Malaria in Eritrean migrants newly arrived in seven European countries, 2011 to 2016

Scoring systems for prediction of malaria and dengue fever in non-endemic areas among travellers arriving from tropical and subtropical areas

BACKGROUND

Fever is a common symptom among travellers returning from tropical/subtropical areas to Europe, and promptly distinguishing severe illnesses from self-limiting febrile syndromes is important but can be challenging due to non-specific clinical presentation.

METHODS

A cross-sectional study enrolled adults and children who sought care during 2015-2020 at Karolinska University Hospital, Stockholm, Sweden with fever within 2 months after returning from travel to a tropical/subtropical area. Data on symptoms and laboratory parameters were prospectively and retrospectively collected. Two separate scoring systems for malaria and dengue were developed based on backward elimination regressions.

RESULTS

In total, 2113 adults (18-94 years) and 202 children (1-17 years) were included, with 112 (4.8%) confirmed malaria by blood thick smear and 90 (3.9%) PCR/serology dengue-positive cases. Malaria was more likely in a patient who had visited sub-Saharan Africa and presented with combination of thrombocytopenia, anaemia and fever ≥39.5°C. Leucopenia, muscle pain and rash after travelling to Asia or South/Latin America indicated high probability of dengue. Two scoring systems with points between 0 and 7 for prediction of malaria or dengue were created based on the above predictors. Scores ≥3 indicated >80% sensitivity and specificity for malaria and >90% specificity for dengue in children and adults (area under the curve (AUC) for dengue: 0.92 in adults (95% CI 0.90 to 0.95) and 0.95 in children (95% CI 0.88 to 1.0); AUC for malaria: 0.93 in adults (95% CI 0.91 to 0.96) and 0.88 in children (95% CI 0.78 to 0.99)). Internal validation of optimism and overfitting was managed with bootstrap.

CONCLUSION

The presented scoring systems provide novel tools for structured assessment of patients with tropical fever in a non-endemic area and highlight clinical signs associated with a potential severe aetiology to direct the need for microbial investigation.

Malaria parasite prevalence among migrants: a systematic review and meta-analysis

BACKGROUND

Asymptomatic malaria infections are highly prevalent in endemic areas.

OBJECTIVES

This systematic review aimed to estimate the pooled prevalence of malaria parasites in migrants screened in non-endemic areas.

DATA SOURCES

MEDLINE-Ovid, EMBASE, Web of Science, Global Health, Lilacs, Cochrane, and MedRxiv.

STUDY ELIGIBILITY CRITERIA

Cross-sectional studies and observational prospective or retrospective cohort studies conducted in Europe, USA, Canada, Australia, or New Zealand regardless of language or publication status. Studies should include prevalence data on malaria in migrants that were recruited through a systematic screening approach. We excluded studies where people were tested because of malaria symptoms.

PARTICIPANTS

Migrant individuals exposed to malaria infection ASSESSMENT OF RISK OF BIAS: A standardized and validated appraisal instrument was used for studies reporting prevalence data (Joanna Briggs Institute Manual for Evidence Synthesis).

METHODS OF DATA SYNTHESIS

Pooled estimates of the parasite prevalence by PCR, microscopy, and rapid diagnostic test (RDT) were calculated with a random-effects model. Heterogeneity was explored by stratification by age, region of origin, period of study, and quality of studies.

RESULTS

Of 1819 studies retrieved, 23 studies were included with in total 4203 participant PCR data, 3186 microscopy and 4698 RDT data, respectively. Migrants from sub-Saharan Africa had a malaria parasite prevalence of 8.3% (95% CI 5.1-12.2) by PCR, 4.3% (1.5-8.2) by RDT, and 3.1% (0.7-6.8) by microscopy. For migrants from Asia and Latin America, the prevalence with PCR was 0% (0.0-0.08) and 0.4% (0.0-1.8), respectively. Migrants from the Central African Region had the highest PCR prevalence (9.3% [6.0-13.0]), followed by West African migrants (2.0% [0.0-7.7]). Restricting the analysis to sub-Saharan Africa migrants arriving to the host country within the previous year, the PCR-based prevalence was 11.6% (6.9-17.4).

CONCLUSION

We provide estimates on the malaria parasite prevalence in migrants in non-endemic setting. Despite heterogeneity between settings, these findings can contribute to inform screening strategies and guidelines targeting malaria in migrants.

Malaria parasite prevalence in Sub-Saharan African migrants screened in Sweden: a cross-sectional study

Background

Asymptomatic infections with malaria parasites are common in populations in endemic areas. These infections may persist in migrants after arrival in a non-endemic area. Screening to find and clear these infections is generally not implemented in non-endemic countries, despite a potential negative health impact. We performed a study to evaluate the Plasmodium parasite prevalence in migrants living in Sweden.

Methods

Adults and children born in Sub-Saharan Africa (SSA) were invited in the study between April 2019 and June 2022 at 10 different sites, mainly as part of the national Migrant Health Assessment Program in Stockholm and Västerås, Sweden. Rapid diagnostic tests (RDT) and real-time PCR were used to detect malaria parasites. Prevalence and test sensitivity were calculated with 95% confidence intervals (CI). Univariate and multivariable logistic regression were used to evaluate associations with PCR positivity.

