Areas Of Low Malaria Transmission Research Articles

Prevalence and determinants of anaemia in women of reproductive age in Sudan: analysis of a cross-sectional household survey

BackgroundAnaemia is a global health problem and women in reproductive age (WRA) are amongst the most affected population. Its consequences include low birth weight and maternal mortality. This study aimed to assess the prevalence of anaemia and to identify its determinants in Sudanese women in reproductive age.MethodsA population-based cross-sectional study was conducted in Sudan in 2016. A multi-stage stratified cluster sampling design was executed with consideration of rural population, urban population, and internally displaced persons/refugees camps residents. All women in reproductive age (15–49 years), classified by pregnancy status, in the targeted households were surveyed and personal characteristic data were collected. Their haemoglobin level and malaria infection (using rapid diagnostic test, RDT) were assessed. The World Health Organization (WHO) haemoglobin level cut-off for defining anaemia and severe anaemia in pregnant and non-pregnant women was used. Logistic regression analyses were performed.ResultsA total of 4271 women (WRA) of which 421 (9.9%) pregnant women (PW) were included in the study. The overall anaemia prevalence in WRA was 35.6%. It was 36.0 and 35.5% in PW and non-pregnant women (NPW), respectively. The average haemoglobin level was found to be 113.9 g/L (SD 16.3) and 123.2 g/L (SD 15.7) for PW and NPW respectively. Severe anaemia prevalence was 1.2% in each group. In the logistic regression model, anaemia was associated with malaria infection in PW (aOR 4.100, 95%CI 1.523–11.039, p = 0.003), NPW (aOR 2.776, 95%CI 1.889–4.080, p < 0.001), and WRA (aOR 2.885, 95%CI 2.021–4.119, p < 0.001). Other identified determinants of anaemia in NPW was living in camps (aOR 1.499, 95%CI 1.115–2.017, p = 0.007) and in WRA was being in the poorest economic class (aOR 1.436, 95%CI 1.065–1.936, p = 0.018).ConclusionsAnaemia is a public health problem in Sudan. The study supported the association between malaria infection and anaemia, but not with low and moderate malaria transmission areas. Resources need to be allocated for all anaemic populations with special attention for the populations in most need and interventions need to be implemented based on local variations. Malaria control interventions, specifically case management, may have a major impact in reducing anaemia prevalence in low to moderate malaria transmission areas.

Abstract A60: Transcriptional profile of CD56negCD16pos Natural Killer cells within endemic Burkitt lymphoma

Abstract Endemic Burkitt lymphoma (eBL), the most common pediatric cancer in equatorial Africa, has long been associated with two etiologic agents: Epstein-Barr virus (EBV) and Plasmodium falciparum malaria. On the other hand, Natural Killer (NK) cells are essential in the clearance of infected cells as well as play a critical role in tumor immunosurveillance. Despite chronic viral infections as HIV, HCV, which have been found to promote the expansion of a CD56 (negative) NK cell subset with impaired effector function, previous cancer studies have been limited to investigations of CD56dimCD16pos NK cells. We previously published that eBL children had significantly more CD56negCD16pos NK cells compared to age-matched healthy children from a low and high malaria transmission area. Here, we characterized this CD56negCD16pos NK subset using histology staining, multicolor flow cytometry, and RNA-sequencing. We found CD56negCD16pos NK cells to be morphologically similar to CD56dimCD16pos NK cells but had higher expression of FCGR3B (CD16b) (p=0.000008) and MPEG1 (Perforin 2) (p=0.0000007), and lower expression of KLRF1 (NKp80), IL18RAP and IL18R1 (IL18 receptor) (p=0.000003, p=0.000003 and p=0.00005, respectively). Phenotypically, CD56negCD16pos NK cells share characteristics of adaptive NK cells; however, they differ from “memory-like” NK cells, with consistent expression of NKG2C/CD57, lower expression of NKp46 and CD160, and higher expression of KIR3DL1 compared to CD56dimCD16pos NK cells. Finally, higher plasma levels of IL-12p70 and IL-2 (known to help NK cell activation and proliferation) and IL-6 and MIP1a were found in healthy compared to eBL children. Together, these findings suggest that the expansion of CD56negCD16pos NK cells could help explain diminished tumor immunosurveillance and might be a mechanism by which EBV-infected cells evades NK-cell mediated immunity. Citation Format: Catherine S. Forconi, Cliff Oduor, John M. Ong’echa, Jeff Bailey, Ann M. Moormann. Transcriptional profile of CD56negCD16pos Natural Killer cells within endemic Burkitt lymphoma [abstract]. In: Proceedings of the AACR Special Conference on the Advances in Pediatric Cancer Research; 2019 Sep 17-20; Montreal, QC, Canada. Philadelphia (PA): AACR; Cancer Res 2020;80(14 Suppl):Abstract nr A60.

