A total of 279 pregnant women in the United States and its territories have tested positive for the Zika virus, prompting a personal plea from President Barack Obama for more funds to fight the outbreak which is spreading fast.

First seen in Brazil last year, the mosquito-borne virus has now been reported in 60 countries and territories.

Mr Obama has warned that if the outbreak is not handled now, the US will have "bigger problems on the back end". While the White House had called for US$1.9 billion (S$2.6 billion) to fight the threat, the Senate last week approved only US$1.1 billion, while the House of Representatives voted to redirect about US$662 million from Ebola funding to Zika research.

Public health officials, already critical of the world's slow response to the Ebola epidemic, are pressing for faster action against this new disease, which can cause microcephaly, a birth defect in babies, and also neurological disorders in adults.

The US Centres for Disease Control and Prevention has said it will issue weekly reports on all pregnant women who have the infection, instead of focusing on those who presented symptoms. It is also increasing its testing capacity, as mosquito season in the summer months approaches.

Although there has been no mosquito-borne transmission in the US itself, experts say it is only a matter of time before this happens in the gulf states such as Florida and Texas.

These states have already ramped up mosquito control efforts, increasing the number of staff on the ground and reminding residents to quash mosquito-breeding grounds.

Zika will also top the agenda during the World Health Organisation's (WHO) annual assembly this week. WHO director-general Margaret Chan said it will ask the assembly for increased funding for the next two years, in order to contain the spread of newly emerging threats such as Zika.