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FIGHTING ON EVERY FRONT: Fogging, insecticide application, and household and worksite inspection are ongoing exercises in the fight against Zika. We have also moved to biological control with the introduction of mosquitoes laced with Wolbachia bacteria, which do not kill the mosquitoes but instead reduce their ability to transmit dengue, Chikungunya and Zika.

Zika and the carrier connection

The mosquito is the primary vector, or bus, for the Zika virus and the sooner its habitat is destroyed, the safer it will be especially for pregnant women who are the most vulnerable
Sep 10, 2016 5:50 AM

ZIKA has hit our shores on Aug 27 this year; the first locally transmitted case of the Zika virus has been diagnosed and she is unlikely to be the first patient with Zika on our island. In an epidemic, we call the first patient the Index case but we could not do so for this 47-year-old Malaysian female. It is likely that Zika has arrived on our shores way before she was diagnosed.

How did we end up in this situation? This is because the mosquito of which there are three species called Culex, Anopheles and Aedes; can carry a variety of bugs.

The Aedes carries Dengue, Chikungunya and Zika, the Anopheles carries Malaria and the Culex carries Japanese B encephalitis and Filiariasis. Filiariasis may not be familiar to Singaporeans but you may recall images of patients who have an enormous misshapened leg suffering from a disease called elephantiasis.

The mosquito, or vector, is essentially a bus and these bugs are passengers along for the ride. In retrospect, it was a matter of time before Chikungunya and Zika boarded our local bus. What is frightening is that there are many more passengers that can technically get on the bus. A prime example is yellow fever from the Americas and Africa.

In Singapore, we are currently battling with the Zika onslaught. The virus is mainly asymptomatic and 80 per cent of the victims have no symptoms. Those who have symptoms will have mild fever, rash, joint pains, muscle aches, headaches and conjunctivitis.

A word about the rash; it is flat and not raised; the red patches tend to spread and join together; this characteristic is also called a confluent rash. The rash tends to start early with the fever, may be on the face and maybe itchy in some.

Mild disease

If most of the patients have no symptoms and the disease is mild, why are we worried about symptomatic patients? The answer is that symptomatic patients allow us to pick up the disease pattern so we can figure out where the clusters are and where to fight the mosquitoes. The asymptomatic cases are the problem because they don't know that they have the virus and yet the mosquito can bite them and transmit the virus.

Some have compared Zika to SARS but really Zika is a mild disease and is unlikely to kill the patient. Hence the latest decision to keep the patients at home instead of in the hospital. However, what is the frightening aspect is the effect on the unborn. The images of microcephaly are enough to give us sleepless nights.

I am of the opinion that what threatens the future unborn generations of Singaporeans are a clear and present threat. The linkage of microcephaly to the Zika virus has been examined carefully and the conclusion is that there is a strong link with infection in the first trimester of pregnancy.

In a study of a Zika outbreak in French Polynesia in 2014, the risk of microcephaly was estimated at 1 per cent risk if the mother contracted the virus in the first trimester. Many in the medical community criticise this figure but it was a brave attempt of the Pasteur Institute researchers to put a figure to the risk.

To contrast this figure, the base risk of microcephaly in the population is about 6 per 10,000 babies born or 0.006 per cent. Nevertheless, one microcephaly case is one too many in a country with low birth rates to begin with. Yet, to fight this enemy would require GPs and obstetricians to be vigilant in diagnosing the threat, testing of pregnant women with symptoms and follow-up of the pregnancies with serial ultrasounds.

A word on testing: we are currently using DNA amplification process called PCR (polymerase chain reaction) to look for the virus in blood and urine. We found that the test is good at picking up the virus for a week to twelve days in the blood after the patient has symptoms.

Testing the urine is a little better as we can pick up the virus for two to four weeks after the patient has symptoms. We do not test the semen but apparently the virus can be in the semen for up to sixty days. Hence, we have told male patients to abstain for six months or to practice safe sex. For women who have the infection, we are asking them to abstain for 8 weeks on recovery.

We are hampered currently as we are lacking a good antibody test for Zika; in most viral diseases, we have an antibody test called IgM that can detect recent infection and another antibody test called IgG that can detect infection that occurred a long time ago. We need a m ore effective antibody test. The DNA method is expensive and tedious; needing five hours to get a result and initially costs about S$400 for the test. The cost of the test is currently free or heavily subsidised for suspect cases including pregnant women.

Protocol of testing

We also need to find a way to test our pregnant women who have no symptoms and to develop a protocol of testing them to avoid birth defects.

Finally we need to get rid of the "bus" that is carrying the nasty passengers. We probably have one of the most effective mosquito eradication programmes in the world (circa 1966 to 1981) and yet the vector is still causing between 10,000 to 20,000 cases of dengue annually in recent years.

The vector has modified its behaviour and is able to breed in very small amounts of water. The community is really gearing up to attack the mosquito and this is seen in mobilising the community with "Mozzie Wipeout", dengue volunteers and personal behaviour modification. Meanwhile fogging, insecticide application, and household and worksite inspection carry on and we have finally moved to biological control with the introduction of mosquitoes laced with Wolbachia bacteria. These bacteria do not kill mosquitoes but instead reduce their ability to transmit dengue, Chikungunya and Zika.

The battle rages on as we speak; fear and anxiety is the order of the day but with society mobilised and the government agencies, medical sector and biotechnology sector all being aligned as well as with heightened personal responsibility from each Singaporean, I am optimistic we will overcome this threat to our country, people and the unborn generation of future Singaporeans.

  • Dr Chong is a physician at Singapore Medical Specialists Centre and chairman, Private Practice Committee of the SMA.
  • This series is produced on alternate Saturdays in collaboration with Singapore Medical Specialists Centre.