(CNN) In just one week, Zika cases in Singapore have gone from zero to 258, raising concerns about a potential rapid surge in cases across Asia.

It's not yet clear why Zika has spread so suddenly in Singapore . Many of the cases are thought to be locally-transmitted by the Aedes aegypti mosquito.

On Saturday, Singapore's Ministry of Health said analysis of two cases found they had likely evolved from a strain of Zika that was already circulating in Southeast Asia. Malaysia confirmed its first case of Zika infection in a 58-year-old woman -- who had visited her daughter in Singapore -- on September 1. The country reported its first locally-transmitted case on September 3, with authorities expecting more to come.

Zika's spread

In November 2015, Brazil declared a national public health emergency as cases of suspected microcephaly continued to rise.

In February 2016, the World Health Organization announced a global state of emergency over Zika, predicting as many as four million cases by the end of the year.

Singapore is not the only country in Asia to report cases of Zika -- Thailand has also seen widespread transmission in the three months, according to the European Center for Disease Prevention and Control (ECDC).

Are humid mega-cities a hub for mosquitoes?

With 5.7 million-strong populace packed mostly in dense urban areas, Singapore doesn't immediately strike you as the kind of place that would suffer long from a Zika outbreak.

But it's the city state's high population density and humid climes that offer the perfect breeding ground for the Aedes aegypti. And these are traits shared across many cities in the region.

"In Asia, you have megacities with populations between five to 10 million people. The Aedes aegypti thrives in these densely-packed urban environments," Eng Eong Ooi, the deputy director of the Emerging Infectious Disease program at Duke-NUS Medical School in Singapore, told CNN.

"When you have high populations of people and mosquitoes, it's a good recipe for both dengue and Zika to spread," he added.

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The dengue link

Dengue is also spread by the Aedes aegypti mosquito, which Singapore goes to great lengths to control. But recent efforts to stop their spread clearly haven't worked.

In 2015, the government poured $72 million dollars into researching, preventing and educating the public on dengue, a tropical disease that triggers high fevers, headaches and skin rashes in those infected.

As well as urging citizens to wear mosquito repellent, the government recommends a " 5-step mozzie wipeout " that instructs citizens on how to get rid of any pools of stagnant water in and around their homes.