Parasite density in severe malaria in Colombia.

BackgroundColombia has officially adopted the parasite density levels of severe malaria established by the WHO (>50,000 parasites/μl). These values have been inferred from areas of high transmission in Africa and are not consistent with the dynamics of low and unstable transmission in Colombia. The objective of this study was therefore to determine the parasite density values observed in patients with severe malaria and their distribution in the different ecoepidemiological regions of Colombia.MethodsA retrospective and descriptive study of confirmed cases of severe malaria was conducted in endemic areas of malaria in Colombia over the period 2014–2017. Data were collected from secondary sources of the Subnational Programs of Malaria Prevention and Control. Person, place, and time variables were selected. The official definition of severe malaria was adopted, and compliance with these criteria was determined. Univariate and bivariate analyses were conducted with absolute and relative frequency measures, and the relevant statistical tests were applied.ResultsThe overall parasite density values in Colombia showed a geometric mean of 5,919 parasites/μl (95% CI: 5,608–6,248). By parasite species, the values were 6,151 (95% CI: 5,631–6,718) for Plasmodium falciparum and 5,815 (95% CI: 5,428–6,230) for Plasmodium vivax. The highest parasite density values were recorded in the Amazon ecoepidemiological region (8,177; 95% CI: 6,015–11,116), and the lowest values were recorded in the Andean region (5,026; 95% CI: 2,409–10,480).ConclusionsIn endemic areas of low and unstable malaria transmission in the Colombian territory, the parasite density levels observed in populations with severe malaria are lower than the officially established values. The parasite density criterion is not really a relevant criterion for the definition of severe cases in Colombia and it certainly not be used to make a clinical decision about the severity of the disease.

Emergence of Undetectable Malaria Parasites: A Threat under the Radar amid the COVID-19 Pandemic?

.Rapid diagnostic tests (RDTs) play a critical role in malaria diagnosis and control. The emergence of Plasmodium falciparum parasites that can evade detection by RDTs threatens control and elimination efforts. These parasites lack or have altered genes encoding histidine-rich proteins (HRPs) 2 and 3, the antigens recognized by HRP2-based RDTs. Surveillance of such parasites is dependent on identifying false-negative RDT results among suspected malaria cases, a task made more challenging during the current pandemic because of the overlap of symptoms between malaria and COVID-19, particularly in areas of low malaria transmission. Here, we share our perspective on the emergence of P. falciparum parasites lacking HRP2 and HRP3, and the surveillance needed to identify them amid the COVID-19 pandemic.

Low exposure to Plasmodium falciparum and Acquisition of Antibodies to Circumsporozoite Protein Antigens in Individuals Living in Western Highlands of Kenya with Unstable Malaria Transmission

Background: Malaria continues to be a major public health concern despite the concerted efforts to eliminate it. Antibodies to Plasmodium falciparum (P. falciparum) antigens are involved in prevention of infection and disease with some of the antigens being targeted as lead candidates in vaccine development. However, most of the studies have been done in malaria endemic areas with little information available on exposure and acquisition of protective antibodies in areas of low and unstable malaria transmission. This study sought to determine whether the extent of exposure to P. falciparum affect acquisition of protective antibodies by measuring antibody levels and determine the prevalence of circumsporozoite protein (CSP) and crude schizont extract (SE) in individuals living in an area with low unstable malaria transmission in Western Highlands of Kenya.Methods: Sixty plasma samples from individuals living in an area of low unstable malaria transmission in Western Highlands of Kenya were randomly selected and categorized into three age groups: 18years (n=14). Antibodies levels in plasma were measured by Enzyme Linked Immunosorbent Assay (ELISA) and compared to known positive and negative control plasma samples. Prevalence and levels of antibodies produced against circumsporozoite protein and schizont extract antigens were compared between age groups.Results. The prevalence of antibodies ranged from 0% to 14.29% at arbitrary units (AU)>2 for the two antigens. The antibody prevalence did not significantly increase with age (P>0.05) but correlated with CSP and SE antigens (r=0.5977; P<0.05).Conclusion This study highlights antibody responses to CSP and SE antigens in individuals living in low and unstable malaria transmission. The levels of antibodies were generally low across all age groups and there were no significant differences among age groups. Longitudinal study on more antigens is needed to inform exploration of multi-antigen vaccines and also adopt several control measures including Epidemic Preparedness and Response (EPR).

Identification and Pilot Evaluation of Salivary Peptides from Anopheles albimanus as Biomarkers for Bite Exposure and Malaria Infection in Colombia.

