Malaria in Singapore

Singapore was declared malaria-free in 1982 by the World Health Organization, although up to 270 cases are reported each year since 2000. These are mainly expatriates or residents who have acquired the infection from abroad. For example, one of the largest clusters in recent history occurred in a group of Nigerian students who had been brought into Singapore by a local informatics company for a 2-year training program. Out of the 72 Nigerian youths who came in 2005, 8 were symptomatic for falciparum malaria, but a further 13 were only picked up on screening the cohort. Locally-infected (or "authocthonus") cases do occur sporadically, but are rare.

Since May this year, however, we have had three separate clusters of vivax malaria at Jurong Island (n = 9), Sungei Kadut/Mandai estate (n = 16) and Sembawang (n = 4). It is unclear if these clusters are related, since they occur at different parts of Singapore. Because the infection is caused by Plasmodium vivax - one of two malaria species with a long latent liver ("hypnozoite") phase - it is plausible that some of the cases among the foreign workers may be incidental rather than occurring as a result of local transmission. NEA has not reported the capture of any malaria-infected anopheline mosquitoes during its surveillance of these sites.

These clusters highlight clearly the vulnerability (and resistance) of Singapore to malaria. Plasmodium falciparum and vivax are endemic to the region, including in nearby offshore islands such as Pulau Tekong. No formal malaria eradication campaign had been conducted in Singapore prior to or after 1982 (although there were "antimalarial drainage systems" and "oiling cycles" from the 1910's to 1980's, and vector/case surveillance/control from the 1970's - the last of which is now directed against the Aedes mosquito and dengue/chikungunya), and the Anopheles mosquito can still be found in parts of Singapore.

At the same time, we continue to bring in foreign workers from malaria-endemic countries, some of who will inevitably be carriers of the parasite. The cost of screening each worker routinely is prohibitive at this point, hence cases and small outbreaks will continue to occur.

Singapore's "resistance" to malaria is a result of urban development and the continued failure of the local anopheline mosquitoes to adapt to a more urban environment (unlike the very successful Aedes mosquito). So there will never be a malaria outbreak on the scale of dengue or even chikungunya in Singapore. Because it is a far more dangerous disease, however, it is important to diagnose and institute appropriate treatment early.