How to keep Zika at bay

Deet is the most effective ingredient in insect repellents and is safe for pregnant women to use

Account coordinator Nicole Conceicao, who is eight months pregnant, used to apply insect repellent before she left her flat in Tampines, which was a dengue hotspot.

Now, with news of the Zika virus being detected in several South- east Asian countries, including Singapore's first reported case last week, she has been taking the repellent out with her and applying it a few more times a day.

Ms Conceicao, who is in her late 30s, says: "I am probably being kiasu, but people could get the virus when they travel regionally and bring it home without knowing it."

It is understandable why she prefers to be safe than sorry. The Zika virus poses a serious threat to pregnant women as it can lead to their children having birth defects.

The virus is linked to microcephaly, a rare neurological disorder in which the size of the baby's head is much smaller than that of a normal baby's.

  • Safe and effective insect repellents for pregnant women


    Active ingredient: 15 per cent Deet

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    Active ingredient: 7 per cent Deet

    Price: $4.20


    Active ingredient: 19.2 per cent Picaridin

    Price: $12.10


    Active ingredient: 9.3 per cent Picaridin

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    • Prices from Guardian Health & Beauty

The virus is spread by the bite of infected Aedes mosquitoes, similar to dengue.

That is why many pregnant women, such as Ms Conceicao, want to avoid being bitten and bug sprays have become part of their daily routine.

But for some mothers shopping for the right spray, the question is: to Deet or not to Deet?

Deet (N, N-Diethyl-meta-toluamide) is a synthetic chemical that repels insects.

It has been reported that prolonged exposure and excessive application of the substance is adverse to health and could cause skin irritation and rashes.

But most doctors here say products containing Deet and another newer synthetic chemical, Picaridin, are safe for use in pregnancy. Picaridin is also known as Icaridin.

Associate Professor Thoon Koh Cheng, chairman of the infection control committee at KK Women's and Children's Hospital, advises pregnant women to apply repellents with no more than 20 per cent Deet or Picaridin.

He says studies show that Deet, which has been around for almost 50 years, is still the most effective ingredient in repelling insects.

The effectiveness and duration of protection increase with the concentration and plateaus at about 50 per cent.

But doctors warn against applying repellent directly on the face and on cuts on the skin.

"They can spray it into their palms and rub it on their face, but avoid going too close to the eyes, nose and mouth," says Mr Niron Naganathar, a drug information pharmacist at Changi General Hospital.

He says: "Ingesting Deet may cause nausea, vomiting and abdominal pain while inhaling it may cause difficulty in breathing. Spraying it on the face may also irritate the eyes."

Of course, to put things in perspective, Singapore is still generally safer than other places with ongoing Zika transmissions.

The Healthy Ministry has already issued an advisory for pregnant women to consider postponing any "non-essential" travel to countries with outbreaks.

If they must travel to affected areas, they should take strict precautions against mosquito bites.

Obstetrician and gynaecologist Henry Cheng from Mount Elizabeth Novena Hospital says expectant mothers should see a doctor before travelling, and monitor themselves for two weeks after returning to Singapore.

Most people infected with the Zika virus do not have symptoms, but those who do usually develop them within three to 12 days after the mosquito bite.

Symptoms are similar to dengue and include fever, rashes, joint pain, headache and conjunctivitis (red eyes).

A negative blood test does not rule out Zika infection, as the virus stays in the bloodstream for only up to seven days, after which it is undetectable.

Routine prenatal care, including ultrasound scans to check foetal growth and well-being, is needed to monitor pregnant women who are suspected of a Zika infection, he adds.

While Zika is predominantly spread by the Aedes mosquito, some studies have shown that an infected man may have the virus in his semen.

Spouses of pregnant women who have returned from Zika hotspots should practise safe sex by using condoms or abstain from sex throughout their wives' pregnancy.

Dr Cheng adds: "The risk of a Zika infection being sexually transmitted is still not clear, though there have been a few reported cases."

But normal contact between the couple will not expose the unborn baby to the virus, he says.

Corporate communciations executive Charissa Tan, 29, who got married last October, said the single case of Zika here has not put her off from trying for a baby.

She lives in Siglap, which is a dengue hotspot.

"Unless the risk is significant, I would take precautions against mosquito bites rather than stop trying to get pregnant. This is because the chances of getting pregnant decreases with age."

How to avoid mosquito bites

The Zika virus is linked to microcephaly, a rare neurological disorder in which the size of the baby's head is much smaller than that of a normal baby's.

"It is associated with developmental delay during infancy and childhood and, in severe cases, the child may have visual and hearing problems and seizures," says Professor Victor Samuel Rajadurai, head of neonatology at KK Women's and Children's Hospital.

The Sunday Times asks some doctors for tips on avoiding mosquito bites for pregnant women:

1 Wear long-sleeved clothing when outdoors for a prolonged period.

2 Avoid using perfumes, especially scents that are fruity or floral, as they attract mosquitoes.

3 At home, use bed nets or window screens to prevent mosquitoes from entering.

4 Repellents with Deet are the most effective protection against insects. To be safe, those expecting should avoid sprays with more than 20 per cent concentration of Deet. That provides about four hours of protection.

5 Do not spray directly on the face and on cut skin.

6 Natural or plant-based insect repellent oils such as citronella, lemongrass or eucalyptus can provide some protection against insects, but are less effective than those with Deet as the active ingredient.

7 It is best to apply the repellent in the morning or evening. The Aedes mosquito is generally most active during daylight hours, with peak biting at dawn and dusk.

• Information from Dr T.C. Chang, obstetrician and gynaecologist at Thomson Medical Centre; Mr Niron Naganathar, drug information pharmacist at Changi General Hospital; Guardian Health & Beauty; Associate Professor Thoon Koh Cheng, chairman of KK Women's and Children's Hospital infection control committee; Associate Professor Tan Thiam Chye, head of inpatient services at KKH division of obstetrics and gynaecology; and National Environment Agency

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A version of this article appeared in the print edition of The Sunday Times on May 22, 2016, with the headline Which mosquito repellents are best for pregnant women . Subscribe