Genotyping Plasmodium vivax isolates from the 2011 outbreak in Greece

Genetic Structure of Introduced Plasmodium vivax Malaria Isolates in Greece, 2015-2019

Greece has been malaria-free since 1974, after an intense malaria control program. However, as Greece hosts migrant populations from P. vivax malaria-endemic countries, there is a risk of introducing the disease to specific vulnerable and receptive areas of the country. Knowledge of the genetic diversity of P. vivax populations is essential for understanding the dynamics of malaria disease transmission in a given region. We used nine highly polymorphic markers to genotype 124 P. vivax-infected archived DNA samples from human blood specimens referred to the NMRL from all over Greece throughout 2015-2019. The genotypic variability of the samples studied was noted, as they comprised several unique haplotypes, indicative of the importation of a large number of different P. vivax strains in the country. However, only a few events of local transmission were recorded. Genotyping revealed and confirmed the same clusters as those identified through epidemiological investigation. In only one introduction event was the index case found. No sustained/ongoing malaria transmissions in/between the studied regions or during consecutive years or additional foci of local transmission were observed. Genotyping is an important component in assisting malaria surveillance, as it provides information concerning the patterns of introduction and the effectiveness of implemented malaria control and elimination measures.

Investigation of an airport-associated cluster of falciparum malaria in Frankfurt, Germany, 2022

Airport malaria is uncommon but increasing in Europe and often difficult to diagnose. We describe the clinical, epidemiological and environmental investigations of a cluster of airport malaria cases and measures taken in response. Three Frankfurt International Airport employees without travel histories to malaria-endemic areas were diagnosed with Plasmodium falciparum malaria in Germany in 2022. Two cases were diagnosed within 1 week, and the third one after 10 weeks. Two cases had severe disease, all three recovered fully. The cases worked in separate areas and no specific location for the transmissions could be identified. No additional cases were detected among airport employees. In June and July, direct flights from Equatorial Guinea, Nigeria and Angola and one parcel originating in Ghana arrived at Frankfurt airport. No vector-competent mosquitoes could be trapped to identify the source of the outbreak. Whole genome sequencing of P. falciparum genomes showed a high genetic relatedness between samples of the three cases and suggested the geographical origin closest to Ghana. A diagnosis of airport malaria should prompt appropriate and comprehensive outbreak investigations to identify the source and to prevent severe forms of falciparum malaria.

Influx of diverse, drug resistant and transmissible Plasmodium falciparum into a malaria-free setting in Qatar

BACKGROUND

Successful control programs have impeded local malaria transmission in almost all Gulf Cooperation Council (GCC) countries: Qatar, Bahrain, Kuwait, Oman, the United Arab Emirates (UAE) and Saudi Arabia. Nevertheless, a prodigious influx of imported malaria via migrant workers sustains the threat of local transmission. Here we examine the origin of imported malaria in Qatar, assess genetic diversity and the prevalence of drug resistance genes in imported Plasmodium falciparum, and finally, address the potential for the reintroduction of local transmission.

METHODS

This study examined imported malaria cases reported in Qatar, between 2013 and 2016. We focused on P. falciparum infections and estimated both total parasite and gametocyte density, using qPCR and qRT-PCR, respectively. We also examined ten neutral microsatellites and four genes associated with drug resistance, Pfmrp1, Pfcrt, Pfmdr1, and Pfkelch13, to assess the genetic diversity of imported P. falciparum strains, and the potential for propagating drug resistance genotypes respectively.

RESULTS

The majority of imported malaria cases were P. vivax, while P. falciparum and mixed species infections (P. falciparum / P. vivax) were less frequent. The primary origin of P. vivax infection was the Indian subcontinent, while P. falciparum was mostly presented by African expatriates. Imported P. falciparum strains were highly diverse, carrying multiple genotypes, and infections also presented with early- and late-stage gametocytes. We observed a high prevalence of mutations implicated in drug resistance among these strains, including novel SNPs in Pfkelch13.

CONCLUSIONS

The influx of genetically diverse P. falciparum, with multiple drug resistance markers and a high capacity for gametocyte production, represents a threat for the reestablishment of drug-resistant malaria into GCC countries. This scenario highlights the impact of mass international migration on the reintroduction of malaria to areas with absent or limited local transmission.

