Distribution of Plasmodium spp. infection in asymptomatic carriers in perennial and low seasonal malaria transmission settings in West Africa

Abstract

BackgroundSince 2000, substantial progress has been made in reducing malaria worldwide. However, some countries in West Africa remain a hotspot for malaria with all age groups at risk. Asymptomatic carriers of Plasmodium spp. are important sources of infections for malaria vectors and thus contribute to the anchoring of the disease in favourable eco-epidemiological settings. The objective of this study was to assess the asymptomatic malaria case rates in Korhogo and Kaedi, two urban areas in northern Côte d’Ivoire and southern Mauritania, respectively.MethodsCross-sectional surveys were carried out during the rainy season in 2014 and the dry season in 2015 in both settings. During each season, 728 households were randomly selected and a household-based questionnaire was implemented to collect demographic and epidemiological data, including of malaria preventive methods used in communities. Finger-prick blood samples were obtained for biological examination using microscopy and rapid diagnostic tests (RDTs).ResultsOverall, 2672 households and 15 858 consenting participants were surveyed. Plasmodium spp. infection was confirmed in 12.4% (n = 832) and 0.3% (n = 22) of the assessed individuals in Korhogo and Kaedi, respectively. In Korhogo, the prevalence of asymptomatic malaria was 10.5% (95% CI: 9.7–11.2) as determined by microscopy and 9.3% (95% CI: 8.6–10.0%) when assessed by RDT. In Kaedi, asymptomatic malaria prevalence was 0.2% (95% CI: 0.1–0.4%) according to microscopy, while all RDTs performed were negative (n = 8372). In Korhogo, asymptomatic malaria infection was significantly associated with age and season, with higher risk within the 5–14 years-old, and during the rainy season. In Kaedi, the risk of asymptomatic malaria infection was associated with season only (higher during the dry season; crude OR (cOR): 6.37, 95% CI: 1.87–21.63). P. falciparum was the predominant species identified in both study sites representing 99.2% (n = 825) in Korhogo and 59.1% (n = 13) in Kaedi. Gametocytes were observed only in Korhogo and only during the rainy season at 1.3% (95% CI: 0.7–2.4%).ConclusionsOur findings show a low prevalence of clinical malaria episodes with a significant proportion of asymptomatic carriers in both urban areas. National policies for malaria infections are focused on treatment of symptomatic cases. Malaria control strategies should be designed for monitoring and managing malaria infections in asymptomatic carriers. Additional measures, including indoor residual spraying, effective use of long-lasting insecticidal nets is strongly needed to reduce the number of Plasmodium spp. infections in Korhogo and Kaedi.Electronic supplementary materialThe online version of this article (10.1186/s40249-018-0412-9) contains supplementary material, which is available to authorized users.

Prevalence of asymptomatic malaria infections in selected military camps in Tanzania

“…Periodic monitoring to identify pocket areas for P. falciparum infections is vital for malaria elimination efforts. Since good proportion of P. falciparum infections are asymptomatic in most endemic countries (Males et al, 2008;Singh et al, 2014), they are responsible for maintaining parasite transmission cycle in presence of mosquitoes vectors (Gbalégba et al, 2018;Kimbi, 2012;Mehrizi et al, 2012). In Tanzania, there are some areas including military setting where malaria incidence rates are still high despite recent reported fall in morbidity and mortality rates.…”

Diversity and Multiplicity of P. falciparum infections among asymptomatic school children in Mbita, Western Kenya

“…The stagnancy in the global fight against the disease is partly due to decreased funding from international donors 1,[20][21][22][23] . However, the high prevalence of asymptomatic carriers especially among older children 19,[24][25][26][27][28] , high recombination rates among distinct P. falciparum clones in endemic settings leading to emergence of highly diverse parasite isolates, rapid emergence and distribution of drug resistant P. falciparum parasite strains [29][30][31][32][33] , and prevalence of infections characterized by multiple genetically distinct parasite strains are some of the major contributing factors hindering the global malaria control and elimination 31,34,35 . In highly endemic environments, many individuals carry multiple parasite clones [36][37][38] .…”

Towards the Use of a Smartphone Imaging-Based Tool for Point-of-Care Detection of Asymptomatic Low-Density Malaria Parasitemia

“…(7-9) Asymptomatic carriers of P. falciparum malaria are largely responsible for persistent transmission by maintaining the parasite life cycle. (8,10,11) Malaria management strategies are needed to control and monitor infections in asymptomatic carriers and are a key step towards elimination. (10) Rapid and sensitive asymptomatic malaria detection would provide real-time disease surveillance for disease outbreak identification and prevent further transmission.…”

“…(8,10,11) Malaria management strategies are needed to control and monitor infections in asymptomatic carriers and are a key step towards elimination. (10) Rapid and sensitive asymptomatic malaria detection would provide real-time disease surveillance for disease outbreak identification and prevent further transmission. However, current on-site malaria detection approaches often rely on diagnostics that are not sensitive enough for asymptomatic malaria cases.…”