Background: Case management of imported malaria within the context of malaria pre-elimination is increasingly
considered to be relevant because of the risk of resurgence. The assessment of malaria importation would provide
key data i) to select countries with propitious conditions for pre-elimination phase and ii) to predict its feasibility.
Recently, a sero-prevalence study in Djibouti indicated low malaria prevalence, which is propitious for the
implementation of pre-elimination, but data on the extent of malaria importation remain unknown.
Methods: Djiboutian plasmodial populations were analysed over an eleven-year period (1998, 1999, 2002 and
2009). The risk of malaria importation was indirectly assessed by using plasmodial population parameters. Based on
5 microsatellite markers, expected heterozygosity (H.e.), multiplicity of infection, pairwise Fst index, multiple
correspondence analysis and individual genetic relationship were determined. The prevalence of single nucleotide
polymorphisms associated with pyrimethamine resistance was also determined.
Results: Data indicated a significant decline in genetic diversity (0.51, 0.59, 0.51 and 0 in 1998, 1999, 2002 and 2009,
respectively) over the study period, which is inconsistent with the level of malaria importation described in a
previous study. This suggested that Djiboutian malaria situation may have benefited from the decline of malaria
prevalence that occurred in neighbouring countries, in particular in Ethiopia. The high Fst indices derived from
plasmodial populations from one study period to another (0.12 between 1999 and 2002, and 0.43 between 2002
and 2009) suggested a random sampling of parasites, probably imported from neighbouring countries, leading to
oligo-clonal expansion of few different strains during each transmission season. Nevertheless, similar genotypes
observed during the study period suggested recurrent migrations and imported malaria.
Conclusion: In the present study, the extent of genetic diversity was used to assess the risk of malaria importation
in the low malaria transmission setting of Djibouti. The molecular approach highlights i) the evolution of Djiboutian
plasmodial population profiles that are consistent and compatible with Djiboutian pre-elimination goals and ii) the
necessity to implement the monitoring of plasmodial populations and interventions at the regional scale in the
Horn of Africa to ensure higher efficiency of malaria control and elimination