Hyper-prevalence of submicroscopic Plasmodium falciparum infections in a rural area of western Kenya with declining malaria cases

Background The gold standard for diagnosing Plasmodium falciparum infection is microscopic examination of Giemsa-stained peripheral blood smears. The effectiveness of this procedure for infection surveillance and malaria control may be limited by a relatively high parasitaemia detection threshold. Persons with microscopically undetectable infections may go untreated, contributing to ongoing transmission to mosquito vectors. The purpose of this study was to determine the magnitude and determinants of undiagnosed submicroscopic P. falciparum infections in a rural area of western Kenya. Methods A health facility-based survey was conducted, and 367 patients seeking treatment for symptoms consistent with uncomplicated malaria in Homa Bay County were enrolled. The frequency of submicroscopic P. falciparum infection was measured by comparing the prevalence of infection based on light microscopic inspection of thick blood smears versus real-time polymerase chain reaction (RT-PCR) targeting P. falciparum 18S rRNA gene. Long-lasting insecticidal net (LLIN) use, participation in nocturnal outdoor activities, and gender were considered as potential determinants of submicroscopic infections. Results Microscopic inspection of blood smears was positive for asexual P. falciparum parasites in 14.7% (54/367) of cases. All of these samples were confirmed by RT-PCR. 35.8% (112/313) of blood smear negative cases were positive by RT-PCR, i.e., submicroscopic infection, resulting in an overall prevalence by RT-PCR alone of 45.2% compared to 14.7% for blood smear alone. Females had a higher prevalence of submicroscopic infections (35.6% or 72 out of 202 individuals, 95% CI 28.9–42.3) compared to males (24.2%, 40 of 165 individuals, 95% CI 17.6–30.8). The risk of submicroscopic infections in LLIN users was about half that of non-LLIN users (OR = 0.59). There was no difference in the prevalence of submicroscopic infections of study participants who were active in nocturnal outdoor activities versus those who were not active (OR = 0.91). Patients who participated in nocturnal outdoor activities and use LLINs while indoors had a slightly higher risk of submicroscopic infection than those who did not use LLINs (OR = 1.48). Conclusion Microscopic inspection of blood smears from persons with malaria symptoms for asexual stage P. falciparum should be supplemented by more sensitive diagnostic tests in order to reduce ongoing transmission of P. falciparum parasites to local mosquito vectors.

Meta-analysis of the prevalence of malaria associated with pregnancy in Colombia 2000–2020

Knowledge about malaria associated with pregnancy is scarce in Latin America, and in Colombia, little is known about the magnitude of this infection. A systematic review was conducted to determine the prevalence of malaria associated with pregnancy (MAP) and each of its three forms: gestational (GM), placental (PM), and congenital (CM) tested using thick blood smear (TBS) and PCR. Also to compare the proportion of cases due to Plasmodium falciparum and Plasmodium vivax in Colombia from the year 2000–2020. We searched in Pubmed, Science Direct, EMBASE, EMCare, Cochrane Library, Scielo, Lilacs, Google Scholar, libraries, and repositories of Colombian universities, to obtain data on prevalence of GM, PM and CM with their respective testing method. We performed a meta-analysis with a random-effects model to obtain pooled prevalence of MAP and its three forms categorized by testing methods (TBS and PCR). We used data from 14 studies (out of 258 screened) contributing 7932, 2506 women for GM and PM respectively, also data on 1143 umbilical cord blood samples, and 899 peripheral blood of neonates. We found prevalence by TBS as, MAP 4.5% (95%CI = 2.9–6.9), GM 5.8% (95%CI = 3.8–8.7), PM 3.4% (95%CI = 1.7–6.7) and CM 1.3% (95%CI = 0.6–3.0). With PCR the prevalence was, MAP 14.4% (95%CI = 7.6–25.5), GM 16.7% (95%CI = 9.0–28.8), PM 11.0% (95%CI = 4.1–26.3) and CM 16.2% (95%CI = 8.2–29.5). The prevalence of submicroscopic infection was 8.5% (95%CI = 3.4–19.7) in GM, 10.1% (95%CI = 3.5–25.5) in PM and 22.0% (95%CI = 13.2–34.3) in CM. Infections by P. vivax was dominant over P. falciparum when tested with TBS, the PCR test gave similar proportions of P. falciparum and P. vivax. This meta-analysis has demonstrated high prevalence of MAP in Colombia, and highlights the urgent need to increase attention of researchers, research funding institutions, government agencies, and health authorities to study and intervene MAP, that has currently been under investigated.