Insect saliva induces significant antibody responses associated with the intensity of exposure to bites and the risk of disease in humans. Several salivary biomarkers have been characterized to determine exposure intensity to Old World Anopheles mosquito species. However, new tools are needed to quantify the intensity of human exposure to Anopheles bites and understand the risk of malaria in low-transmission areas in the Americas. To address this need, we conducted proteomic and bioinformatic analyses of immunogenic candidate proteins present in the saliva of uninfected Anopheles albimanus from two separate colonies—one originating from Central America (STECLA strain) and one originating from South America (Cartagena strain). A ~65 kDa band was identified by IgG antibodies in serum samples from healthy volunteers living in a malaria endemic area in Colombia, and a total of five peptides were designed from the sequences of two immunogenic candidate proteins that were shared by both strains. ELISA-based testing of human IgG antibody levels against the peptides revealed that the transferrin-derived peptides, TRANS-P1, TRANS-P2 and a salivary peroxidase peptide (PEROX-P3) were able to distinguish between malaria-infected and uninfected groups. Interestingly, IgG antibody levels against PEROX-P3 were significantly lower in people that have never experienced malaria, suggesting that it may be a good marker for mosquito bite exposure in naïve populations such as travelers and deployed military personnel. In addition, the strength of the differences in the IgG levels against the peptides varied according to location, suggesting that the peptides may able to detect differences in intensities of bite exposure according to the mosquito population density. Thus, the An. albimanus salivary peptides TRANS-P1, TRANS-P2, and PEROX-P3 are promising biomarkers that could be exploited in a quantitative immunoassay for determination of human-vector contact and calculation of disease risk.

The persistence of naturally acquired antibodies and memory B cells specific to rhoptry proteins of Plasmodium vivax in patients from areas of low malaria transmission

BackgroundRhoptries are the large, paired, secretory organelles located at the apical tip of the malaria merozoite that are considered important for parasite invasion processes. Plasmodium vivax rhoptry proteins have been shown to induce humoral immunity during natural infections. Therefore, these proteins may be potential novel vaccine candidates. However, there is a lack of data on the duration of antibody and memory B cell (MBC) responses. Here, the longitudinal analysis of antibody and MBC responses to the P. vivax rhoptry proteins PvRALP1-Ecto and PvRhopH2 were monitored and analysed in individuals to determine their persistence.MethodsThirty-nine samples from P. vivax-infected subjects (age 18–60 years) were recruited to explore the frequency and persistence of antibody and MBC responses against rhoptry proteins (PvRALP1-Ecto and PvRhopH2) using both cross-sectional and longitudinal cohort study designs. Antibody levels were determined by ELISA during clinical malaria, and at 3, 9 and 12 months post-infection. The frequency of MBC sub-sets and presence of rhoptry-specific MBCs in subjects 18 months after treatment were detected by flow cytometry and ELISPOT assay.ResultsThe seroprevalence of antibodies against PvRALP1-Ecto and PvRhopH2 proteins was found to be high during acute infection, with IgG1, IgG2 and IgG3 sub-classes predominant. However, these anti-rhoptry responses were short-lived and significantly decreased at 9 months post-infection. To relate the durability of these antibody responses to MBC persistence at post-infection, 18-month post-infection peripheral blood mononuclear cells (PBMCs) samples were taken to detect rhoptry-specific MBCs and frequency of MBC sub-sets, and correlate with antibody responses. These late post-infection samples revealed that rhoptry-specific MBCs were present in about 70% of total subjects. However, the persistence of specific MBCs was not correlated with antibody responses as the majority of malaria subjects who were positive for PvRALP1-Ecto- or PvRhopH2-specific MBCs were seronegative for the rhoptry antigens. The frequencies of classical MBCs were increased after infection, whereas those of activated and atypical MBCs were decreased, indicating that MBC responses could switch from activated or atypical MBCs to classical MBCs after parasite clearance, and were maintained in blood circulating at post-infection.ConclusionThe study showed that rhoptry antigens induced the development and persistence of MBC responses in P. vivax-infected subjects who lived in a region of low malaria transmission, which were not related to the longevity of antibody responses.

Malaria Prevalence in a Low Transmission Area, Jazan District of Southwestern Saudi Arabia.

