Abstract
BackgroundSubmicroscopic Plasmodium falciparum infections are widespread in many areas. However, the contribution of these infections to symptomatic malaria is not well understood. This study evaluated whether participants with submicroscopic P. falciparum infections have higher prevalence of fever than uninfected participants in southern Malawi.MethodsA total of 16,650 children and adults were enrolled in the course of six cross-sectional surveys during the dry season (October–November) and after the rainy season (April–May) between 2012 and 2014 in three districts in southern Malawi. Demographic and socioeconomic data were collected in conjunction with data on clinical histories, use of malaria preventive measures, and anti-malarial medication taken within 2 weeks of the survey. Axillary temperatures were measured, and blood samples were collected for P. falciparum detection by microscopy and PCR. Participants without malaria parasites detected on microscopy but with a positive PCR for P. falciparum were defined as having submicroscopic infection. Fever was defined as having any one of: reported fever in the past 2 weeks, reported fever in the past 48 h, or a temperature of ≥ 37.5 °C measured at the time of interview.ResultsSubmicroscopic P. falciparum infections and fever were both detected in 9% of the study population. In the final analysis adjusted for clustering within household and enumeration area, having submicroscopic P. falciparum infection was associated with reduced odds of fever in the dry season (odds ratio = 0.52; 95% CI 0.33–0.82); the association in the rainy season did not achieve statistical significance (odds ratio = 1.20; 95% CI 0.91–1.59). The association between submicroscopic infection and fever was consistent across all age groups. When the definition of fever was limited to temperature of ≥ 37.5 °C measured at the time of interview, the association was not statistically significant in either the rainy or dry season.ConclusionsIn this series of cross-sectional studies in southern Malawi, submicroscopic P. falciparum infection was not associated with increased risk of fever. Submicroscopic detection of the malaria parasite is important in efforts to decrease transmission but is not essential for the clinical recognition of malaria disease.
Highlights
Submicroscopic Plasmodium falciparum infections are widespread in many areas
Accurate estimation of the incidence and prevalence of P. falciparum infections in many geographical areas has been difficult because microscopy, the gold standard for the clinical diagnosis of malaria illnesses, and rapid diagnostic tests (RDTs) are not sensitive enough to detect low-density parasitaemia [12, 13]
The distribution of participants within sex, age groups, and seasonal categories was similar in the three districts (Table 1)
Summary
Submicroscopic Plasmodium falciparum infections are widespread in many areas. the contribution of these infections to symptomatic malaria is not well understood. Vareta et al Malar J (2020) 19:233 illnesses with artemisinin-based combination therapy is increasing, and measures to reduce the transmission of malaria parasites (e.g., indoor residual spraying and longlasting insecticide-treated bed nets) are being widely used in many malaria-endemic areas [2, 3], there is growing evidence that low-density Plasmodium falciparum infections remain widespread [4,5,6,7,8]. These low-density P. falciparum infections act as transmission reservoir of malaria [9,10,11], their contribution to symptomatic malaria is not well understood. The goal of this study was to elucidate the clinical impact of submicroscopic malaria infections detected only by sensitive molecular techniques such as PCR [16, 17]
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