Abstract
BackgroundSingapore has been certified malaria free since November 1982 by the World Health Organization and despite occasional local transmission, the country has maintained the standing. In 2009, three clusters of malaria cases were reported in Singapore.MethodsEpidemiological, entomological and molecular studies were carried out to investigate the three clusters, namely Mandai-Sungei Kadut, Jurong Island and Sembawang.ResultsA total of 29 malaria patients, with no recent travel history, were reported in the three clusters. Molecular analysis based on the msp3α and msp1 genes showed two independent local transmissions: one in Mandai-Sungei Kadut and another in Sembawang. Almost all cases within each cluster were epidemiologically linked. In Jurong Island cluster, epidemiological link remains uncertain, as almost all cases had a unique genetic profile. Only two cases shared a common profile and were found to be linked to the Mandai-Sungei Kadut cluster. Entomological investigation found Anopheles sinensis to be the predominant Anopheline in the two areas where local transmission of P. vivax was confirmed. Anopheles sinensis was found to be attracted to human bait and bites as early as 19:45 hrs. However, all Anopheles mosquitoes caught were negative for sporozoites and oocysts by dissection.ConclusionInvestigation of P. vivax cases from the three cluster areas confirmed the occurrence of local transmission in two areas. Although An. sinensis was the predominant Anopheline found in areas with confirmed transmission, the vector/s responsible for the outbreaks still remains cryptic.
Highlights
Singapore has been certified malaria free since November 1982 by the World Health Organization and despite occasional local transmission, the country has maintained the standing
It has been reported that 60% of vivax malaria cases occur in Southeast Asia and the Western Pacific, and that India contributes substantially to this regional disease burden [4]
In 2006, 13 vivax malaria cases involving foreign workers from endemic countries were reported at the Jurong island [7]
Summary
Epidemiologic findings Using nested PCR assay, P. vivax was confirmed to be the only malaria parasite present in all 20 samples sent to EHI for further analysis. The same situation was found in Sembawang Both the msp3a RFLP and msp sequence analysis of Jurong Island cases showed that only two cases were molecularly linked, and they were linked to the Mandai-Sungei Kadut outbreak. It seems that the high transmission potential may be due to the high human biting rate of the mosquito Results from this investigation strongly suggests that An. sinensis, which has never been implicated as a vector in Singapore, was the predominant Anopheline in Mandai-Sungei Kadut and Sembawang. In these areas, there was substantial molecular evidence of local transmission and multiple breedings of the Anopheline were found. Additional file 2: Mosquito species obtained from the malaria outbreak areas
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