Declining Malaria Transmission Research Articles

Microheterogeneity of Transmission Shapes Submicroscopic Malaria Carriage in Coastal Tanzania.

Asymptomatic carriage of malaria parasites persists even as malaria transmission declines. Low-density infections are often submicroscopic, not detected with rapid diagnostic tests (RDTs) or microscopy but detectable by polymerase chain reaction (PCR). To characterize submicroscopic Plasmodium falciparum carriage in an area of declining malaria transmission, asymptomatic persons >5 years of age in rural Bagamoyo District, Tanzania, were screened using RDT, microscopy, and PCR. We investigated the size of the submicroscopic reservoir of infection across villages, determined factors associated with submicroscopic carriage, and assessed the natural history of submicroscopic malaria over 4 weeks. Among 6076 participants, P. falciparum prevalences by RDT, microscopy, and PCR were 9%, 9%, and 28%, respectively, with roughly two-thirds of PCR-positive individuals harboring submicroscopic infection. Adult status, female sex, dry season months, screened windows, and bed net use were associated with submicroscopic carriage. Among 15 villages encompassing 80% of participants, the proportion of submicroscopic carriers increased with decreasing village-level malaria prevalence. Over 4 weeks, 23% of submicroscopic carriers (61 of 266) became RDT positive, with half exhibiting symptoms, while half (133 of 266) were no longer parasitemic at the end of 4 weeks. Progression to RDT-positive patent malaria occurred more frequently in villages with higher malaria prevalence. Microheterogeneity in transmission observed at the village level appears to affect both the size of the submicroscopic reservoir and the likelihood of submicroscopic carriers developing patent malaria in coastal Tanzania.

Antibody-Dependent Respiratory Burst against Plasmodium falciparum Merozoites in Individuals Living in an Area with Declining Malaria Transmission.

Malaria transmission intensity affects the development of naturally acquired immunity to malaria. An absolute correlate measure of protection against malaria is lacking. However, antibody-mediated functions against Plasmodium falciparum correlate with protection against malaria. In children, antibody-mediated functions against P. falciparum decline with reduced exposure. It is unclear whether adults maintain antibody-mediated functions as malaria transmission declines. This study assessed antibody-dependent respiratory burst (ADRB) in individuals from an area with declining malaria transmission. In an age-matched analysis, we compare ADRB activity during high versus low malaria transmission periods. Age significantly predicted higher ADRB activity in the high (p < 0.001) and low (p < 0.001) malaria transmission periods. ADRB activity was higher during the high compared to the low malaria transmission period in older children and adults. Only older adults during the high malaria transmission period had their median ADRB activity above the ADRB cut-off. Ongoing P. falciparum infection influenced ADRB activity during the low (p = 0.01) but not the high (p = 0.29) malaria transmission period. These findings propose that naturally acquired immunity to P. falciparum is affected in children and adults as malaria transmission declines, implying that vaccines will be necessary to induce and maintain protection against malaria.

Serology reveals micro-differences in Plasmodium falciparum transmission in the Hohoe municipality of Ghana

BackgroundWith the decline in malaria transmission due to global efforts, a more sensitive tool is needed to monitor transmission intensity and pattern at the micro-level. Though transmission in a broader area may be similar, factors such as sanitation, practices of open water storage, early morning and evening activities, outdoor sleeping and agricultural practices within communities could cause differences in exposure and thus transmission. This study thus probed malaria transmission at a micro-level using serology in the Hohoe Municipality of Ghana.MethodsThis cross-sectional study involved 327 asymptomatic children aged 1-12 years in both rural (196) and urban (131) communities in the Hohoe municipality. Total IgG responses specific for three P. falciparum antigens (CSP, MSP2-FC27, MSP2-3D7) were determined in plasma eluted from dried blood spots using indirect ELISA.ResultsA higher proportion of individuals in the rural area had parasites by both microscopy and PCR. Total IgG levels and seroprevalence were higher in rural compared to urban communities (p&amp;lt;0.05). In a multiple regression model, adjusting for confounders, levels of PfMSP2-3D7-specific IgG was associated with the higher transmission which occurs in the rural community.ConclusionThe results suggest that though the district is categorized as having medium malaria transmission, differences within settlements may influence malaria transmission reflecting in antibody levels and prevalence of malaria antigen-specific IgG.

