, and nausea and vomiting.

When dengue raged in 2012 and 2013, there were weeks when more than 800 people had to see a doctor after coming down with dengue. Early this year, infections crossed the 600-a-week figure. And that was during the "off-peak" season for the disease.

In fact, experts had been predicting a boom year for dengue this year, given the high numbers in the normal "low" period, with infections tipped to cross the 30,000 mark for the first time.

So while public anxiety about the Zika virus appears to have abated somewhat as the virus does not cause serious illness in most infected people, this is not the time to let down our guard.

Yes, fatigue from checking our homes every day for mosquito- breeding areas and from the constant fogging does set in, and it's difficult to maintain full vigilance all the time.

But this is definitely not the time to relax and get careless over mosquito breeding.

This includes people who might be leaving their homes empty when they go on vacation during the coming school holidays.

In the three weeks since Zika surfaced locally, the National Environment Agency has had to break into 24 premises - after repeated attempts to contact the owners to allow its officers in to check for mosquito breeding failed - and found three with water and larvae.

The Aedes mosquito generally stays within 50m to 150m of its place of birth, and rarely goes more than 500m away in its lifetime.

So if the breeding was found in the homes of people away on holiday, they would return to find mosquitoes waiting to bite. Or the victims could be their neighbours.

As for the Zika virus, while Zika appears to be a relatively harmless disease for the majority, for a small number it could prove extremely severe.

It can cause birth defects in babies whose mothers get infected in early pregnancy.

The birth abnormality most linked to Zika are babies born with microcephaly or exceptionally small heads and attendant mental and physical retardation, as well as something called congenital Zika syndrome which causes disfigured faces, poor eyesight, seizures, extremely stiff muscles and low intelligence.

The risk of an infected woman having a baby with problems ranges from less than 1 per cent to 13 per cent, and currently no one can account for the wide variation.

There is also fear that Zika can damage the nervous system of those infected, given the strong link to Guillain-Barre syndrome where a person's muscles suddenly weaken significantly, with recovery taking weeks, sometimes even years, and some people possibly suffering from residual effects for the rest of their lives.

There is also the recent worry that the virus could affect the brains of adults, but more subtly than in a foetus. No one knows what the long-term effects of that might be.

All this should give added impetus for everyone to remain vigilant for at least the next two months, until cooler weather sets in and mosquitoes find it harder to breed, to avert a mosquito population boom.

Worldwide, mosquitoes kill an estimated 725,000 people a year. We should not let the Aedes mosquitoes here add to those numbers.

A version of this article appeared in the print edition of The Straits Times on September 22, 2016, with the headline 'Keep up the anti-mozzie war for two more months'. Print Edition | Subscribe