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. 2017:24:25.
doi: 10.1051/parasite/2017028. Epub 2017 Jul 11.

An outbreak of locally acquired Plasmodium vivax malaria among migrant workers in Oman

Bruno Simon  1 , Fatimata Sow  1 , Said K Al Mukhaini  2 , Seif Al-Abri  3 , Osama A M Ali  2 , Guillaume Bonnot  1 , Anne-Lise Bienvenu  4 , Eskild Petersen  5 , Stéphane Picot  6
Affiliations

An outbreak of locally acquired Plasmodium vivax malaria among migrant workers in Oman

Bruno Simon et al. Parasite. 2017.

Abstract
in English, French

Plasmodium vivax is the most widely distributed human malaria parasite. Outside sub-Saharan Africa, the proportion of P. vivax malaria is rising. A major cause for concern is the re-emergence of Plasmodium vivax in malaria-free areas. Oman, situated in the south-eastern corner of the Arabian Peninsula, has long been an area of vivax malaria transmission but no locally acquired cases were reported in 2004. However, local transmission has been registered in small outbreaks since 2007. In this study, a local outbreak of 54 cases over 50 days in 2014 was analyzed retrospectively and stained blood slides have been obtained for parasite identification and genotyping. The aim of this study was to identify the geographical origin of these cases, in an attempt to differentiate between imported cases and local transmission. Using circumsporozoite protein (csp), merozoite surface protein 1 (msp1), and merozoite surface protein 3 (msp3) markers for genotyping of parasite DNA obtained by scrapping off the surface of smears, genetic diversity and phylogenetic analysis were performed. The study found that the samples had very low genetic diversity, a temperate genotype, and a high genetic distance, with most of the reference strains coming from endemic countries. We conclude that a small outbreak of imported malaria is not associated with re-emergence of malaria transmission in Oman, as no new cases have been seen since the outbreak ended.

Plasmodium vivax est le parasite du paludisme humain le plus répandu. En dehors de l’Afrique subsaharienne, la proportion de paludisme par P. vivax augmente. Une préoccupation majeure est la réémergence de Plasmodium vivax dans les zones sans paludisme. Oman, situé dans le coin sud-est de la péninsule arabique, est depuis longtemps une zone de transmission de P. vivax mais aucun cas localement acquis n’a été signalé en 2004. Cependant, la transmission locale a été rapportée dans de petites épidémies depuis 2007. Dans ce travail, une épidémie locale de 54 cas pendant 50 jours en 2014 a été analysée rétrospectivement et des lames de sang colorées ont été obtenues pour l’identification et le génotypage du parasite. L’objectif de cette étude était d’identifier l’origine géographique de ces cas, afin de différencier les cas importés et la transmission locale. Une analyse de la diversité génétique et une analyse phylogénétique ont été effectuées en utilisant les marqueurs csp, msp1 et msp3 pour le génotypage de l’ADN des parasites, obtenu en grattant la surface des frottis. L’étude a révélé que les échantillons avaient une très faible diversité génétique, un génotype tempéré et une grande distance génétique avec la plupart des souches de référence provenant de pays endémiques. Nous concluons qu’une petite flambée de paludisme importé n’est pas associée à la réémergence de la transmission du paludisme en Oman, car aucun nouveau cas n’a été observé après la fin de la flambée.

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Figures

Figure 1.
Figure 1.
Study flow chart. Ten samples were excluded from the analysis due to lack of identification, DNA degradation, or absence of DNA extracted from scrapping. DNA sequences obtained after PCR for the Pvcsp, Pvmsp1, and Pvmsp3 alpha genes were cured to limit nucleotide errors, to keep sequences of the highest quality.
Figure 2.
Figure 2.
Molecular phylogenetic analysis by maximum likelihood method for the 18 sequences of Pvcsp protein from Oman and six reference strains. The evolutionary history was inferred by using the maximum likelihood method based on the Tamura-Nei model [36]. The tree with the highest log likelihood (−587.1315) is shown. The tree is drawn to scale, with branch lengths measured in the number of substitutions per site. The analysis involved 25 nucleotide sequences. All positions containing gaps and missing data were eliminated. There were a total of 220 positions in the final dataset. Evolutionary analyses were conducted in MEGA7 [21]. The tree was rooted on Plasmodium cynomolgi csp. Bootstrap test results are shown next to the branches.
Figure 3.
Figure 3.
Molecular phylogenetic analysis by maximum likelihood method for the 22 sequences of Pvmsp1 protein from Oman and six reference strains. The evolutionary history was inferred by using the maximum likelihood method based on the Tamura-Nei model [36]. The tree with the highest log likelihood (−880.6611) is shown. The tree is drawn to scale, with branch lengths measured in the number of substitutions per site. The analysis involved 29 nucleotide sequences. All positions containing gaps and missing data were eliminated. There were a total of 243 positions in the final dataset. Evolutionary analyses were conducted in MEGA7 [21]. The tree was rooted on Plasmodium cynomolgi msp1. Bootstrap test results are shown next to the branches.
Figure 4.
Figure 4.
Molecular phylogenetic analysis by maximum likelihood method for the 25 sequences of Pvmsp3 alpha protein from Oman and seven reference strains. The evolutionary history was inferred by using the maximum likelihood method based on the Tamura-Nei model [36]. The tree with the highest log likelihood (−2208.3432) is shown. The tree is drawn to scale, with branch lengths measured in the number of substitutions per site. The analysis involved 33 nucleotide sequences. All positions containing gaps and missing data were eliminated. There were a total of 895 positions in the final dataset. Evolutionary analyses were conducted in MEGA7 [21]. The tree was rooted on Plasmodium cynomolgi msp3a. Bootstrap test results are shown next to the branches.
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