Prevalence of asymptomatic malaria, submicroscopic parasitaemia and anaemia in Korogwe District, north-eastern Tanzania

Paul M Hayuma,Vito Baraka,Gerald Misinzo,Michael Alifrangis,Daniel T R Minja,John P A Lusingu,Christian W Wang,Rashid A Madebe,Edwin Liheluka

doi:10.1186/s12936-021-03952-3

Abstract

BackgroundAsymptomatic malaria infections largely remain undetected and act as a reservoir for continuous transmission. The study assessed the prevalence of submicroscopic asymptomatic malaria infections and anaemia in two rural low (300 m above sea level) and highland (700 m asl) settings of Korogwe District north-eastern Tanzania.MethodsA cross-sectional malariometric survey involving individuals aged 0–19 years was conducted in June 2018 in the two rural villages. Venous blood was collected from eligible study participants for estimation of haemoglobin level, detection of malaria by rapid diagnostic test (RDT), quantification of malaria parasitaemia by microscopy, as well as dried blood spot (DBS) for determining submicroscopic infections by PCR targeting the small subunit of the ribosomal ribonucleic acid (ssrRNA) of human Plasmodium.ResultsOut of 565 individuals tested, 211 (37.3%) were malaria positive based on RDT, whereas only 81 (14.3%) were positive by microscopy. There was no significant difference in the prevalence between the highland and the lowland village, p = 0.19 and p = 0.78 microscopy and RDT, respectively. Three out of 206 (1.5%) RDT/microscopy negative samples were P. falciparum positive by PCR. Of the 211 RDT and 81 microscopy positive, 130 (61.6%) and 33 (40.7%), respectively, were defined as being asymptomatic. Of the 565 individuals, 135 (23.9%) were anaemic (haemoglobin < 11 g/dL) out of which 5.2% were severely anaemic. The risk of being anaemic was significantly higher among individuals with asymptomatic malaria as compared to those without malaria as confirmed by RDT (AOR = 2.06 (95% CI 1.32–3.20) while based on microscopic results there was no significant differences observed (AOR = 2.09, 95% CI 0.98–4.47). Age and altitude had no effect on the risk of anaemia even after adjusting for asymptomatic malaria.ConclusionsAsymptomatic malaria is associated with an increased risk of having anaemia in the study communities. The findings highlight the need for targeted interventions focusing on asymptomatic infections which is an important risks factor for anaemia in the community and act as a source of continued transmission of malaria in the study area.

Highlights

Asymptomatic malaria infections largely remain undetected and act as a reservoir for continuous transmission
The present study revealed a high prevalence of asymptomatic malaria in this rural population of north-eastern Tanzania
It is high time that instead of focusing on underfive and pregnant women, targeted malaria control interventions consider school aged children who seem to be most vulnerable. Such a high proportion of asymptomatic malaria among those aged above 5 years suggests that school aged children are a major reservoir of malaria which is in line with other malaria studies from school aged children in Tanzania [18,19,20]. This raises an alarm for having targeted malaria control programmes for this particular group as these asymptomatic infections may result into persistently low level parasitaemia that may precipitate into anaemia and affect cognitive ability among school aged children

Summary

Introduction

Asymptomatic malaria infections largely remain undetected and act as a reservoir for continuous transmission. The study assessed the prevalence of submicroscopic asymptomatic malaria infections and anaemia in two rural low (300 m above sea level) and highland (700 m asl) settings of Korogwe District north-eastern Tanzania. In malarial endemic settings, repeated infections cause a partial non-sterilizing immunity to malaria resulting into asymptomatic and often, chronic infections that are rarely detected and may end up not being treated [8]. Many of these asymptomatic malaria carriers maintain low level parasitaemia and gametocytaemia which may play a significant role in transmission [9]. Even low level malaria parasitaemia is associated with an increased risk of anaemia [10, 11] and may impair cognitive development [12]

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Conclusion