Malaria outbreak worsens with two more cases

The type of mosquito responsible unlocated; partial immunity in some people may aid spread
Salma Khalik, Straits Times 12 Jun 09;

THE outbreak of malaria in Singapore took a turn for the worse yesterday, with two more people - including another Singaporean - coming down with the potentially deadly disease.

This brings the total number of people infected to 17 - all men.

Of these, 15 are foreign workers living in dormitories - either in the Sungei Kadut/Mandai area in the north, or Jurong Island in the south.

The two Singaporeans are a full-time national serviceman who the Health Ministry said was likely to have been bitten while in camp, and a 51-year-old worker in Mandai Estate.

Worryingly, the type of Anopheles mosquito responsible for the outbreak of malaria has not been located yet despite sweeps of the two areas where the infections have occurred.

This could mean that the mosquitoes may continue to breed and infect more people.

The outbreak of malaria here is the worst since 2006, when 13 people came down with it.

In that instance, however, a victim infected overseas was bitten by an Anopheles mosquito which succeeded in spreading the parasite to 13 other people on Jurong Island and the nearby Pulau Busing.

The current outbreak, on the other hand, has not only infected more people, but has occurred in two distinct locations, making it more difficult to contain.

Another worry this time around: Many foreign workers here come from countries where malaria is endemic, and might have been infected several times previously.

This gives them a sort of 'semi-immunity', said Dr Lim Poh Lian, a senior infectious disease consultant at the Communicable Disease Centre (CDC). This could make the chain of transmission harder to break.

She explained that those who have had previous infections might become only mildly sick if bitten by an infected mosquito. In such cases, they might not be diagnosed as having malaria.

However, the parasites which cause the disease would be in their blood following the bite. If they are bitten by another Anopheles mosquito, the disease could spread.

Meanwhile, the National Environment Agency (NEA) is pursuing efforts to stamp out the disease.

It said it is investigating how the transmission took place, and is continuing with intensive search-and-destroy operations on the ground.

These include thermal fogging in the night, as the mosquitoes responsible for spreading malaria are active in the evening and early morning.

Singapore was declared malaria-free in 1982, when it eradicated sustained local transmissions of the disease.

It has maintained this status for almost three decades by swiftly ring-fencing any imported cases to prevent the disease from spreading.

Malaria can be cured if diagnosed early and treated. Delays in treatment can result in death. Symptoms include fever, headache, chills and vomiting.