7th September 2016
In the past 10 days, the Ministry of Health (MOH) has notified the public that there has been local transmission of Zika virus in 3 main areas namely in the Aljunied/Sims Drive, Bedok North and Joo Seng areas. In addition, there is a possible new cluster in Bishan and there have been an increasing number of “isolated” cases that were not linked to these clusters. Local transmission of Zika virus has now spread beyond the original cluster and we should be concerned that Zika infection is now more widespread in Singapore.
As of September 6th, 2016, there were 275 cases of confirmed Zika infection in Singapore. From the evolution of this outbreak, it appears that Zika infection in Singapore had possibly started in the first few weeks of August and spread quickly. With intensive outbreak investigations, the number of cases notified has escalated from one on August 26th to 275 by September 6th. This is contrast to May 2016 when the first case of imported Zika was reported. In that imported case, the patient had travelled to Brazil and following his return to Singapore, he felt ill and was diagnosed to have Zika virus infection. No cases were subsequently reported around where he stayed in the vicinity of Watten Estate, Casa Perla, Hillcrest Arcade, The Arcadia and Watten Hill condominiums.
The implication of local transmission in Singapore is more serious for the following reasons.
- 1. We have a persistent and well established Aedes mosquito population in Singapore despite years of intensive vector control efforts
- 2. Our population is immunologically naïve to Zika virus infection and once established, there is concern that this virus will spread quickly within the population in Singapore
It is important to reiterate that the Zika virus infection in most individuals will be mild and often asymptomatic. Rarely, neurological complications such as Guillain-Barre syndrome may occur. So far, the cases notified in Singapore have caused a mild illness and MOH has now amended the clinical management policy. Patients with confirmed Zika infection will not be routinely admitted for monitoring purposes.
Pregnancy And Asymptomatic Infection
The major concern is the impact on women who are of childbearing age. If they are currently pregnant in the first trimester of pregnancy and who are living, working, or studying in a known cluster area, they are likely to be very concerned. The difficulty is that an estimated 80% of patients infected with Zika virus will NOT display any symptoms and may not seek medical attention. It is inappropriate to advise all pregnant women in Singapore to undergo ”routine” Zika testing. In contrast, any pregnant woman who has symptoms that fit the case definition regardless of where they work, stay or study in Singapore should be strongly advised to undergo Zika testing. In addition, consideration should be made for asymptomatic pregnant women living, working or studying in known cluster areas to be offered Zika testing.
The Risk Of Fetal Infection And Microcephaly
It is important to state that Zika infection in a pregnant woman does imply that there will be fetal infection. In addition, fetal infection does not always equate to development of severe neurological damage like microcephaly. The risk of microcephaly has been estimated to be between 0.8% to 13%. The risk of microcephaly varies according to when fetal infection has occurred. Other factors including environment, other co-infections are being actively evaluated on their contribution to the development of microcephaly.
If a couple living in a known cluster area is planning pregnancy, they will also be concerned. If a woman of childbearing age is infected, the current recommendation is for her to defer pregnancy for at least 8 weeks. In contrast, a man who is infected with Zika may transmit the virus through the sexual route for the next 6 months! Planning pregnancy is such a personal issue that each case needs to managed differently.
Testing For Zika Infection
At this time, we have sensitive nucleic acid amplification tests to detect Zika virus infection in the first 14 days of illness. Beyond that period, we do not have a reliable test to detect ”infection” as the usual serological testing methods may ”cross react” with other Flavivirus such as dengue
Singapore Zika Strain
MOH has announced that the Zika strain identified in Singapore is of Asian lineage and is ”different” from the strains in Brazil. Zika is a positive sense single stranded RNA virus. These “differences” are likely to be evaluated extensively by researchers over the next few weeks and months. At this time, it will be premature to speculate the implications of this ”different strain”.
Possibility Of Zika Vaccine
The recent outbreaks of Zika virus infection from 2007 until now have all been due to the Zika virus of Asian lineage. It may be feasible to obtain an effective vaccine using existing vaccine platforms. However, it will be the first vaccine against Zika virus and it will need to undergo extensive safety testing. Important research questions will include the safety of such vaccines when administered to pregnant women. If a live attenuated virus strain is used, how long will pregnancy have to be deferred after vaccination.
We still have a lot of gaps in our knowledge for Zika virus infection and the situation is rapidly evolving. Updates will be provided on this website when more scientific evidence becomes available.