The Importance of an Active Case Detection (ACD) Programme for Malaria among Migrants from Malaria Endemic Countries: The Greek Experience in a Receptive and Vulnerable Area

Greece has been malaria-free since 1974. In October 2011, following an outbreak of 36 locally acquired malaria (LAM) cases in Evrotas Municipality, a Pro-Active Case Detection (PACD) program for malaria was implemented among migrants from malaria-endemic countries, to support early diagnosis and treatment of cases. We evaluated the PACD program for the years 2012–2017 using indicators such as the number of locally acquired cases, the detection rate/sensitivity and the timeliness of diagnosis and treatment. We visited each migrant home every 7–15 days to screen migrants for malaria symptoms, performing Rapid Diagnostic Tests (RDTs) and blood smears on symptomatic patients. We estimated: (i) the number of malaria cases detected by the PACD, divided by the total number of reported malaria cases during the same period among the same population; (ii) the time between onset of symptoms, diagnosis and initiation of treatment. The total number of migrants who were screened for malaria symptoms for the years 2012–2017 was 5057 with 84,169 fever screenings conducted, while 2288 RDTs and 1736 blood smears were performed. During the same period, 53 imported P. vivax malaria cases were detected, while incidence of malaria among migrants was estimated at 1.8% annually. Ten and one LAM cases were also reported in 2012 and 2015, respectively. Sensitivity of PACD ranged from 86% to 100%; median timeliness between onset of symptoms and diagnosis decreased from 72 h in 2012 to 12 h in 2017 (83% decrease), while timeliness between diagnosis and treatment initiation was 0 h. The implementation of PACD could be considered an effective prevention and response tool against malaria re-introduction.

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

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.

Population Genetics and Molecular Epidemiology of Eukaryotes

Molecular epidemiology uses the distribution and organization of a pathogen's DNA to understand the distribution and determinants of disease. Since the biology of DNA for eukaryotic pathogens differs substantially from that of bacteria, the analytic approach to their molecular epidemiology can also differ. While many of the genotyping techniques presented earlier in this series, "Advances in Molecular Epidemiology of Infectious Diseases," can be applied to eukaryotes, the output must be interpreted in the light of how DNA is distributed from one generation to the next. In some cases, parasite populations can be evaluated in ways reminiscent of bacteria. They differ, however, when analyzed as sexually reproducing organisms, where all individuals are unique but the genetic composition of the population does not change unless a limited set of events occurs. It is these events (migration, mutation, nonrandom mating, selection, and genetic drift) that are of interest. At a given time, not all of them are likely to be equally important, so the list can easily be narrowed down to understand the driving forces behind the population as it is now and even what it will look like in the future. The main population characteristics measured to assess these events are differentiation and diversity, interpreted in the light of what is known about the population from observation. The population genetics of eukaryotes is important for planning and evaluation of control measures, surveillance, outbreak investigation, and monitoring of the development and spread of drug resistance. *This article is part of a curated collection.

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

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.

Concurrent Autochthonous Malaria Caused by Plasmodium vivax in Father and Son in Greece

We report the case of a 12-year-old child who was admitted to our Department, with 7 days' history of high fever and splenomegaly. His father had similar symptoms starting on the same day. A rapid test and microscopy for malaria yielded a positive result for Plasmodium vivax Antimalarial therapy was initiated. He developed methemoglobinemia treated with ascorbic acid and had uneventful recovery.

Malaria in Europe: emerging threat or minor nuisance?

Malaria was eradicated from Europe in the 1970s through a combination of insecticide spraying, drug therapy and environmental engineering. Since then, it has been mostly imported into the continent by international travellers and immigrants from endemic regions. Despite the substantial number of imported malaria cases and the documented presence of suitable anopheline vectors, autochthonous transmission has not been widely observed in Europe, probably as a result of early diagnosis and treatment, afforded by efficient healthcare systems. Current climatic conditions are conducive to malaria transmission in several areas of Southern Europe, and climate change might favour mosquito proliferation and parasite development, further facilitating malaria transmission. Moreover, the continuing massive influx of refugee and migrant populations from endemic areas could contribute to building up of an infectious parasite reservoir. Although the malariogenic potential of Europe is currently low, particularly in the northern and western parts of the continent, strengthening of disease awareness and maintaining robust public health infrastructures for surveillance and vector control are of the utmost importance and should be technically and financially supported to avert the possibility of malaria transmission in Europe's most vulnerable areas.

Neglected Plasmodium vivax malaria in northeastern States of India

BACKGROUND & OBJECTIVES

The northeastern States of India are co-endemic for Plasmodium falciparum and P. vivax malaria. The transmission intensity is low-to-moderate resulting in intermediate to stable malaria. Malaria control prioritized P. falciparum being the predominant and life threatening infection (>70%). P. vivax malaria remained somewhat neglected. The present study provides a status report of P. vivax malaria in the northeastern States of India.

METHODS

Data on spatial distribution of P. vivax from seven northeastern States (Arunachal Pradesh, Assam, Manipur, Meghalaya, Mizoram, Nagaland and Tripura) were analysed retrospectively from 2008-2013. In addition, cross-sectional malarial surveys were conducted during 1991-2012 in malaria endemic pockets across the States of Assam, Meghalaya, Mizoram and Tripura to ascertain the prevalence of P. vivax in different age groups.