Detailed description of malaria in low transmission areas is crucial for elimination. The current study aimed to provide a comprehensive description for malaria transmission in Jazan, a low transmission district, southwestern Saudi Arabia. Patients at a tertiary care hospital were recruited in our study between August 2016 and September 2018. Malaria diagnosis was performed through a species-specific nested polymerase chain reaction (nested PCR), microscopy and Paramax-3TM rapid detection test (RDT). Malaria was detected in 30 patients by the PCR, with point prevalence of 10.9%. Of these malaria infections, 80% was imported, 26.6% was asymptomatic and 23.3% was sub-microscopic. Malaria was reported throughout the year, with February/March and September/October peaks. Infection was significantly more in males than in females (P=0.01). Likewise, infections were detected more in febrile than in non-febrile patients (P=0.01). Adult aged 15–24 years, fever and travel were identified as high-risk factors. Malaria was primarily attributed to Plasmodium falciparum mono-infections, followed by P. vivax mono-infections and lastly to falciparum/vivax mixed infections accounting 76.6%, 16.6%, and 6.6% of PCR-confirmed malaria cases, respectively. The nested PCR was superior to the smear microscopy (sensitivity 76.6%; specificity 100%) and the RDT (sensitivity 83.3%, specificity 94.2%). The overall percent agreement between microscopy and the RDT was 92.7% (kappa=0.63). High proportion of imported malaria including sub-microscopic and sub-patent cases were described. We suggest that incorporation of molecular tool into the conventional malaria diagnosis is beneficial in Jazan district.

Evidence of asymptomatic submicroscopic malaria in low transmission areas in Belaga district, Kapit division, Sarawak, Malaysia

BackgroundMalaysia has declared its aim to eliminate malaria with a goal of achieving zero local transmission by the year 2020. However, targeting the human reservoir of infection, including those with asymptomatic infection is required to achieve malaria elimination. Diagnosing asymptomatic malaria is not as straightforward due to the obvious lack of clinical manifestations and often subpatent level of parasites. Accurate diagnosis of malaria is important for providing realistic estimates of malaria burden and preventing misinformed interventions. Low levels of parasitaemia acts as silent reservoir of transmission thus remains infectious to susceptible mosquito vectors. Hence, the aim of this study is to investigate the prevalence of asymptomatic submicroscopic malaria (SMM) in the District of Belaga, Sarawak.MethodsIn 2013, a total of 1744 dried blood spots (DBS) were obtained from residents of 8 longhouses who appeared healthy. Subsequently, 251 venous blood samples were collected from residents of 2 localities in 2014 based on the highest number of submicroscopic cases from prior findings. Thin and thick blood films were prepared from blood obtained from all participants in this study. Microscopic examination were carried out on all samples and a nested and nested multiplex PCR were performed on samples collected in 2013 and 2014 respectively.ResultsNo malaria parasites were detected in all the Giemsa-stained blood films. However, of the 1744 samples, 29 (1.7%) were positive for Plasmodium vivax by PCR. Additionally, of the 251 samples, the most prevalent mono-infection detected by PCR was Plasmodium falciparum 50 (20%), followed by P. vivax 39 (16%), P. knowlesi 9 (4%), and mixed infections 20 (8%).ConclusionsThis research findings conclude evidence of Plasmodium by PCR, among samples previously undetectable by routine blood film microscopic examination, in local ethnic minority who are clinically healthy. SMM in Belaga district is attributed not only to P. vivax, but also to P. falciparum and P. knowlesi. In complementing efforts of programme managers, there is a need to increase surveillance for SMM nationwide to estimate the degree of SMM that warrant measures to block new transmission of malaria.

Evaluation of the effectiveness of a targeted community-based IRS approach for malaria elimination in an area of low malaria transmission of the central-western Senegal

The implementation of effective malaria control strategies in the central-western Senegal, such as Indoor Residual Spraying (IRS), long-lasting insecticide-treated nets (LLIN), Seasonal malaria chemoprophylaxis (SMC) and appropriate management of malaria cases, has led to the decline of malaria transmission in the region. However, residual malaria transmission still occurring in some localities, known as hotspots villages, making challenging the achievement of the malaria elimination goal. A pilot study was undertaken between 2013 and 2014 to test the feasibility of a community-based IRS approach for malaria elimination in four targeted health districts of the Central Western Senegal.The residual efficacy of the Actellic® 300CS formulation on the sprayed surface was monitored using WHO cone test.Overall, 615 walls were tested over the two successive years, respectively 240 and 375 in 2013 and 2014 IRS campaigns. The residual efficacy of the IRS with Actellic®300 CS was longer in the second year due to the improvement of community agents spraying skill the second year thanks to the refreshing training and a better supervision by professional agent of the National Hygiene Service. The analysis of the Incidence Rate Ratio under the Poisson model shows no significant difference of IRS effectiveness according to the building type.In conclusion, the quality of training of community agents and good supervision of IRS activities play a key role in the quality and the residual efficacy of IRS campaigns. A good planning and implementation of IRS campaign ensure a high quality and a good effectiveness of spraying with the Actellic®300 CS formulation.

