Infections in Migrants in Sweden - the Importance of Malaria and Other Parasitic Infections
Conditions: Malaria, Parasitic Infection
Sponsor: Region Stockholm

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Study protocol  
 
Infections in migrants: the importance of malaria and other parasites  
 
 
2021-08-01 
 

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Study protocol  
 
Infections in migrants: the importance of malaria and other parasites 
 
Overall aim 
The purpose of this project is to improve the health in migrants and immigrants focusing on malaria 
and other parasitic infections. 
 
Specific aims 
1. 
To assess the parasite prevalence in newly arrived migrants and the need to introduce screening 
for malaria and other parasites in migrants from certain countries. 
2. 
To assess the parasite prevalence and specific antibody responses to malaria and other parasitic 
infections in immigrants who live in Sweden. 
 
Background 
Malaria is a major threat to human health, especially in Sub-Saharan Africa [1]. Global migration has 
resulted in a surge of refugees and asylum applications in Europe, many from malaria endemic 
countries.  
The symptoms of malaria range from mild febrile illness to life-threatening multi-organ failure [3]. 
Disease severity is influenced by several host-parasite interactions, where host immunity is believed 
to one of the most important [4].  
Immunity to malaria is gradually acquired after repeated infections in populations living in high-
endemic areas [4]. However, sterilizing immunity does not seem to evolve, and asymptomatic low-
level infections are common. Individuals may carry a low grade parasitemia for extended periods of 
time [5]. Chronic parasitemia may lead to anaemia [6], cognitive dysfunction [7], adverse events 
during pregnancy [8] and may have hidden cost on telomere degradation and ageing [9]. 
Migrants from malaria endemic areas may present with febrile malaria but may also harbour 
asymptomatic malaria infection. Moreover, other parasitic infection can cause silent infections with 
adverse effect on health, such as schistosomiasis causing bladder calcification and strongyloides that 
may progress to a life-threatening disease called strongyloides hyperinfection, especially in patients 
receiving corticosteroids or other immunomodulatory treatment.  
Thus, estimating the burden of malaria and other parasitic infections in newly arrived migrants as 
well as in immigrants with longer residency in Sweden is important in order to improve health in 
these populations.  
Previous studies have reported 3-30% parasite prevalence in asymptomatic refugees from malaria 
endemic areas [11-14]. In Sweden, health screening is offered to newly arrived immigrants, including 
HIV, tuberculosis and viral hepatitis. Currently, malaria is not included in the screening program in 

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Sweden, although other countries recommend screening [15-17] and in the US, presumptive 
treatment is offered without testing [18]. Neither is there any regular testing for other parasites, not 
even preceding long term corticosteroid treatment.   
Moreover, duration of asymptomatic parasite carriage in non-endemic countries is not fully 
established, however, case reports suggest that infections may persist for several years [20]. 
The immunologic response to malaria infection consists largely of antibodies towards a variety of 
parasite antigens, and develops over the course of several symptomatic malaria infections [22]. In 
highly endemic areas, immunity gradually protects against the severe forms of the disease and on 
further exposure, protection against clinical symptoms evolves [4, 22]. However, the protective 
immunity wanes over time with ceased exposure and thus previously protected individuals living in 
non-endemic countries are at risk for developing a more severe disease upon re-exposure for 
example when travelling to visit friends and relatives [23]. The longevity of circulating antibodies 
towards malaria is not fully elucidated, and therefore the risk cannot be fully appreciated.  
This project focuses on the burden of malaria and other parasitic infections in newly arrived migrants 
and immigrants with longer residency in Sweden. We will evaluate the parasite prevalence and if 
screening for malaria and other parasites should be offered in migrants from Sub-Saharan Africa. In 
addition, we will assess longevity of malaria-specific immune responses as well as how migrants 
navigate through the Swedish health system.  
 
 
Study design: Cross-sectional observational study. 
Study population:  
1. Newly arrived migrants born in countries where malaria is endemic (ie Sub-Saharan Africa) will be 
invited to participate in the study at migration health care units in Stockholm and Västerås. Blood 
samples will be collected at the time of routine sampling. According to sample size calculation 
based on expected 5% prevalence (see below) a total of 715 individuals will then be included in 
total. This number will be adjusted based on results in the pilot study. 
2. Immigrants from malaria endemic countries living in Sweden will be invited to participate with 
voluntary blood sampling on one occasion. The study will be advertised in posters in waiting areas 
at health clinics in Stockholm.  
3. Letter invitations to indivudials arriving in Sweden from Democratic Republic of the Congo and 
Uganda between 2015 and 2019 and with a postal address in the Stockholm County, will be sent 
an invitation letter offering to participate in the study. 
 
Inclusion criteria: Born in a malaria endemic country, defined as a country with indigenous spread of 
malaria reported in the World Malaria Report (WHO) 2019. 
Exclusion criteria: Inability to understand patient study information or inability sign the informed 
consent form, with exception to children under 15 where legal guardian may approve and sign 
consent.  
 