Gravidity and malaria trends interact to modify P. falciparum densities and detectability in pregnancy: a 3-year prospective multi-site observational study

BackgroundLow-density Plasmodium falciparum infections prevail in low transmission settings, where immunity is expected to be minimal, suggesting an immune-independent effect on parasite densities. We aimed to describe parasite densities in pregnancy, and determine how gravidity and antibody-mediated immunity affect these, during a period of declining malaria transmission in southern Mozambique.MethodsWe documented P. falciparum infections at first antenatal care visits (n = 6471) between November 2016 and October 2019 in Ilha Josina (high-to-moderate transmission area), Manhiça (low transmission area), and Magude (pre-elimination area). Two-way interactions in mixed-effects regression models were used to assess gravidity-dependent differences in quantitative PCR-determined P. falciparum positivity rates (PfPRqPCR) and densities, in the relative proportion of detectable infections (pDi) with current diagnostic tests (≥ 100 parasites/μL) and in antimalarial antibodies.ResultsPfPRqPCR declined from 28 to 13% in Ilha Josina and from 5–7 to 2% in Magude and Manhiça. In primigravidae, pDi was highest in Ilha Josina at the first study year (p = 0.048), which declined with falling PfPRqPCR (relative change/year: 0.41, 95% CI [0.08; 0.73], p = 0.029), with no differences in antibody levels. Higher parasite densities in primigravidae from Ilha Josina during the first year were accompanied by a larger reduction of maternal hemoglobin levels (− 1.60, 95% CI [− 2.49; − 0.72; p < 0.001), than in Magude (− 0.76, 95% CI [− 1.51; − 0.01]; p = 0.047) and Manhiça (− 0.44, 95% CI [− 0.99; 0.10; p = 0.112). In contrast, multigravidae during the transmission peak in Ilha Josina carried the lowest pDi (p = 0.049). As PfPRqPCR declined, geometric mean of parasite densities increased (4.63, 95% CI [1.28; 16.82], p = 0.020), and antibody levels declined among secundigravidae from Ilha Josina.ConclusionsThe proportion of detectable and clinically relevant infections is the highest in primigravid women from high-to-moderate transmission settings and decreases with declining malaria. In contrast, the falling malaria trends are accompanied by increased parasite densities and reduced humoral immunity among secundigravidae. Factors other than acquired immunity thus emerge as potentially important for producing less detectable infections among primigravidae during marked declines in malaria transmission.

Trends of malaria infection in pregnancy in Ghana over the past two decades: a review

BackgroundThere has been a global decline in malaria transmission over the past decade. However, not much is known of the impact of this observation on the burden of malaria infection in pregnancy in endemic regions including Ghana. A narrative review was undertaken to help describe trends in malaria infection in pregnancy in Ghana. Among others, such information is important in showing any progress made in malaria in pregnancy control.MethodsTo describe trends in pregnancy-associated malaria infection in Ghana, a search and review of literature reporting data on the prevalence of asymptomatic Plasmodium falciparum infection in pregnancy was conducted.ResultsThirty-six (36) studies, conducted over 1994–2019, were included in the review. In the northern savannah zone with largely seasonal malaria transmission, prevalence appeared to reduce from about 50–60% in 1994–2010 to 13–26% by 2019. In the middle transitional/forest zone, where transmission is perennial with peaks in the rainy season, prevalence apparently reduced from 60% in the late 1990 s to about 5–20% by 2018. In the coastal savannah area, there was apparent reduction from 28 to 35% in 2003–2010 to 5–11% by 2018–2019. The burden of malaria infection in pregnancy continues to be highest among teenagers and younger-aged pregnant women and paucigravidae.ConclusionsThere appears to be a decline in asymptomatic parasite prevalence in pregnancy in Ghana though this has not been uniform across the different transmission zones. The greatest declines were noticeably in urban settings. Submicroscopic parasitaemia remains a challenge for control efforts. Further studies are needed to evaluate the impact of the reduced parasite prevalence on maternal anaemia and low birthweight and to assess the local burden of submicroscopic parasitaemia in relation to pregnancy outcomes.