Epidemiological profiles of recurrent malaria episodes in an endemic area along the Thailand-Myanmar border: a prospective cohort study

BackgroundIn low malaria transmission areas, many people acquire multiple malaria infections within a single season. This study aimed to describe the pattern and epidemiological profile of malaria recurrence in a hypoendemic area of western Thailand and identify factors associated with having multiple malaria episodes.MethodsAn open cohort of 7000 residents in seven clusters along the Thai-Myanmar border was followed during a 6.5-year period (2011–mid 2017). Symptomatic and asymptomatic malaria infections were detected by passive case detection (PCD), weekly household visit, and mass blood surveys every 4–6 months. Malaria recurrence was defined as subsequent parasitaemic episodes occurred later than 7 days after receiving anti-malarial treatment. This study focused on analysis of recurrent episodes that occurred within 1 year after treatment. Numbers of malaria cases with single and multiple episodes were compared between clusters. Kaplan–Meier curve was performed to determine the intervals of recurrent episodes by Plasmodium species and age groups. The ordinal logistic model was used to determine factors associated with multiple malaria episodes, and to compare with single episodes, and those with no malaria infection.ResultsThe cumulative incidence of malaria in the study area was 5.2% over the 6.5 years. Overall, 410 malaria patients were detected. Of these patients, 20% and 16% had multiple malaria episodes during the entire period and within 1 year after initial treatment, respectively. About 80% of repeated malaria episodes were caused by the same Plasmodium species as the primary infections. The median interval and interquartile range (IQR) between the first and second episode was 88 (43–175) days for all parasites, 56 (35–133) days for two Plasmodium falciparum episodes, and 90 (59–204) days for two Plasmodium vivax episodes. The interval between the episodes was increased with age. Factors significantly associated with multiple episodes of malaria infection included male sex, young age, Karen ethnicity, forest-related occupation, and having other malaria infected persons in the same house in the same period.ConclusionsPeople who have multiple malaria episodes may play an important role in maintaining malaria transmission in the area. Understanding epidemiological profiles of this group is important for planning strategies to achieve the elimination goal.

Comparative Analysis of Igg Responses to Recombinant Qβ Phage Displayed MSP3 and UB05 in Dual HIV-Malaria Infected Adults Living in areas differing in Malaria Transmission Intensities

Immunoglobulin G (IgG) specific responses against Plasmodium falciparum merozoite antigens such as the merozoite surface protein 3 (MSP3) and UB05 are known to play critical roles in parasiteamia control and protection from symptomatic illness. However when there is intense perennial malaria transmission coupled with concurrent infection with the human immunodeficiency virus type 1 (HIV), knowledge of IgG antibody response profiles is limited. In this study we assessed the impact of dual HIV-Malaria infections on IgG subclass responses to MSP3 (QβMSP3) and UB05 (QβUB05) in individuals living in two areas of Cameroon differing in malaria transmission intensity. We observed differences in antigen specific IgG and IgG subclass responses which were dependent upon the antigen type, malaria transmission intensity, HIV infection, malaria infection and dual HIV-malaria infections. Individuals living in high malaria transmission areas irrespective of HIV or malaria status had significantly higher IgG responses to both antigens (P=0.0001 for QβMSP3, P=0.0001 for QβUB05) than their counterpart from low transmission areas. When dual HIV-Malaria infection is considered significantly higher QβMSP3 specific IgG1 (P=0.0001) and IgG3 (P=0.04) responses in double negative individuals was associated with protection against malaria in low transmission areas. Increased QβUB05 specific IgG1 responses (P=0.0001) in double negative individuals were associated with protection in high transmission areas in contrast to significantly higher IgG3 responses to QβUB05 (P=0.0001) which were more relevant to protection in low malaria transmission areas in the same population. These findings imply that QβMSP3 might not be suitable as a standalone vaccine in areas differing in transmission intensity. However, antigenicity of UB05 most likely predicts immunity in both low and high transmission areas and could be used either alone or in combination with other antigens for vaccine studies in areas differing in transmission intensities. Understanding immune responses to QβUB05 and QβMSP3 could thus enable the development of efficacious vaccines or commensurate immunotherapeutic strategies suitable for areas differing in malaria transmission intensity.

Self-medication with non-prescribed pharmaceutical agents in an area of low malaria transmission in northern Tanzania: a community-based survey.

