Viruses from local infections from three different strains so incidents aren't linked
Lee Hui Chieh, Straits Times 4 Aug 08;
THE number of people infected by chikungunya here continues to climb but, for now, the virus causing the mosquito-borne disease has probably not gained a foothold in Singapore.
The National Environment Agency (NEA) said its tests showed that the viruses that caused the first three incidents of local infection - in Little India, Teachers' Estate off Upper Thomson Road, and Farrer Road - belonged to different strains.
This means that the three incidents were not linked, said Dr Ng Lee Ching, head of the NEA's Environmental Health Institute, which conducted the tests.
Each time, the infection had probably been sparked by someone getting infected overseas bringing one particular strain of the virus here, she added.
And each time, the infection was stamped out so that strain did not spread further.
The institute's scientists established that the first three incidents had occurred separately by mapping the genetic code, or DNA, of the viruses in patients' blood samples. They found that the viruses were related to the one that caused huge outbreaks in islands in the Indian Ocean in 2006, where deaths were reported. But each was of a distinctly different strain.
It was unlikely that the second and third strains had mutated from the first in such a short time, Dr Ng said.
Public health officers have gone all out to track patients and destroy mosquito breeding sites. This is to ensure that chikungunya does not become as common here as dengue.
Having both similar diseases entrenched here will complicate diagnosis, treatment and containment.
Singapore is at risk as it hosts many travellers, the virus-transmitting Aedes mosquito flourishes here, and people here have no immunity against chikungunya.
It was spread for the first time in Singapore, when 13 people living or working in Little India contracted it in January.
In June, a retiree and her maid living in Teachers' Estate, and an expatriate housewife living in Farrer Road were infected.
Joining the list of local cases last month: A housewife living in Jalan Jelita off Holland Road, two foreign workers working and living in a site at Kranji Way, and a local delivery driver who went there.
Another 31 people here caught the disease while abroad this year; before that, 13 others had been infected overseas over 2006 to 2007.
The rise in the number of chikungunya cases here, both local and imported, mirrors a global trend, Dr Ng said.
Recently, outbreaks have been reported more often in Malaysia, Indonesia and India, and in previously chikungunya-free areas such as Italy.
The reasons for the upswing in infections are not known. But scientists believe that a contributory factor is the emergence of a certain strain of the chikungunya virus, which has mutated such that it can be carried by another sub-species of the Aedes mosquito - the Aedes albopictus.
Previously, the virus' main vehicle of infection was the Aedes aegypti, which is also behind most dengue cases.
The institute's scientists have yet to study virus samples
from this month's local cases but will be doing so.
Appealing to the public to help eliminate mosquitoes and their breeding sites, Dr Ng said: 'Chikungunya is not endemic here yet, so we still have a chance to keep it out. It is easier to do that than to try to get rid of it when it is established.'