Reduced circulating dendritic cells in acute Plasmodium knowlesi and Plasmodium falciparum malaria despite elevated plasma Flt3 ligand levels

Background Plasmodium falciparum malaria increases plasma levels of the cytokine Fms-like tyrosine kinase 3 ligand (Flt3L), a haematopoietic factor associated with dendritic cell (DC) expansion. It is unknown if the zoonotic parasite Plasmodium knowlesi impacts Flt3L or DC in human malaria. This study investigated circulating DC and Flt3L associations in adult malaria and in submicroscopic experimental infection. Methods Plasma Flt3L concentration and blood CD141+ DC, CD1c+ DC and plasmacytoid DC (pDC) numbers were assessed in (i) volunteers experimentally infected with P. falciparum and in Malaysian patients with uncomplicated (ii) P. falciparum or (iii) P. knowlesi malaria. Results Plasmodium knowlesi caused a decline in all circulating DC subsets in adults with malaria. Plasma Flt3L was elevated in acute P. falciparum and P. knowlesi malaria with no increase in a subclinical experimental infection. Circulating CD141+ DCs, CD1c+ DCs and pDCs declined in all adults tested, for the first time extending the finding of DC subset decline in acute malaria to the zoonotic parasite P. knowlesi. Conclusions In adults, submicroscopic Plasmodium infection causes no change in plasma Flt3L but does reduce circulating DCs. Plasma Flt3L concentrations increase in acute malaria, yet this increase is insufficient to restore or expand circulating CD141+ DCs, CD1c+ DCs or pDCs. These data imply that haematopoietic factors, yet to be identified and not Flt3L, involved in the sensing/maintenance of circulating DC are impacted by malaria and a submicroscopic infection. The zoonotic P. knowlesi is similar to other Plasmodium spp in compromising DC in adult malaria.

Submicroscopic malaria infection is not associated with fever in cross-sectional studies in Malawi

Background: Submicroscopic Plasmodium falciparum infections are widespread in many areas. However, the contribution of these infections to symptomatic malaria is not well understood. In this study we evaluated whether participants with submicroscopic P. falciparum infections have higher prevalence of fever than uninfected participants in southern Malawi.Methods: We enrolled a total of 16,650 children and adults in the course of six cross-sectional surveys during the dry season (October - November) and after the rainy season (April - May) between 2012 - 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 antimalarial medication taken within two 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 two weeks, reported fever in the past 48 hours, or a temperature of ≥37.5 °C measured at the time of interview.Results: Submicroscopic 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 we limited the definition of fever 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.Conclusions: In 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.

Microscopic and submicroscopic Plasmodium infections in indigenous and non-indigenous communities in Colombia.

Background The indigenous population is considered a highly susceptible group to malaria becouse they usually live in areas with high Anopheles exposure and poverty, and have low access to health services. There is a great diversity of indigenous communities in Colombia living in malaria-endemic areas; however, the burden of infection in these populations has not extensively studied. This study aimed to determine the prevalence of Plasmodium infections in indigenous and non-indigenous communities in two malaria-endemic areas in Colombia.Methods A Community-based cross-sectional survey was conducted in seven villages of Turbo and El Bagre municipalities; three of these villages were indigenous communities. All inhabitants of all ages that were willing to participate were included. Sociodemographic and clinical data were recorded as well as household information. The parasitological diagnosis was performed by microscopy and nested PCR. The prevalence of microscopy and submicroscopic infection was estimated. An adjusted GEE model was used to explore risk factors associated with the infection.Results Among 713 participants, 60.1% were from indigenous communities. Plasmodium spp. was detected in 30 subjects (4.2%, CI 95% 2.9-5.9); from those, 29 were in the indigenous population, 47% of infections were afebrile, and most of them submicroscopic (10/14). Microscopic and submicroscopic prevalence was 2.5% (CI 95% 1.6-3.9) and 1.7% (CI 95% 0.9-2.9) respectively. In El Bagre, all infections occurred in indigenous participants (3.9%, CI 95% 2.2-7.1), and 81% were submicroscopic. By contrast, in Turbo, the highest prevalence occurred in indigenous people (11.5%; CI 95%: 7.3-17.5), but 88.8% were microscopic. Living in an indigenous population increased the incidence rate of infection compared with a non-indigenous population (IRR 19.4; CI 95% 2.3-166.7).Conclusion There is a high proportion of Plasmodium infection in indigenous communities. A substantial proportion of asymptomatic and submicroscopic carriers were detected. The identification of these infections, not only in indigenous but also in the non-indigenous population, as well as their associated factors, could help to implement specific malaria strategies for each context.

Impact of Submicroscopic Plasmodium falciparum Parasitaemia on Maternal Anaemia and Low Birth Weight in Blue Nile State, Sudan

The aim of the present study was to investigate the prevalence of submicroscopic infections and to assess its impact on maternal anaemia and low birth weight. A cross-sectional study was carried out with 1149 consented pregnant women who delivered at 3 main hospitals in the Blue Nile State, between January 2012 and December 2015. From a matched maternal peripheral, placental maternal side, and cord blood sample, blood films and dried spots were prepared for microscopic examination and nested polymerase chain reaction (n-PCR), respectively. 107 out of 447 negative blood films were found to have submicroscopic infection detected using n-PCR in any of the three compartments. Placental samples had a significantly higher prevalence (142) of submicroscopic infections compared with the peripheral (6.5%) and cord (8.1%) samples. The mean (SD) of the maternal haemoglobin (Hb) was significantly lower in cases with submicroscopic parasitaemia (10.9 (0.8) vs. 12.1 (0.7) g/dl, P<0.001) compared with those who had no submicroscopic parasitaemia. Submicroscopic malaria infection was associated with anaemia (OR 19.7, (95% CI, 10.3–37.8)). Thirty-eight babies born to women with submicroscopic infections were low birth weight (LBW) and was significantly lower in submicroscopic parasitaemia (2.663 (0.235) vs. 2.926 (0.341) kg, P<0.001). Submicroscopic malaria infection was associated with LBW (OR = 2.7, (95% CI, 1.2–5.6)). There is a high incidence of submicroscopic infections in any of the three compartments regardless of age or parity. Submicroscopic infection is a risk of maternal anaemia and low birth weight in women in this area of high seasonal malaria transmission.