RESULTS

Vivax malaria was encountered in all northeastern States but there existed a clear division of two malaria ecotypes supporting ≤30 and >30 per cent of total malaria cases. High proportions of P. vivax cases (60-80%) were seen in Arunachal Pradesh and Nagaland in the north with alpine environment, 42-67 per cent in Manipur, whereas in Assam it varied from 23-31 per cent with subtropical and tropical climate. Meghalaya, Tripura and Mizoram had the lowest proportion of P. vivax cases. Malaria cases were recorded in all age groups but a higher proportion of P. vivax consistently occurred among <5 yr age group compared to P. falciparum (P<0.05). P. vivax cases were recorded throughout the year with peak coinciding with rainy season although transmission intensity and duration varied.

INTERPRETATION & CONCLUSIONS

In northeast India, P. vivax is a neglected infection. Estimating the relapsing pattern and transmission dynamics of P. vivax in various ecological settings is an important pre-requisite for planning malaria elimination in the northeastern States.

Prevention of Malaria Resurgence in Greece through the Association of Mass Drug Administration (MDA) to Immigrants from Malaria-Endemic Regions and Standard Control Measures

Greece was declared malaria-free in 1974 after a long antimalarial fight. In 2011–2012, an outbreak of P. vivax malaria was reported in Evrotas, an agricultural area in Southern Greece, where a large number of immigrants from endemic countries live and work. A total of 46 locally acquired and 38 imported malaria cases were detected. Despite a significant decrease of the number of malaria cases in 2012, a mass drug administration (MDA) program was considered as an additional measure to prevent reestablishment of the disease in the area. During 2013 and 2014, a combination of 3-day chloroquine and 14-day primaquine treatment was administered under direct observation to immigrants living in the epicenter of the 2011 outbreak in Evrotas. Adverse events were managed and recorded on a daily basis. The control measures implemented since 2011 continued during the period of 2013–2014 as a part of a national integrated malaria control program that included active case detection (ACD), vector control measures and community education. The MDA program was started prior to the transmission periods (from May to December). One thousand ninety four (1094) immigrants successfully completed the treatment, corresponding to 87.3% coverage of the target population. A total of 688 adverse events were recorded in 397 (36.2%, 95% C.I.: 33.4–39.1) persons, the vast majority minor, predominantly dizziness and headache for chloroquine (284 events) and abdominal pain (85 events) for primaquine. A single case of primaquine-induced hemolysis was recorded in a person whose initial G6PD test proved incorrect. No malaria cases were recorded in Evrotas, Laconia, in 2013 and 2014, though three locally acquired malaria cases were recorded in other regions of Greece in 2013. Preventive antimalarial MDA to a high-risk population in a low transmission setting appears to have synergized with the usual antimalarial activities to achieve malaria elimination. This study suggests that judicious use of MDA can be a useful addition to the antimalarial armamentarium in areas threatened with the reintroduction of the disease.

Greece was declared malaria-free in the year 1974 after a long antimalarial fight. In 2011–2012, a number of malaria cases reported in Evrotas, Laconia, in Southern Greece, where a large number of immigrants from malaria-endemic countries live and work. A total of 84 malaria cases, both in immigrants (38 cases) and in Greeks (46 cases), were detected. A number of malaria control measures were deployed in the area since 2011. Despite a decrease of the number of malaria cases in 2012, elimination could not be achieved, and thus antimalarial MDA was considered as an additional measure to prevent the reestablishment of the disease. During 2013 and 2014, a combination of two drugs was administered under direct observation to all immigrants in the epicenter of the 2011 Evrotas outbreak. The antimalarial MDA program was started on July-August and was successfully completed by 1094 immigrants (87.3% coverage). No serious adverse events were recorded except one case of primaquine-induced hemolysis due to false G6PD test result. In 2013 and 2014, no malaria cases were recorded in Evrotas, Laconia. This study suggests that careful use of supervised antimalarial MDA is a useful addition to the antimalarial control measures in areas threatened with the reintroduction of the disease.