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Sampling and analyses: A venous blood samples (EDTA tube) will be collected on one occasion. To 
minimize the amount of venipunctures and time for the study participants, blood samples will be 
collected on the same occasion as other blood samples taken within the routine screening program 
for newly arrived migrants. A short questionnaire including questions about patient origin and 
previous malaria as well as other diseases and previous treatment will be completed at the time of 
sampling with the aid of a translator if needed. 
Blood samples will be sent to the research laboratory for malaria diagnostics and haemoglobin 
concentration. A rapid diagnostic test (RDT) will be performed for malaria. The sample will thereafter 
be centrifuged, aliquoted, and stored frozen at the research laboratory. Presence of parasites will be 
analysed by realtime-PCR of the species specific 18SRNA gene in a multiplex assay [25]. In study 
population 4, malaria microscopy will be performed at the same time as RDT to increase sensitivity. 
RDT is less sensitive than microscopy and PCR but offers a rapid result, the same day with this set up, 
and all positive individuals will be referred to the Department of Infectious Diseases at the regional 
hospital for further investigations and treatment. Likewise, all individuals found to be positive for 
malaria by microscopy and/or PCR at a later stage will be contacted and referred for complete 
assessment and treatment at the Department of Infectious Diseases. Results from complete blood 
count will be assessed and followed up according to clinical routine at each centre where samples 
were collected.  
Contact information to the study participant will be included as part of the recruitment and consent 
procedures in order to be able to contact the study participants for referral.  
Complementary to the proposed study, health economic aspects of malaria screening will be 
assessed for cost-effectiveness estimation.  
Moreover, PBMC will be prepared from a subset of patients to assess the cellular immune response. 
Plasma samples will be analyzed for the presence and levels of antibodies against crude whole P. 
falciparum parasite extract using ELISA, and against a panel of specific pre-hepatic and blood stage 
antigens using a multiplex Luminex [26]. The magnitude and breadth of antibody responses will be 
related to duration of residency in a malaria free country. This will allow us to estimate the long- 
term decay kinetics using a sero-epidemiological mathematical model [27]. In addition, serological 
markers for schistosomiasis and strongyloides will be analysed at the Public Health Agancy of 
Sweden. 
A subset of volunteers among immigrants living in Sweden (n=100) will be asked to contribute with a 
second blood sample after 6-12 months. This will allow us to estimate the long- term decay kinetics 
using a sero-epidemiological mathematical model [27].  
 
Statistical analysis 
The analyses will be performed using Stata version 14.2 (StataCorp, College Station, TX, USA). 
Categorical variables will be summarized by proportions, and the numerical variables by medians and 
interquartile ranges (IQR). In comparative analyses, categorical variables will be analyzed using the 
Pearson’s chi-squared test, or the Fisher's exact test when appropriate. The Mann-Whitney's U-test 
will be used for comparing the distribution of numeric variables between two groups and the 
Kruskal-Wallis's test among multiple groups. Backward stepwise univariable logistic regression will be 
used to potential risk factors for parasitic infection. The variables with a p-value less than 0.05 will be 

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kept in the final multivariable model. The Wald's test will be used to test the regression coefficients. 
P-values less than 0.05 were considered statistically significant. 
 
 
Significance 
Migration health and integration is of great concern and importance. The level of asymptomatic 
parasite carriage is unknown in migrants arriving to Sweden, however, chronic asymptomatic malaria 
may later on result in symptomatic disease or cause another burden on the host. Thus, the findings in 
this project have the potential to guide the prevention and management of malaria in migrants.   
Establishing the longevity and breadth of immune responses to malaria will contribute to vaccine 
design and will also help identification of populations at risk in areas of declining transmission and 
optimisation of sero-epidemiological models.  
Results from the questionnaire will be able to guide improved web-based information to immigrants 
about health care of febrile illness after tropical visits and in newly arrived migrants. The research 
and dissemination of results will improve the management of fever and malaria in high risk groups 
including children, adults and pregnant women originating from malaria endemic areas. 
 
Ethical considerations 
There are several ethical considerations in the proposed research project, related both to the study 
design and features of the study population. The study is performed on human volunteers after 
informed consent. However, migrants arriving in Sweden from malaria endemic countries come from 
diverse backgrounds and experiences of health care in their former home countries that could 
significantly differ from the organisation of the Swedish health care system. In this context, 
information about the project and how it is different from the offered health care (screening for 
other diseases) needs extra attention.  
We believe that bridging the cultural and language barriers will be possible with the aid of translators 
that are present during the health check-ups in the clinic. We have previously experienced that 
malaria is a well-known disease among individuals originating in malaria endemic areas and that it is 
not associated with any significant stigma, which will facilitate bilateral understanding.  
Furthermore, advantages of better malaria interventions justify blood sampling with only minor 
discomfort. The possible benefits of the study will favour future migrants from malaria endemic 
countries.  
 
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