Scientists here have confirmed that the Zika virus found in two locally transmitted cases in the Alju- nied/Sims Drive cluster was not from South America.
However, more research is needed in order to understand the link between the virus strains - not sequenced before - and other health conditions such as microcephaly and Guillain-Barre syndrome.
"This (the virus strains) seems like something that has been in our region for a long time but it doesn't mean the clinical outcomes and all that are not linked," said Associate Professor Raymond Lin, head of the National Public Health Laboratory at the Ministry of Health.
"Chances are that we have to assume they share fairly similar potential for how they cause disease."
Prof Lin, together with Dr Sebastian Maurer-Stroh, senior principal investigator at the Agency for Science, Technology and Research's Bioinformatics Institute, shared their findings yesterday after sequencing three cases of Zika found here.
The first was from a Singapore permanent resident found in May to have been infected after he came back from Brazil. Based on the sequence, his strain was similar to those found in South America.
The two other strains found in locally transmitted cases, however, likely evolved from a strain circulating in South-east Asia since the 1960s even though they share the same lineage with South American strains. They are believed to have originated in Asia.
Infectious diseases specialist Paul Tambyah said the Zika virus had not been detected in previous surveillance studies but could have been in Singapore all along.
"The main thing is that the link between the current Singapore outbreak and Brazil is remote - a few virus generations away," he added.
"What this specifically means is that no one returning from Rio or South America brought the virus into Singapore. It came in from somewhere else - maybe it was under the radar in Singapore all along or perhaps somewhere in South-east Asia."
Apart from helping to track the spread of the virus globally, the findings would be helpful for developing Zika vaccines.
The link between microcephaly and Zika surfaced after Brazil reported outbreaks of the virus. Infectious disease experts here agree that it is too early to conclude the strains detected here are less likely to cause birth defects.
There is no need for those who are pregnant to panic even though they have to be cautious, said Prof Lin. "If any pregnant woman is infected with Zika, we'll need to just follow up closely and see what the outcome is."