A health expert today warned 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 258 people have been infected with Zika.

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.

- dpa