Billions of people are at risk from the deadly Zika virus following outbreaks in Africa and Asia, according to a scientific study.
Close to 70 countries have now reported instances of the virus transmitted by mosquito bites.
The government in Singapore has reacted with a mass fumigation as 151 cases, including two pregnant women are treated by doctors.
The study fears the number of cases will rise worldwide as travel between infected and non-infected areas peaks in the coming months.
Warm temperatures also promote the longevity of mosquitos carrying the virus, increasing the chances of catching Zika.
Pregnant women with the symptoms risk their babies born with abnormally small heads – a condition called microcephaly.
Researchers explained that the risk of the virus spreading among more than 2 billion people in the countries most at risk was likely due to difficulties in detecting the illness and a lack of medical resources.
The team from the London School of Hygiene and Tropical Medicine and universities in Oxford, Britain, and Toronto, Canada, pinpoint an influx of air passengers either infected by the virus or carrying mosquitos in their luggage as the main risk for spreading Zika.
They rank the Philippines, Vietnam, Pakistan and Bangladesh as the main black spots for the disease.
Zika was first identified as a serious public health risk in Brazil in the run up to the Olympic Games in Rio.
Hundreds of soldiers took to the streets to fumigate suspected infected homes and businesses while a higher than average number of abnormal births thought to be triggered by the virus was recorded.
Dr Oliver Brady, one of the research team from the London School of Hygiene and Tropical Medicine, said: “Countries such as India, Indonesia and Nigeria are predicted to be at highest risk of Zika introduction with up to 5,000 passengers a month arriving from Zika endemic areas.
“Should Zika be imported into these areas the impact on their health systems could be very severe.”
Brady also noted that Zika is not a new medical problem but has affected parts of Africa and Asia for years and that the spread may be less than predicted as some populations may already have built an immunity from low level exposure.