BackgroundSelf-treatment with antimicrobials is common in sub-Saharan Africa. Little is known about the prevalence of this practice where malaria transmission intensity is low, and little is known about the prevalence of self-treatment with other medications such as antihypertensives and antihyperglycemics.MethodsA two-stage randomized population-based cluster survey with selection proportional to population size was performed in northern Tanzania. Self-identified healthcare decision-makers from randomly selected households were asked to report instances of self-medication without a prescription in the preceding year. Associations between self-treatment and sociodemographic characteristics were assessed with Pearson’s chi-squared and the Student’s t-test.ResultsA total of 718 participants completed the survey, and 344 (47.9%) reported any household member obtaining medication without a prescription. Of these, 85 (11.8%) obtained an antimicrobial and four (0.6%) obtained an antihypertensive or antihyperglycemic. Of respondents reporting self-treatment, 306 (89.0%) selected the medication themselves. Self-treatment with antimicrobials was associated with post-primary education (OR 1.95, 95% CI 1.22–3.16, p=0.005), younger age (43.1 vs 48.7 years, p=0.007) and higher socioeconomic status score (0.42 vs 0.34, p=0.023).ConclusionsSelf-treatment with antimicrobials in an area of low malaria transmission intensity was uncommon and self-treatment with antihypertensives and antihyperglycemics was rare.

The economic cost of malaria at the household level in high and low transmission areas of central India

The cost burden of malaria at the household level, resulting from complex social, economic, and epidemiological factors, is enormous. This study was carried out to estimate the economic burden of malaria at the household level in low and high malaria transmission areas of central India. We conducted surveys with households in which at least one member had suffered from malaria in the three months preceding the survey. The human capital method was used to estimate the cost of malaria at the household level. We found that the total cost per episode of malaria was higher in high transmission areas than low transmission areas; direct costs were generally higher for adults than for children. Males spent more on diagnosis and treatment than females, and the mean work absenteeism due to malaria was higher among male adult patients than among females, though work time lost due to child illness was lower for male caregivers. Households belonging to high and middle socioeconomic status (SES) spent significantly more on malaria illness than those of low SES. However, the economic burden of malaria relative to annual incomes was highest among low SES households. Populations belonging to high transmission areas were more vulnerable to malarial infection due to geo-climatic, demographic, socioeconomic, and cultural factors, as well as the relatively poor access to health facilities that characterize these regions. Additionally, poor health-seeking practices not only increase the cost burden but also adversely affect patients' health and productivity, which lead to opportunity losses while imposing a greater economic burden on households.

The prevalence of submicroscopic Plasmodium falciparum gametocyte carriage and multiplicity of infection in children, pregnant women and adults in a low malaria transmission area in Southern Ghana

BackgroundThe gametocyte stage of Plasmodium falciparum is considered an important target for disrupting malaria transmission. Indications are that various demographic groups, such as children and pregnant women may differ in risk of harbouring gametocytes, which may be crucial for targeted control. In this study, the relationship between the prevalence and multiplicity of P. falciparum, asexual parasite infections and gametocytaemia was assessed in three different demographic groups in an area of southern Ghana with low malaria endemicity. Levels of antibody responses to Pfs230 were also assessed as a proxy for the presence of gametocytes.MethodsThe study involved multiple cross-sectional sampling of children (N = 184, aged 2–15 years), male and non-pregnant female adults (N = 154, aged 16–65 years) and pregnant women (N = 125, aged 18–45 years) from Asutsuare in the Shai Osudoku District of Greater Accra Region in Ghana. Asexual parasitaemia was detected by microscopy and PCR, and gametocytaemia was assessed by Pfs25-real time PCR. Multiclonal P. falciparum infections were estimated by msp2 genotyping and an indirect ELISA was used to measure plasma IgG antibodies to Pfs230 antigen.ResultsOverall, children and pregnant women had higher prevalence of submicroscopic gametocytes (39.5% and 29.7%, respectively) compared to adults (17.4%). Multiplicity of infection observed amongst children (3.1) and pregnant women (3.9) were found to be significantly higher (P = 0.006) compared with adults (2.7). Risk of gametocyte carriage was higher in individuals infected with P. falciparum having both Pfmsp2 3D7 and FC27 parasite types (OR = 5.92, 95% CI 1.56–22.54, P = 0.009) compared with those infected with only 3D7 or FC27 parasite types. In agreement with the parasite prevalence data, anti-Pfs230 antibody levels were lower in gametocyte positive adults (β = − 0.57, 95% CI − 0.81, − 0.34, P < 0.001) compared to children.ConclusionsThese findings suggest that children and pregnant women are particularly important as P. falciparum submicroscopic gametocyte reservoirs and represent important focus groups for control interventions. The number of clones increased in individuals carrying gametocytes compared to those who did not carry gametocytes. The higher anti-gametocyte antibody levels in children suggests recent exposure and may be a marker of gametocyte carriage.

