SINGAPORE: The Zika virus strains found in the two locally transmitted cases from the Sims Drive-Aljunied Crescent cluster were not recently imported from South America. Rather, these strains have sequences similar to those which have been circulating in Southeast Asia since the 1960s, before they spread to French Polynesia in 2013 and subsequently to Brazil in 2015.
This analysis was according to the sequencing study conducted by the Ministry of Health's National Public Health Laboratory (NPHL) and A*STAR's Bioinformatics Institute, with the findings revealed on Thursday (Sep 8).
“What we have demonstrated that is there are enough differences at the gene level to show that (the strain) is not imported from South America”, said Dr Raymond Lin, head of the NPHL, at a press briefing.
In terms of how severe the Southeast Asian strain is and whether it causes microcephaly – a congenital condition associated with incomplete brain development – Dr Lin said there is currently no evidence to indicate that it is more or less severe than the South American strain.
“From what we see, the viruses are very similar. There might be fine differences, there might be more mutations but currently there is no evidence at all to suggest that it's less severe or more severe; whether there is less or more likelihood of getting microcephaly,” said Dr Lin.
“The correlation of virus strains with specific clinical manifestations will take long-term, careful epidemological studies as well as experimental studies in research laboratories,” he added.
Zika was first detected in a rhesus monkey living in 1947 in the Zika Forest of Uganda, Africa. The infection was later identified in humans in Uganda and the United Republic of Tanzania in 1952, NPHL and A*STAR said at the briefing.
On how the findings would help develop a vaccine against the Zika virus, Dr Lin said: “If we know that a large part of it is very similar to the virus in other parts of the world, it’s important to know whether the vaccine developed in one part of the world can be used here.”
Dr Sebastian Maurer-Stroh, Senior Principal Investigator of A*STAR's Bioinformatics Institute, said knowledge about the various strains could also help in future testing of vaccines and various treatment strategies.
“When we talk about the Asian version or the South American version – these viruses are still very similar. So it also means that our immune response will be quite similar to them. It has implications if someone develops a vaccine against the Brazilian strain, it should also work against the Southeast Asian version. So this also relates to natural immunity of people,” said Dr Maurer-Stroh.
But he also emphasised that more research needs to be done to understand the implications of the virus.
The findings will be made available on public databases for the benefit of the global scientific community, including the World Health Organisation.
Eight new cases of locally transmitted Zika were confirmed on Wednesday (Sep 7), bringing the total number of confirmed cases in Singapore to 283, according to MOH.