Do clinicians in areas of declining malaria transmission adhere to malaria diagnosis guidelines? A cross-sectional study from Kampala, Uganda

BackgroundUganda's clinical management guidelines recommend a malaria laboratory test in all patients presenting with fever (history of fever or an axillary temperature ≥ 37.5 °C), and only those with a positive test receive anti-malarial treatment. However, the current practice in areas with declining malaria transmission remains unknown. This study assessed the clinicians’ diagnostic practices, the factors associated with recommending a test, and the risk of missing a malaria case when a test is not recommended in patients presenting with fever in Kampala, an area of declining malaria transmission in Uganda.MethodsBetween January and March 2020, 383 participants aged ≥ 12 years and presenting to Kisenyi Health Centre IV in Kampala district with fever were enrolled in the study. A questionnaire was administered during exit interviews, routine diagnostic practices were recorded from participant clinical notes, and a research blood slide was obtained for later reading.ResultsOf the enrolled participants, 356 (93%) had a malaria diagnostic test recommended by the clinician. Factors associated with increasing prevalence of having a test recommended included; history of overnight travel (adjusted prevalence ratio [aPR] 1.07, 95% confidence interval [CI] 1.02–1.13, p = 0.011), being married (aPR = 1.07, 95% CI 1.01–1.13, p = 0.022), and having tertiary education (aPR = 1.09 95% CI 1.01–1.17, p = 0.031). Among the 27 participants where a malaria diagnostic test was not recommended, 4 (14.8%) had a positive study smear.ConclusionDespite having significant declines in malaria transmission in Kampala in the last decade, clinicians at the study health facility highly adhered to the clinical management guidelines, recommending a malaria test in almost all patients presenting with fever. However, a significant proportion of malaria cases was missed when a test was not recommended. These results highlight the importance of laboratory testing for malaria in all patients who present with fevers and live in endemic settings even when the transmission has significantly declined.

Impact of a Rapid Decline in Malaria Transmission on Antimalarial IgG Subclasses and Avidity.

Understanding how immunity to malaria is affected by declining transmission is important to aid vaccine design and understand disease resurgence. Both IgG subclasses and avidity of antigen-specific responses are important components of an effective immune response. Using a multiplex bead array assay, we measured the total IgG, IgG subclasses, and avidity profiles of responses to 18 P. falciparum blood stage antigens in samples from 160 Ugandans collected at two time points during high malaria transmission and two time points following a dramatic reduction in transmission. Results demonstrated that, for the antigens tested, (i) the rate of decay of total IgG following infection declined with age and was driven consistently by the decrease in IgG3 and occasionally the decrease in IgG1; (ii) the proportion of IgG3 relative to IgG1 in the absence of infection increased with age; (iii) the increase in avidity index (the strength of association between the antibody and antigen) following infection was largely due to a rapid loss of non-avid compared to avid total IgG; and (iv) both avid and non-avid total IgG in the absence of infection increased with age. Further studies are required to understand the functional differences between IgG1 and IgG3 in order to determine their contribution to the longevity of protective immunity to malaria. Measuring changes in antibody avidity may be a better approach of detecting affinity maturation compared to avidity index due to the differential expansion and contraction of high and low avidity total IgG.

Diagnostic performance of HRP2-only malaria rapid diagnostic test in Ghanaian pregnant women with asymptomatic peripheral blood infection: the case of First Response® test kit

Background: The use of malaria rapid diagnostic test(RDT) enables targeted treatment that mitigates against the development of parasite drug resistance. With detection thresholds at ≥200 parasites/μL, their diagnostic performance in pregnant women may be challenging as asymptomatic infections with low parasite densities are common. Few data exist on the performance of histidine-rich protein-2 (HRP2) RDTs in Ghanaian pregnant women considering commonly occurring low parasite densities. Objective: The study sought to contribute more knowledge on test performance on First Response® test kit to guide the continuous evaluation of HRP2 RDTs in pregnancy. Methods: As part of an antimalarial drug trial in pregnancy, First Response® RDT results were compared to microscopy of peripheral blood slides in 1664 women. The diagnostic performance indicators were computed as proportions with 95% confidence intervals. The risk of having a positive RDT result was computed for age, gravidity and parasite density using binomial regression methods. Results: Parasitaemia prevalence by microscopy was 5.71%(n =95/1664) while that by RDT was 21.57%(n = 359/1664). Sensitivity was 82.11% (n=78/95), specificity was 82.09% (n=1288/1569), positive predictive value was 21.73% (n=78/359), and the likelihood ratio for a positive test was 4.58. False-negative RDT results were recorded for low parasite densities as well as densities ≥ 200/ μL while false-positive results were recorded in 281of 1664 tests. Primigravidae and younger aged women were more likely to have positive RDT results compared to multigravidae and women aged ≥ 30 yr. Conclusion: The moderate sensitivity, specificity and other diagnostic parameters reported suggest the First Response® malaria RDT is useful for detecting peripheral parasitaemia in pregnant women but the use of HRP2-only RDTs is limited by the existence of parasites with HRP2 gene deletion. The use of RDTs based on combined antigens continues to be recommended. Further research is needed on RDT performance in pregnant women with declining malaria transmission.

