| Summary: | Abstract Background Following malaria elimination, Sri Lanka was free from indigenous transmission for six consecutive years, until the first introduced case was reported in December 2018. The source of transmission (index case) was a member of a group of 32 migrant workers from India and the location of transmission was their residence reporting a high prevalence of the primary vector for malaria. Despite extensive vector control the situation was highly susceptible to onward transmission if another of the group developed malaria. Therefore, Mass Radical Treatment (MRT) of the group of workers for Plasmodium vivax malaria was undertaken to mitigate this risk. Method The workers were screened for malaria by microscopy and RDT, their haemoglobin level assessed, and tested for Glucose 6 phosphate dehydrogenase deficiency (G6PD) using the Care Start RDT and Brewers test prior to treatment with chloroquine (CQ) 25 mg/kg body weight (over three days) and primaquine (PQ) (0.25 mg/kg/day bodyweight for 14 days) following informed consent. All were monitored for adverse events. Results None of the foreign workers were parasitaemic at baseline screening and their haemoglobin levels ranged from 9.7–14.7 g/dl. All 31 individuals (excluding the index case treated previously) were treated with the recommended dose of CQ. The G6PD test results were inconclusive in 45% of the RDT results and were discrepant between the two tests in 31% of the remaining test events. Seven workers who tested G6PD deficient in either test were excluded from PQ and the rest, 24 workers, received PQ. No serious adverse events occurred. Conclusions Mass treatment may be an option in prevention of reintroduction settings for groups of migrants who are likely to be carrying latent malaria infections, and resident in areas of high receptivity. However, in the case of Plasmodium vivax and Plasmodium ovale, a more reliable and affordable point-of-care test for G6PD activity would be required. Most countries which are eliminating malaria now are in the tropical zone and face considerable and similar risks of malaria re-introduction due to massive labour migration between them and neighbouring countries. Regional elimination of malaria should be the focus of global strategy if malaria elimination from countries is to be worthwhile and sustainable.
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