Abstract
BackgroundThe importance of submicroscopic malaria infections in high-transmission areas could contribute to maintain the parasite cycle. Regarding non-endemic areas, its importance remains barely understood because parasitaemia in these afebrile patients is usually below the detection limits for microscopy, hence molecular techniques are often needed for its diagnosis. In addition to this, the lack of standardized protocols for the screening of submicroscopic malaria in immigrants from endemic areas may underestimate the infection with Plasmodium spp. The aim of this study was to assess the prevalence of submicroscopic malaria in afebrile immigrants living in a non-endemic area.MethodsA prospective, observational, multicentre study was conducted. Afebrile immigrants were included, microscopic observation of Giemsa-stained thin and thick blood smears, and two different molecular techniques detecting Plasmodium spp. were performed. Patients with submicroscopic malaria were defined as patients with negative blood smears and detection of DNA of Plasmodium spp. with one or both molecular techniques. Demographic, clinical, analytical and microbiological features were recorded and univariate analysis by subgroups was carried out with STATA v15.ResultsA total of 244 afebrile immigrants were included in the study. Of them, 14 had a submicroscopic malaria infection, yielding a prevalence of 5.7% (95% confidence interval 3.45–9.40). In 71.4% of the positive PCR/negative microscopy cases, Plasmodium falciparum alone was the main detected species (10 out of the 14 patients) and in 4 cases (28.6%) Plasmodium vivax or Plasmodium ovale were detected. One patient had a mixed infection including three different species.ConclusionsThe prevalence of submicroscopic malaria in afebrile immigrants was similar to that previously described in Spain. Plasmodium vivax and P. ovale were detected in almost a third of the submicroscopic infections. Screening protocols for afebrile immigrants with molecular techniques could be useful for a proper management of these patients.
Highlights
The importance of submicroscopic malaria infections in high-transmission areas could contribute to maintain the parasite cycle
Outside endemic areas, imported clinical malaria is a well-known disease; in 2017 more than 8000 imported malaria cases were reported in immigrants and travellers in European Union countries [3], of which 748 occurred in Spain [4]
All samples were sent to the Microbiology Service of Hospital Universitario 12 de Octubre where thick and thin smears were observed by the same microscopist for all samples and a commercial real-time polymerase chain reaction (PCR) (FTD-Malaria, Fast-Track Diagnostics) detecting Plasmodium spp. was performed
Summary
The importance of submicroscopic malaria infections in high-transmission areas could contribute to maintain the parasite cycle. Outside endemic areas, imported clinical malaria is a well-known disease; in 2017 more than 8000 imported malaria cases were reported in immigrants and travellers in European Union countries [3], of which 748 occurred in Spain [4] In this regard, immigrants, including newly arrived immigrants and immigrants visiting friends and relatives (VFRs), account for most of the imported malaria cases in developed countries [5]. Immigrants, including newly arrived immigrants and immigrants visiting friends and relatives (VFRs), account for most of the imported malaria cases in developed countries [5] They often have milder symptoms and lower parasite loads than recently arrived travellers due to their semi-immunity. While management of clinical malaria is well-established in protocols in several developed countries [8, 9], submicroscopic infections are not usually discussed
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