Aetiology of acute febrile illness in children in a high malaria transmission area in West Africa

ObjectivesAreas with declining malaria transmission in sub-Saharan Africa have recently witnessed important changes in the aetiology of childhood acute febrile illness (AFI). We describe the aetiology of AFI in a high malaria transmission area in rural Burkina Faso. MethodsIn a prospective hospital-based diagnostic study, children aged 3 months to 15 years with AFI were recruited and assessed using a systematic diagnostic protocol, including blood cultures, whole blood PCR on a selection of bacterial pathogens, malaria diagnostics and a multiplex PCR on nasopharyngeal swabs targeting 21 viral and 4 bacterial respiratory pathogens. ResultsA total of 589 children with AFI were enrolled from whom an infectious disease was considered in 575 cases. Acute respiratory tract infections, malaria and invasive bacterial infections (IBI) accounted for 179 (31.1%), 175 (30.4%) and 75 (13%) of AFI cases respectively; 16 (21.3%) of IBI cases also had malarial parasitaemia. A viral pathogen was demonstrated from the nasopharynx in 157 children (90.7%) with respiratory tract symptoms. Of all children with viral respiratory tract infections, 154 (92.4% received antibiotics, whereas no antibiotic was provided in 13 (17%) of IBI cases. ConclusionsViral respiratory infections are a common cause of childhood AFI in high malaria transmission areas, next to malaria and IBI. These findings highlight the importance of interventions to improve targeted treatment with antimicrobials. Most patients with viral infections received antibiotics unnecessarily, while a considerable number with IBI did not receive antibiotics.

The Unmet Need: Low Performance of Laboratory Professionals in Malaria Microscopy, Oromia Regional State, Ethiopia.

Ethiopia aims to diagnose and treat all clinical malaria within 24 hours of fever onset in its stride to eliminate the disease by 2030. Microscopy remains to be the mainstay for diagnosis at the health center and hospital level. Continuous evaluation and performance upgrading of malaria microscopists is one of the cornerstones in this effort. We assessed the performance of malaria microscopists compared with reference readers in diagnosing, identifying the species, and quantifying parasitemia. A total of 174 microscopists were enrolled from health facilities located in 86 districts in Oromia region (Ethiopia) from January 2017 to June 2018. Panel slides with known Plasmodium species, diagnostic blood stage, and parasite density were prepared by the reference readers. Sociodemographics, education, in-service training, and routine practice of participants were captured. Sensitivity, specificity, percent agreement, and kappa score were calculated. An overall low performance was observed that could threaten the malaria diagnostic service. Of all the slides distributed (1,218), only 17.0% of the positive and 30.0% of the negative slides were correctly identified and 22.4% were correctly quantified. Compared with the reference readers, participants had lower competence in diagnosing (74.3% agreement and kappa 0.45) and identifying the species (71.2% agreement and kappa 0.40). Two-fifths of the participants were graded as "in training" with respect to identifying the species (41.0%) and the diagnostic stages (40.0%). An in-service training/retraining and supportive supervision are needed to raise and maintain the competence of microscopists in settings with a recent decline in malaria transmission and aiming for ultimate elimination of the disease.

Apical membrane protein 1‐specific antibody profile and temporal changes in peripheral blood B‐cell populations in Plasmodium vivax malaria

Plasmodium falciparum-specific antibodies tend to be short-lived, but their cognate memory B cells (MBCs) circulate in the peripheral blood of exposed subjects for several months or years after the last infection. However, the time course of antigen-specific antibodies and B-cell responses to the relatively neglected parasite Plasmodium vivax remains largely unexplored. Here, we showed that uncomplicated vivax malaria elicits short-lived antibodies but long-lived MBC responses to a major blood-stage P vivax antigen, apical membrane protein 1 (PvAMA-1), in subjects exposed to declining malaria transmission in the Amazon Basin of Brazil. We found that atypical (CD19+ CD10- CD21- CD27- ) MBCs, which appear to share a common precursor with classical MBCs but are unable to differentiate into antibody-secreting cells, significantly outnumbered classical MBCs by 5:1 in the peripheral blood of adult subjects currently or recently infected with P vivax and by 3:1 in healthy residents in the same endemic communities. We concluded that malaria can drive classical MBCs to differentiate into functionally impaired MBCs not only in subjects repeatedly exposed to P falciparum, but also in subjects living in areas with low levels of P vivax transmission in the Amazon, leading to an impaired B-cell memory that may affect both naturally acquired and vaccine-induced immunity.