Diagnostic accuracy of loop-mediated isothermal amplification (LAMP) for screening malaria in peripheral and placental blood samples from pregnant women in Colombia

BackgroundPregnant women frequently show low-density Plasmodium infections that require more sensitive methods for accurate diagnosis and early treatment of malaria. This is particularly relevant in low-malaria transmission areas, where intermittent preventive treatment is not recommended. Molecular methods, such as polymerase chain reaction (PCR) are highly sensitive, but require sophisticated equipment and advanced training. Instead, loop mediated isothermal amplification (LAMP) provides an opportunity for molecular detection of malaria infections in remote endemic areas, outside a reference laboratory. The aim of the study is to evaluate the performance of LAMP for the screening of malaria in pregnant women in Colombia.MethodsThis is a nested prospective study that uses data and samples from a larger cross-sectional project conducted from May 2016 to January 2017 in three Colombian endemic areas (El Bagre, Quibdó, and Tumaco). A total of 531 peripheral and placental samples from pregnant women self-presenting at local hospitals for antenatal care visits, at delivery or seeking medical care for suspected malaria were collected. Samples were analysed for Plasmodium parasites by light microscopy (LM), rapid diagnostic test (RDT) and LAMP. Diagnostic accuracy endpoints (sensitivity, specificity, predictive values, and kappa scores) of LM, RDT and LAMP were compared with nested PCR (nPCR) as the reference standard.ResultsIn peripheral samples, LAMP showed an improved sensitivity (100.0%) when compared with LM 79.5% and RDT 76.9% (p < 0.01), particularly in afebrile women, for which LAMP sensitivity was two-times higher than LM and RDT. Overall agreement among LAMP and nPCR was high (kappa value = 1.0). Specificity was similar in all tests (100%). In placental blood, LAMP evidenced a four-fold improvement in sensitivity (88.9%) when compared with LM and RDT (22.2%), being the only method, together with nPCR, able to detect placental infections in peripheral blood.ConclusionsLAMP is a simple, rapid and accurate molecular tool for detecting gestational and placental malaria, being able to overcome the limited sensitivity of LM and RDT. These findings could guide maternal health programs in low-transmission settings to integrate LAMP in their surveillance systems for the active detection of low-density infections and asymptomatic malaria cases.

Persistence of Long-lived Memory B Cells specific to Duffy Binding Protein in individuals exposed to Plasmodium vivax

The major challenge in designing a protective Duffy binding protein region II (DBPII)-based vaccine against blood-stage vivax malaria is the high number of polymorphisms in critical residues targeted by binding-inhibitory antibodies. Here, longevity of antibody and memory B cell response (MBCs) to DBL-TH variants, DBL-TH2, -TH4, -TH5, -TH6 and -TH9 were analyzed in P. vivax-exposed individuals living in a low malaria transmission area of southern Thailand. Antibody to DBL-TH variants were significantly detected during P. vivax infection and it was persisted for up to 9 months post-infection. However, DBL-TH-specific MBC responses were stably maintained longer than antibody response, at least 3 years post-infection in the absence of re-infection. Phenotyping of B cell subsets showed the expansion of activated and atypical MBCs during acute and recovery phase of infection. While the persistence of DBL-TH-specific MBCs was found in individuals who had activated and atypical MBC expansion, anti-DBL-TH antibody responses was rapidly declined in plasma. The data suggested that these two MBCs were triggered by P. vivax infection, its expansion and stability may have impact on antibody responses. Our results provided evidence for ability of DBPII variant antigens in induction of long-lasting MBCs among individuals who were living in low malaria endemicity.

Entomological impact of indoor residual spraying with pirimiphos-methyl: a pilot study in an area of low malaria transmission in Senegal

BackgroundScaling-up of effective anti-malarial control strategies in Central-West region of Senegal has resulted in the sharp decline in malaria prevalence in this area. However, despite these strategies, residual malaria transmission has been observed in some villages (hot spots). The objective of this study was to assess the impact of indoor residual spraying (IRS) with pirimiphos-methyl on malaria transmission in hot spot areas.MethodsThe malaria vector population dynamics were monitored in each of the six selected villages (4 of which used IRS, 2 were unsprayed control areas) using overnight human landing catches (HLC) and pyrethrum spray catches (PSC). The host source of blood meals from freshly fed females collected using PSC was identified using the direct ELISA method. Females caught through HLC were tested by ELISA for the detection of Plasmodium falciparum circumsporozoite protein and Anopheles gambiae complex was identified using PCR.ResultsPreliminary data shown that the densities of Anopheles populations were significantly lower in the sprayed areas (179/702) compared to the control. Overall, malaria transmission risk was 14 times lower in the intervention zone (0.94) compared to the control zone (12.7). In the control areas, three Anopheles species belonging to the Gambiae complex (Anopheles arabiensis, Anopheles coluzzii and Anopheles melas) maintained the transmission, while only An. coluzzii was infective in the sprayed areas.ConclusionThe preliminary data from this pilot study showed that IRS with the CS formulation of pirimiphos-methyl is likely very effective in reducing malaria transmission risk. However, additional studies including further longitudinal entomological surveys as well as ecological and ethological and genetical characterization of vectors species and their populations are needed to better characterize the entomological impact of indoor residual spraying with pirimiphos-methyl in the residual transmission areas of Senegal.

