Genetic Spatiotemporal Anatomy of Plasmodium vivax Malaria Episodes in Greece, 2009-2013

Abstract

An influx of immigrants is contributing to the reemergence of Plasmodium vivax malaria in Greece; 1 persistent focus of transmission is in Laconia, Pelopónnese. We genotyped archived blood samples from a substantial proportion of malaria cases recorded in Greece in 2009-2013 using 8 microsatellite markers and a PvMSP-3α gene fragment and plotted their spatiotemporal distribution. High parasite genetic diversity with low multiplicity of infection was observed. A subset of genetically identical/related parasites was restricted to 3 areas in migrants and Greek residents, with some persisting over 2 consecutive transmission periods. We identified 2 hitherto unsuspected additional foci of local transmission: Kardhítsa and Attica. Furthermore, this analysis indicates that several cases in migrants initially classified as imported malaria were actually locally acquired. This study shows the potential for P. vivax to reestablish transmission and counsels public health authorities about the need for vigilance to achieve or maintain sustainable malaria elimination.

Keywords: Greece; Plasmodium vivax; PvMSP-3α; genetic spatiotemporal anatomy; malaria; microsatellite marker; migrants; parasites; transmission.

Figure 1

Geographic origin of Plasmodium vivax cases analyzed, Greece, 2009–2013. The 2 foci of transmission are Laconia and Kardhítsa (in bold). Size of dots is proportional to number of cases. Samples from Attica were distributed widely throughout this large regional unit, which includes Athens.

Figure 2

Frequency distribution of Plasmodium vivax allelic variants and lengths or subtype of genetic markers, by geographic location, Greece, 2009–2013. The frequencies for microsatellite markers MS1 (A), MS5 (B), MS7 (C), MS8 (D), MS12 (E), MS20 (F), m1501 (G), and m3502 (H) and gene fragment msp3 (I) are calculated separately for the samples from each of the 3 geographic sets: Laconia (n = 68), Kardhítsa (n = 12), and the rest of Greece (n = 38).

Figure 3

Temporal representation of the occurrence of Plasmodium vivax haplotypes, Greece, 2009–2013. Data for each region (Laconia, Kardhítsa, and rest of Greece) are depicted. Samples are indicated by shapes: in Laconia, squares indicate Greece residents and pentagons migrants; in Kardhítsa and rest of Greece, circles indicate Greece residents and hexagons migrants. Colors indicate haplotype families: La-1, yellow; La-4, blue; La-5, red; La-6, green; Gr-1, maroon; Gr-4, dark blue; and Ka, purple. Haplotype numbers are given inside shapes. The x-axis time scale for each year was stretched to accommodate the higher number of cases reported during the transmission season, with January, February, March, April, November, and December compressed. Lines joining 2 samples indicate isolates collected from the same person. Truncated vertical lines indicate the 3 samples collected in 2012 from persons considered exposed in the previous year: 1 relapse of a 2011 case and 2 patients with symptom onset in 2012 whose exposure was attributed to the 2011 transmission period. Dates of symptom onset of 2 patients tested in 2012 (green hexagons, haplotypes 28 and 29) were unknown and were arbitrarily assigned date August 1. Further details of samples are provided in online Technical Appendix 1 Tables 1–3 (https://wwwnc.cdc.gov/EID/article/24/3/17-0605-Techapp1.xlsx).