Findings

In total, 789 individuals were screened for Plasmodium spp. of which 71 (9.0%) were positive by PCR and 18 (2.3%) also by RDT. When performed during the national screening program, 10.4% was PCR positive. A high prevalence was detected in migrants with Uganda as the country of last residence, 53/187 (28.3%), and in this group the prevalence was highest in children, 29/81 (35.8%). Among the PCR positive, 47/71 (66.2%) belonged to families with at least one other member testing positive (odds ratio [OR] 43.4 (95% CI 19.0-98.9), and the time lived in Sweden ranged between 6 and 386 days.

Interpretation

A high malaria parasite prevalence was found in migrants from SSA, particularly in children offered screening in Stockholm, Sweden during the study period. Awareness of asymptomatic malaria infection is needed and screening for malaria in migrants arriving from high endemic countries should be considered.

Funding

The Swedish Research Council, Stockholm County Council and Centre for Clinical Research, Västmanland, Sweden.

Relapse of Plasmodium vivax and Plasmodium ovale malaria with and without primaquine treatment in a non-endemic area

Background

The effect of primaquine in preventing Plasmodium vivax relapses from dormant stages is well established. For Plasmodium ovale, the relapse characteristics and the use of primaquine is not as well studied. We set to evaluate the relapsing properties of these 2 species, in relation to primaquine use among imported malaria cases in a nonendemic setting.

Methods

We performed a nationwide retrospective study of malaria diagnosed in Sweden 1995–2019, by reviewing medical records of 3254 cases. All episodes of P. vivax (n = 972) and P. ovale (n = 251) were selected for analysis.

Results

First time relapses were reported in 80/857 (9.3%) P. vivax and 9/220 (4.1%) P. ovale episodes, respectively (P < .01). Without primaquine, the risk for relapse was higher in P. vivax, 20/60 (33.3%), compared to 3/30 (10.0%) in P. ovale (hazard ratio [HR] 3.5, 95% confidence interval [CI] 1.0–12.0). In P. vivax, patients prescribed primaquine had a reduced risk of relapse compared to episodes without relapse preventing treatment, 7.1% vs 33.3% (HR 0.2, 95% CI .1–.3). In P. ovale, the effect of primaquine on the risk of relapse did not reach statistical significance, with relapses seen in 2.8% of the episodes compared to 10.0% in patients not receiving relapse preventing treatment (HR 0.3, 95% CI .1–1.1).

Conclusions

The risk of relapse was considerably lower in P. ovale than in P. vivax infections indicating different relapsing features between the two species. Primaquine was effective in preventing P. vivax relapse. In P. ovale, relapse episodes were few, and the supportive evidence for primaquine remains limited.

The Pan African Vivax and Ovale Network (PAVON): Refocusing on Plasmodium vivax, ovale and asymptomatic malaria in sub-Saharan Africa

The recent World Malaria report shows that progress in malaria elimination has stalled. Current data acquisition by NMCPs depend on passive case detection and clinical reports focused mainly on Plasmodium falciparum (Pf). In recent times, several countries in sub-Saharan Africa have reported cases of Plasmodium vivax (Pv) with a considerable number being Duffy negative. The burden of Pv and Plasmodium ovale (Po) appear to be more than acknowledged. Similarly, the contribution of asymptomatic malaria in transmission is hardly considered by NMCPs in Africa. Inclusion of these as targets in malaria elimination agenda is necessary to achieve elimination goal, as these harbor hypnozoites. The Pan African Vivax and Ovale Network (PAVON) is a new consortium of African Scientists working in Africa on the transmission profile of Pv and Po. The group collaborates with African NMCPs to train in Plasmodium molecular diagnostics, microscopy, and interpretation of molecular data from active surveys to translate into policy. Details of the mission, rational and modus operandi of the group are outlined.

The spatiotemporal distribution of historical malaria cases in Sweden: a climatic perspective

Background

Understanding of the impacts of climatic variability on human health remains poor despite a possibly increasing burden of vector-borne diseases under global warming. Numerous socioeconomic variables make such studies challenging during the modern period while studies of climate–disease relationships in historical times are constrained by a lack of long datasets. Previous studies have identified the occurrence of malaria vectors, and their dependence on climate variables, during historical times in northern Europe. Yet, malaria in Sweden in relation to climate variables is understudied and relationships have never been rigorously statistically established. This study seeks to examine the relationship between malaria and climate fluctuations, and to characterise the spatio-temporal variations at parish level during severe malaria years in Sweden 1749–1859.

Methods

Symptom-based annual malaria case/death data were obtained from nationwide parish records and military hospital records in Stockholm. Pearson (r_p) and Spearman’s rank (r_s) correlation analyses were conducted to evaluate inter-annual relationship between malaria data and long meteorological series. The climate response to larger malaria events was further explored by Superposed Epoch Analysis, and through Geographic Information Systems analysis to map spatial variations of malaria deaths.

Results

The number of malaria deaths showed the most significant positive relationship with warm-season temperature of the preceding year. The strongest correlation was found between malaria deaths and the mean temperature of the preceding June–August (r_s = 0.57, p < 0.01) during the 1756–1820 period. Only non-linear patterns can be found in response to precipitation variations. Most malaria hot-spots, during severe malaria years, concentrated in areas around big inland lakes and southern-most Sweden.

Conclusions

Unusually warm and/or dry summers appear to have contributed to malaria epidemics due to both indoor winter transmission and the evidenced long incubation and relapse time of P. vivax, but the results also highlight the difficulties in modelling climate–malaria associations. The inter-annual spatial variation of malaria hot-spots further shows that malaria outbreaks were more pronounced in the southern-most region of Sweden in the first half of the nineteenth century compared to the second half of the eighteenth century.