Malaria knowledge, attitudes and practices among migrants from malaria-endemic countries in Evrotas, Laconia, Greece, 2013

Following re-emergence of malaria in Evrotas, Laconia, in 2009–12, a malaria-control programme was implemented in 2011–12 targeting migrants from malaria-endemic countries, including house-to-house active case detection, health education and distribution of mosquito protection items. In June 2013, we surveyed migrants in Evrotas to assess their malaria knowledge, attitudes and practices to guide prevention activities. We selected participants using simple random sampling and interviewed them, using structured questionnaires. We defined mosquito protection practices (MPPs) as the use of full-length clothes/topical repellent, mosquito screens, fans or air-conditioning, and insecticides. We calculated prevalence ratios (PRs) using Poisson regression and we allowed for clustering of participants in a residence. Of 654 migrants, we invited 132 and 130 participated (all men; 120 (92%) from Pakistan). Of the 130, 56 (43%) identified fever as a malaria symptom; those who were aware of this had higher level of education (PR: 3.2; 95% confidence interval (CI): 1.2–9.0). A total of 111 (85%) used insecticide-treated bednets and 95 (73%) used more than two MPPs. Poor housing conditions (warehouses/shacks: PR: 0.8; 95% CI: 0.6–0.9), were associated with use of up to two MPPs. Despite extensive interventions in Evrotas, the level of malaria awareness among migrants remained suboptimal and poor housing conditions hindered effective mosquito protection. We recommend culturally adapted health education and improvement of housing conditions to minimise the risk of new cases and re-establishment of malaria in Greece.

Uncovering the transmission dynamics of Plasmodium vivax using population genetics

Population genetic analysis of malaria parasites has the power to reveal key insights into malaria epidemiology and transmission dynamics with the potential to deliver tools to support control and elimination efforts. Analyses of parasite genetic diversity have suggested that Plasmodium vivax populations are more genetically diverse and less structured than those of Plasmodium falciparum indicating that P. vivax may be a more ancient parasite of humans and/or less susceptible to population bottlenecks, as well as more efficient at disseminating its genes. These population genetic insights into P. vivax transmission dynamics provide an explanation for its relative resilience to control efforts. Here, we describe current knowledge on P. vivax population genetic structure, its relevance to understanding transmission patterns and relapse and how this information can inform malaria control and elimination programmes.

Plasmodium vivax populations are more genetically diverse and less structured than sympatric Plasmodium falciparum populations

Introduction

The human malaria parasite, Plasmodium vivax, is proving more difficult to control and eliminate than Plasmodium falciparum in areas of co-transmission. Comparisons of the genetic structure of sympatric parasite populations may provide insight into the mechanisms underlying the resilience of P. vivax and can help guide malaria control programs.

Methodology/Principle findings

P. vivax isolates representing the parasite populations of four areas on the north coast of Papua New Guinea (PNG) were genotyped using microsatellite markers and compared with previously published microsatellite data from sympatric P. falciparum isolates. The genetic diversity of P. vivax (H_e = 0.83–0.85) was higher than that of P. falciparum (H_e = 0.64–0.77) in all four populations. Moderate levels of genetic differentiation were found between P. falciparum populations, even over relatively short distances (less than 50 km), with 21–28% private alleles and clear geospatial genetic clustering. Conversely, very low population differentiation was found between P. vivax catchments, with less than 5% private alleles and no genetic clustering observed. In addition, the effective population size of P. vivax (30353; 13043–69142) was larger than that of P. falciparum (18871; 8109–42986).

Conclusions/Significance

Despite comparably high prevalence, P. vivax had higher diversity and a panmictic population structure compared to sympatric P. falciparum populations, which were fragmented into subpopulations. The results suggest that in comparison to P. falciparum, P. vivax has had a long-term large effective population size, consistent with more intense and stable transmission, and limited impact of past control and elimination efforts. This underlines suggestions that more intensive and sustained interventions will be needed to control and eventually eliminate P. vivax. This research clearly demonstrates how population genetic analyses can reveal deeper insight into transmission patterns than traditional surveillance methods.

The neglected human malaria parasite Plasmodium vivax is responsible for a large proportion of the global malaria burden. Efforts to control malaria have revealed that P. vivax is more resilient than the other major human malaria parasite, Plasmodium falciparum. This study utilised population genetics to compare patterns of P. vivax and P. falciparum transmission in Papua New Guinea, a region where infection rates of the two species are similar. The results demonstrated that P. vivax populations are more genetically diverse than those of P. falciparum suggestive of a parasite population that is more resilient to environmental challenges, undergoing higher levels of interbreeding locally and between distant parasite populations. Unique characteristics of P. vivax such as relapse, which allows different strains from past infections to produce subsequent infections, may provide more opportunities for the exchange and dissemination of genetic material. The contrasting patterns observed for the two species may be the result of a differential impact of past elimination attempts and indicate that more rigorous interventions will be needed in efforts to control and eventually eliminate P. vivax.

Tracking malaria parasites in the eradication era

As more endemic countries enter the elimination phase, the detection of sporadic malaria infections or outbreaks elicits many questions: (i) are the infections locally acquired or imported? (ii) If imported, where do they come from? (iii) Do outbreak strains have a single or multiple geographic origins? New molecular barcoding methods provide ways to analyze clinical malaria parasite samples and answer these and other crucial questions.