The persistence and oscillations of submicroscopic Plasmodium falciparum and Plasmodium vivax infections over time in Vietnam: an open cohort study

SummaryBackgroundA substantial proportion of Plasmodium species infections are asymptomatic with densities too low to be detectable with standard diagnostic techniques. The importance of such asymptomatic plasmodium infections in malaria transmission is probably related to their duration and density. To explore the duration of asymptomatic plasmodium infections and changes in parasite densities over time, a cohort of participants who were infected with Plasmodium parasites was observed over a 2-year follow-up period.MethodsIn this open cohort study, inhabitants of four villages in Vietnam were invited to participate in baseline and subsequent 3-monthly surveys up to 24 months, which included the collection of venous blood samples. Samples were batch-screened using ultra-sensitive (u)PCR (lower limit of detection of 22 parasites per mL). Participants found to be infected by uPCR during any of these surveys were invited to join a prospective cohort and provide monthly blood samples. We estimated the persistence of Plasmodium falciparum and Plasmodium vivax infections and changes in parasite densities over a study period of 24 months.FindingsBetween Dec 1, 2013, and Jan 8, 2016, 356 villagers participated in between one and 22 surveys. These study participants underwent 4248 uPCR evaluations (11·9 tests per participant). 1874 (32%) of 4248 uPCR tests indicated a plasmodium infection; 679 (36%) of 1874 tests were P falciparum monoinfections, 507 (27%) were P vivax monoinfections, 463 (25%) were co-infections with P falciparum and P vivax, and 225 (12%) were indeterminate species of Plasmodium. The median duration of P falciparum infection was 2 months (IQR 1–3); after accounting for censoring, participants had a 20% chance of having parasitaemia for 4 months or longer. The median duration of P vivax infection was 6 months (3–9), and participants had a 59% chance of having parasitaemia for 4 months or longer. The parasite densities of persistent infections oscillated; following ultralow-density infections, high-density infections developed frequently.InterpretationPersistent largely asymptomatic P vivax and P falciparum infections are common in this area of low seasonal malaria transmission. Infections with low-density parasitaemias can develop into much higher density infections at a later time, which are likely to sustain malaria endemicity.FundingThe Wellcome Trust, Bill & Melinda Gates Foundation.

Community-led Responses for Elimination (CoRE): a study protocol for a community randomized controlled trial assessing the effectiveness of community-level, reactive focal drug administration for reducing Plasmodium falciparum infection prevalence and incidence in Southern Province, Zambia

BackgroundZambia is pushing for, and has made great strides towards, the elimination of malaria transmission in Southern Province. Reactive focal test and treat (RFTAT) using rapid diagnostic tests and artemether-lumefantrine (AL) has been key in making this progress. Reactive focal drug administration (RFDA) using dihydroartemisinin-piperaquine (DHAP), may be superior in accelerating clearance of the parasite reservoir in humans due to the provision of enhanced chemoprophylactic protection of at-risk populations against new infections. The primary aim of this study is to quantify the relative effectiveness of RFDA with DHAP against RFTAT with AL (standard of care) for reducing Plasmodium falciparum prevalence and incidence.Methods/designThe study will be conducted in four districts in Southern Province, Zambia; an area of low malaria transmission and high coverage of vector control. A community randomized controlled trial of 16 health facility catchment areas will be used to evaluate the impact of sustained year-round routine RFDA for 2 years, relative to a control of year-round routine RFTAT. Reactive case detection will be triggered by a confirmed malaria case, e.g., by microscopy or rapid diagnostic test at any government health facility. Reactive responses will be performed by community health workers (CHW) within 7 days of the index case confirmation date. Responses will be performed out to a radius of 140 m from the index case household. A subset of responses will be followed longitudinally for 90 days to examine reinfection rates. Primary outcomes include a post-intervention survey of malaria seropositivity (n = 4800 children aged 1 month to under 5 years old) and a difference-in-differences analysis of malaria parasite incidence, as measured through routine passive case detection at health facilities enrolled in the study. The study is powered to detect approximately a 65% relative reduction in these outcomes between the intervention versus the control.DiscussionStrengths of this trial include a robust study design and an endline cross-sectional parasite survey as well as a longitudinal sample. Primary limitations include statistical power to detect only a 65% reduction in primary outcomes, and the potential for contamination to dilute the effects of the intervention.Trial registrationClinicalTrials.gov, ID: NCT02654912. Registered on 12 November 2015.