Dengue cases down but chikungunya up in Singapore

39 caught chikungunya locally last week; disease has been made notifiable
Salma Khalik, Straits Times 23 Dec 08;

WITH intensified efforts this year, Singapore's fight against dengue appears to have paid off, with 25 per cent fewer cases than last year.

However, a newly emerged Aedes mosquito-borne illness is causing fresh concerns. Chikungunya cases continued their upward trend, with more than 40 cases a week in the past three weeks.
Of the 43 cases diagnosed last week, 39 caught the virus locally, while the other four imported cases were from Malaysia.

Last Friday, the Ministry of Health made chikungunya a notifiable disease.

Although doctors have already been informing the ministry of all cases since the end of 2006, when Singapore saw its first imported chikungunya case, the change means that doctors could be penalised with fines or jail terms for not doing so.

A ministry spokesman said this will enable the ministry to monitor the disease more closely. A circular has gone out to all doctors informing them of the change.

The appearance of locally transmitted chikungunya infections in Singapore this year also worries infectious diseases experts.

Although no one has died of the infection, chikungunya, unlike dengue, can be very debilitating. There is also the risk that it could become endemic, which means the disease would be here to stay, with no chance of wiping it out.

The Health Ministry said the disease has not become endemic yet, as a large number of cases is still from overseas.

Until this year, the few cases were all imported. But by the middle of this month, 388 people had caught the virus locally. A further 158 people who were infected were bitten by mosquitoes while overseas, primarily in Malaysia.

The areas where people here are getting bitten by the Aedes mosquito have also spread from the northern part of the island to places such as Bedok Reservoir and Tampines in the east.

Cases have also been on the increase, rising sharply since the end of July.

Given the current rates of infection, Singapore is likely to end the year with more than 600 chikungunya cases.

A spokesman for the National Environment Agency (NEA) said the Aedes albopictus mosquito, which is the main carrier of this virus, lives in forests and other heavily vegetated areas.

This makes it 'a challenge to remove as many breeding habitats as possible in such areas,' she said.

She added that the current rainy season is unlikely to be the cause of the increased rates. Instead, it has more to do with 'the movement of infected cases and the susceptibility of the population'.

The NEA spokesman said it is fighting chikungunya the same way it does dengue - by finding and destroying mosquito breeding spots and educating the public about stagnant water.

She added that the early and intensive exercise against the Aedes mosquito this year has staved off an anticipated dengue epidemic. Dengue epidemics tend to come in five to six year cycles.

So far this year, 6,424 people have become sick with dengue and dengue haemorrhagic fever, 2,183 fewer than last year. 'Earlier this year, it was predicted that Singapore would experience major dengue outbreaks and the situation would be worse than last year,' she said.

But instead of going up, the number of infections had gone down significantly, due to the $200,000 a day spent fighting the scourge this year.

'This reversal in dengue trend, the first time in three decades, is a result of the enhanced dengue control strategy put in place by NEA,' said the spokesman.

What is chikungunya

# SYMPTOMS: Sudden high fever, headache, fatigue, nausea, vomiting, muscle pain, rash and joint pain.

These are almost similar to symptoms for dengue, the other Aedes mosquito-borne viral disease, except the joint pains for chikungunya can be excruciating, last for months and, in some cases, for more than a year.

While painful and debilitating, the infection is not life-threatening.

# TREATMENT: There is no vaccine against it or medicine that cures it. Treatment is only for symptoms such as fever or pain.

# TRANSMISSION: The culprit for dengue tends to be the Aedes aegypti while the Aedes albopictus is more likely to spread chikungunya.

However, both types of mosquitoes can spread both diseases.

# INCUBATION: It usually takes three to seven days from the time a person is bitten by an infected mosquito for symptoms to appear.

However, people can sometimes become sick just two days after being bitten, or as late as 12 days after.

# SPREAD: The disease is spread when a mosquito bites an infected person. The virus replicates in the mosquito and is passed on to people subsequently bitten.

# PREVENTION: The best way to stop the spread of the disease is to prevent mosquitoes from breeding. This year, the National Environment Agency spent close to $200,000 a day and has a team of 500 people doing just that.

A mosquito needs just a small spoonful of stagnant water to breed. The A. aegypti breeds well in indoor receptacles but the A. albopictus prefers forests and places with high vegetation.

Those infected should wear long sleeves and long dresses or pants and use insect repellent to prevent getting bitten again by mosquitoes, which could continue the chain of transmission.