Pest exterminators fumigate a common area underneath an apartment block in the Bedok North district of Singapore, 01 September 2016.

A health expert warned Tuesday of a possible double whammy of increasing Zika and dengue fever cases in Singapore.

Professor Dale A Fisher, head of infectious diseases in Singapore's National University Hospital, believes that there is a possibility a patient could be infected with both Zika and dengue fever.

"We still have a lot to learn, but there is no reason to suspect that prior infection with one virus will increase the severity of illness when infected later with a different virus," he told dpa.

As of Monday, the number of dengue fever cases in Singapore at 11,343 had surpassed the number of cases in the whole of 2015, at 11,286.

Meanwhile, the latest figures from Singapore's Health Ministry show 275 people have been infected with Zika as of Tuesday evening.

Although Fisher said the spread of both viruses is difficult to project due to Zika only being discovered through intensive detection by health authorities, he believes the mosquito population carries a multiplier effect.

"The viruses can co-circulate in a population. Whether an individual mosquito is co-infected is not as relevant as the fact that now our mosquito population is infected by both viruses," he said.

Both viruses are spread in Singapore by the Aedes mosquito.

In February, Singapore's National Environment Agency warned of more dengue fever cases in the coming months, with an anticipated 30,000 cases by year-end.

Speaking today at the 28th Association of South-East Asian Nations (ASEAN) plenary in Laos, Singapore Prime Minister Lee Hsien Loong urged ASEAN countries to work together to fight a long battle against Zika.

"We should prepare ourselves for a possibly extended campaign against Zika, but ensure that the region remains open and connected for business and trade," said Lee.

Patients who would like to get tested for Zika can do so beginning Wednesday at a subsidised rate of 60 Singapore dollars (44 US dollars) with doctor referral, cheaper than the normal 150-dollar rate.

Testing will continue to be free for pregnant women who show symptoms or have a male partner infected with Zika.

Beginning Tuesday, hospitals in Singapore would no longer ward Zika patients or isolate suspected patients due to such cases having "mild symptoms, similar to the experience in other countries," according to a statement Monday by the health ministry.

Two pregnant women have been diagnosed with Zika in Singapore, with one of them - a 24-year-old entrepreneur - diagnosed with dengue concurrently.

She has since been discharged after recovering from both viruses but will be back in the hospital by the end of September to check if her baby is "not growing normally," she said in an interview with the Today newspaper last week.

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