PO 8249 SUBMICROSCOPIC PLASMODIUM FALCIPARUM INFECTIONS IN MATCHED PERIPHERAL, PLACENTAL AND UMBILICAL CORD BLOOD SAMPLES FROM CONGOLESE WOMEN AT DELIVERY

BackgroundThis cross-sectional study was conducted to characterise P. falciparum infections matched in peripheral, placental and cord blood among Congolese women at delivery receiving 1, 2 or more doses of sulfadoxine-pyrimethamine. The cross-sectional study was conducted in a Southern district of Brazzaville, Republic of the Congo, between March 2014 and April 2015.MethodsPeripheral and placental blood samples were collected for P. falciparum infection investigation by microscopy and nested polymerase chain reaction (PCR), using P. falciparum merozoite surface protein-2 (msp2) gene as marker.ResultsOf the 370 pregnant women recruited, only 7.3% peripheral and 2.7% placental blood samples were found smear-positive for P. falciparum by microscopy. All isolates from cord blood were microscopy-negative. However, the prevalences of submicroscopic P. falciparum infections (detectable only by PCR) were 25.4%, 16.7% and 9.4% in peripheral, placental and cord blood respectively. The frequency of 3D7 msp2 alleles was the highest (>60%) whatever the blood considered. We found a high prevalence of submicroscopic infection in pregnant women associated with a high genetic diversity of P. falciparum isolates. The multiplicity of infection ranged between 1.2 and 1.4 irrespective of the blood compartment, and it showed no significant association with maternal age (p=0.3), gravidity (p=0.1) or sulfadoxine-pyrimethamine (p=0.3).ConclusionIn summary, this study showed that there is a high prevalence of submicroscopic infection and a high genetic diversity of Plasmodium falciparum strains in Congo. This diversity varies according to maternal, placental and umbilical cord blood. Age, gravidity and doses of preventive treatment based on sulfadoxine-pyrimethamine do not interfere with the multiplicity of infections.

Global & Temporal Patterns of Submicroscopic Plasmodium falciparum Malaria Infection

Molecular detection of Plasmodium falciparum infection has revealed large numbers of individuals with low-density (yet transmissible) infections undetectable by microscopy. Here we present an updated systematic review of cross-sectional malaria surveys to explore the prevalence and drivers of these submicroscopic infections and define where they are likely to be relevant to malaria control efforts. Our results show that submicroscopic infections predominate in low transmission settings, but also reveal marked geographical variation in their prevalence, being highest in South American surveys and lowest in West African studies. Whilst current transmission levels partly explain these results, we find that historical transmission intensity also represents a crucial determinant of the size of the submicroscopic reservoir. Submicroscopic infection was more likely in adults than children, although we did not observe a statistically significant influence of seasonality. Our results suggest that the contribution of submicroscopic infections to transmission likely varies substantially across settings, potentially warranting different approaches to their targeting in the approach to elimination.

Community engagement for the rapid elimination of malaria: The case of Kayin State, Myanmar

Background: Currently, malaria elimination efforts are ongoing in several locations across Southeast Asia, including in Kayin State (also known as Karen State), Myanmar. This paper describes the community engagement efforts for a pilot malaria elimination project, the challenges encountered and lessons learnt. Methods: Between May 2013 and June 2015, a study on targeted malaria elimination (TME) that included mass drug administration was conducted in four villages (TPN, TOT, KNH, and HKT) of Kayin State. Community engagement efforts included workshops, meetings and house-to-house visits with community members. Exhibitions related to malaria and fun activities were organized for children. In addition, we provided primary care, small individual incentives and village-level incentives. This paper is based on our analysis of data extracted from meeting minutes, field notes, feedback sessions among staff and with community members as well as our own reflections. Results: Average participation across three rounds of MDA were 84.4%, 57.4%, 88.6% and 59.3% for TPN, TOT, KNH and HKT, respectively. Community engagement was fraught with practical challenges such as seasonal tasks of the villagers. There were challenges in explaining difficult concepts like drug resistance and submicroscopic infection. Another was understanding and navigating the politics of these villages, which are located in politically contested areas. Managing expectations of villagers was difficult as they assumed that the community team must know everything related to health. Conclusions: In the TME project, many different community engagement strategies were employed. We encountered many challenges which included logistical, scientific and political difficulties. An approach that is tailored to the local population is key.