Photos: Zika virus outbreak A pest control worker fumigates a school corridor on the eve of the annual national Primary School Evaluation Test in Kuala Lumpur on Sunday, September 4. Malaysia reported its first locally transmitted Zika case on September 3. Hide Caption 1 of 29 Photos: Zika virus outbreak A banner about Zika virus is seen as ferry passengers arriving from Singapore get in line at the immigration check on September 4, in Batam, Indonesia. Hide Caption 2 of 29 Photos: Zika virus outbreak A banner is flown over the South Pointe Park area, Tuesday, September 6, in Miami Beach, Florida. Hide Caption 3 of 29 Photos: Zika virus outbreak A pest control worker fumigates drains at a local housing estate where the latest case of Zika infections were reported on Thursday, September 1, in Singapore. Hide Caption 4 of 29 Photos: Zika virus outbreak Florida Gov. Rick Scott and Florida Surgeon General Dr. Celeste Philip address the media gathered at the Miami-Dade County Department of Health as they announce five cases of Zika in a 1.5 mile area of Miami Beach on Friday, August 19, in Miami, Florida. Hide Caption 5 of 29 Photos: Zika virus outbreak Brazil's interim President Michel Temer, center right, meets with officials during Temer's first visit to the Olympic Park on Thursday, June 14, in Rio de Janeiro. The Rio 2016 Olympic Games commence August 5 amid a political and economic crisis in the country along with the Zika virus outbreak. Hide Caption 6 of 29 Photos: Zika virus outbreak Rio 2016 Chief Medical Officer Joao Grangeiro, Municipal Secretary of Health Daniel Soranz and Sub-secretary of the State for Health and Surveillence Alexandre Chieppe field questions from the media during an International Media Briefing to address the Zika virus on Tuesday, June 7, in Rio de Janeiro. Hide Caption 7 of 29 Photos: Zika virus outbreak A health worker fumigates an area in Gama, Brazil, to combat the Aedes aegypti mosquito on Wednesday, February 17. The mosquito carries the Zika virus, which has suspected links to birth defects in newborn children. The World Health Organization expects the Zika outbreak to spread to almost every country in the Americas. Hide Caption 8 of 29 Photos: Zika virus outbreak A man places a mosquito net over a bed at a home for the elderly in Masaya, Nicaragua, on Thursday, February 11. Hide Caption 9 of 29 Photos: Zika virus outbreak An Aedes aegypti mosquito floats in stagnant water inside a tire at a used tire store in Villavicencio, Colombia, on Thursday, February 4. Hide Caption 10 of 29 Photos: Zika virus outbreak A health worker fumigates an area in Caracas, Venezuela, on Tuesday, February 2. Hide Caption 11 of 29 Photos: Zika virus outbreak A lab worker exposes his arm to Aedes aegypti mosquitoes during testing at the Roosevelt Hospital in Guatemala City, Guatemala, on Monday, February 1. Hide Caption 12 of 29 Photos: Zika virus outbreak Tainara Lourenco sits inside her home in Recife, Brazil, on Friday, January 29. Lourenco, five months pregnant, lives at the epicenter of Brazil's Zika outbreak. The Zika virus has been linked to microcephaly, a neurological disorder that results in newborns with small heads and abnormal brain development. Hide Caption 13 of 29 Photos: Zika virus outbreak Dr. Angela Rocha shows brain scans of a baby born with microcephaly at the Oswaldo Cruz Hospital in Recife on Thursday, January 28. Hide Caption 14 of 29 Photos: Zika virus outbreak Alice Vitoria Gomes Bezerra, a 3-month-old baby with microcephaly, is placed in her crib by her father Wednesday, January 27, in Recife. Hide Caption 15 of 29 Photos: Zika virus outbreak A health ministry employee fumigates a home in Soyapango, El Salvador, on January 27. Hide Caption 16 of 29 Photos: Zika virus outbreak A lab technician at the Oswaldo Cruz Foundation Institute stores Aedes aegypti mosquitoes to be used in research in Recife on January 27. Hide Caption 17 of 29 Photos: Zika virus outbreak A patient suffering from Guillain-Barre syndrome recovers at a hospital in San Salvador, El Salvador, on January 27. Researchers are looking into a possible link between Zika and Guillain-Barre, a rare disorder that causes the body's immune system to attack its nerves. Hide Caption 18 of 29 Photos: Zika virus outbreak Luiz Felipe lives in Recife and is one of more than 4,000 babies in Brazil born with microcephaly since October. The drought-stricken impoverished state of Pernambuco has been the hardest-hit, registering 33% of recent cases. Hide Caption 19 of 29 Photos: Zika virus outbreak A health worker sprays insecticide under the bleachers of Rio de Janeiro's Sambadrome on Tuesday, January 26. Hide Caption 20 of 29 Photos: Zika virus outbreak A Brazilian soldier inspects a home in Recife on Monday, January 25, while canvassing the neighborhood and attempting to eradicate the larvae of mosquitoes linked to the virus. Hide Caption 21 of 29 Photos: Zika virus outbreak David Henrique Ferreira, a 5-month-old who has microcephaly, is watched by his brother in Recife on January 25. Hide Caption 22 of 29 Photos: Zika virus outbreak The larvae of Aedes aegypti mosquitoes are photographed in a lab in Cali, Colombia, on January 25. Scientists are studying the mosquitoes to control their reproduction and resistance to insecticides. Hide Caption 23 of 29 Photos: Zika virus outbreak Angelica Prato, a pregnant woman infected by the Zika virus, receives medical attention at a hospital in Cucuta, Colombia, on January 25. Hide Caption 24 of 29 Photos: Zika virus outbreak A woman walks through fumes as health ministry employees fumigate an area in Soyapango on Thursday, January 21. Hide Caption 25 of 29 Photos: Zika virus outbreak Brazilian soldiers apply insect repellent as they prepare for a cleanup operation in Sao Paulo on Wednesday, January 20. Hide Caption 26 of 29 Photos: Zika virus outbreak A researcher at the University of Sao Paulo holds a container with female Aedes aegypti mosquitoes on Monday, January 18. Hide Caption 27 of 29 Photos: Zika virus outbreak A graveyard in Lima, Peru, is fumigated on Friday, January 15. Hide Caption 28 of 29 Photos: Zika virus outbreak Aedes aegypti mosquitos are seen at the University of Sao Paulo on January 8. Researchers from the Pasteur Institute in Dakar, Senegal, came to Brazil to train local researchers to combat the Zika virus epidemic. Hide Caption 29 of 29

Controlling the spread

Experts say containing Zika requires different measures in different countries.

The Aedes aegypti's ability to breed in everything from damp flower pots to small puddles on the ground presents a particular challenge to some of the more populous nations in Asia, where sanitation and access to clean water is poor.

"In Singapore, very few people would store water in waters tanks, whereas in places where water supply is not reliable, people would have to store water in large jars that would be a good breeding site for mosquitoes," explained Ooi.

"If the water supply is not consistent and households need to rely on them, you can't just remove them. Any mosquito control program has to be effective in that particular local area."

Modeling Zika's spread in Asia

Researchers behind the study which estimated 2.6 billion people were at risk of Zika in Asia and Africa also examined countries' ability to deal with an outbreak.

"We looked at the health care capacity of a countries, the volume of travel from areas where Zika is currently circulating, and the population living in areas where Zika could be locally transmitted and found that countries like India, China, the Philippines, Indonesia, Nigeria, Vietnam, Bangladesh were highest risk," Kamran Khan, study co-author and infectious disease physician at St. Michael's Hospital in Toronto, told CNN.

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Khan wants his team's research to help governments with less-developed infrastructures and fewer health facilities to be able to deploy their resources effectively if they ever had to face a Zika epidemic.

The aim, he said, was for these countries to be prepared enough to prevent any outbreak from placing too much of a strain on already overburdened health care systems.

"It's also a call to the broader international community to say that assistance is need to address Zika as a global epidemic," he said.