Prospects and strategies for malaria elimination in the Greater Mekong Sub-region: a qualitative study

BackgroundAs malaria elimination becomes a goal in malaria-endemic nations, questions of feasibility become critical. This article explores the potential challenges associated with this goal and future strategies for malaria elimination in the Greater Mekong Sub-region.MethodsThirty-two semi-structured interviews were conducted with policy makers (n = 17) and principal investigators (n = 15) selected based on their involvement in malaria prevention, control and elimination in the GMS. Interviews were audio-recorded and transcribed for qualitative content (thematic) analysis using QSR NVivo.ResultsAll respondents described current malaria control and elimination strategies, such as case detection and management, prevention and strengthening of surveillance systems as critical and of equal priority. Aware of the emergence of multi-drug resistance in the GMS, researchers and policy makers outlined the need for additional elimination tools. As opposed to a centralized strategy, more targeted and tailored approaches to elimination were recommended. These included targeting endemic areas, consideration for local epidemiology and malaria species, and strengthening the peripheral health system. A decline in malaria transmission could lead to complacency amongst funders and policy makers resulting in a reduction or discontinuation of support for malaria elimination. Strong commitment of policymakers combined with strict monitoring and supervision by funders were considered pivotal to successful elimination programmes.ConclusionAgainst a backdrop of increasing anti-malarial resistance and decreasing choices of anti-malarial regimens, policy makers and researchers stressed the urgency of finding new malaria elimination strategies. There was consensus that multi-pronged strategies and approaches are needed, that no single potential tool/strategy can be appropriate to all settings. Hence there is a need to customize malaria control and elimination strategies based on the better surveillance data.

Reduced mosquito survival in metal-roof houses may contribute to a decline in malaria transmission in sub-Saharan Africa

In The Gambia, metal-roof houses were hotter during the day than thatched-roof houses. After 24 h, the mortality of Anopheles gambiae, the principal African malaria vector, was 38% higher in metal-roof houses than thatched ones. During the day, mosquitoes in metal-roof houses moved from the hot roof to cooler places near the floor, where the temperature was still high, reaching 35 °C. In laboratory studies, at 35 °C few mosquitoes survived 10 days, the minimum period required for malaria parasite development. Analysis of epidemiological data showed there was less malaria and lower vector survival rates in Gambian villages with a higher proportion of metal roofs. Our findings are consistent with the hypothesis that the indoor climate of metal-roof houses, with higher temperatures and lower humidity, reduces survivorship of indoor-resting mosquitoes and may have contributed to the observed reduction in malaria burden in parts of sub-Saharan Africa.

Ten years malaria trend at Arjo-Didessa sugar development site and its vicinity, Southwest Ethiopia: a retrospective study

BackgroundThe trend analysis of malaria data from health facilities is useful for understanding dynamics of malaria epidemiology and inform for future malaria control planning. Changes in clinical malaria characteristics, like gender and age distribution are good indicators of declining malaria transmission. This study was conducted to determine the malaria trend at Arjo-Didessa sugar development site and its vicinity, southwest Ethiopia, from 2008 to 2017.MethodsMonthly malaria confirmed case data from 2008 to 2017 was extracted from 11 health facilities based on clinical registers at Arjo sugar development site and its vicinity, southwest Ethiopia. Both positivity rate and malaria incidence rate were calculated. Changes in malaria parasite species and seasonality were analysed; age structure and gender distribution were compared between different study periods. Trend in malaria incidence and climatic impact were analysed and past LLIN and IRS campaigns were used as dynamics modifier.ResultsOver a period of 10 years, 54,020 blood film were collected for malaria diagnosis in the health facilities at the area, of which 18,049 (33.4%) were confirmed malaria cases by both microscopically and RDT. Plasmodium falciparum, Plasmodium vivax, and mixed infection (P. falciparum and P. vivax) accounted for 8660 (48%), 7649 (42.4%), and 1740 (9.6%) of the malaria cases, respectively. The study also revealed that P. vivax was the predominant over P. falciparum for 4 years (2010, 2014, 2015 and 2016). There was a remarkable reduction of overall malaria infection during the 10 years. Malaria has been reported in all age groups, but age distribution showed that vast majority of cases were adults age 15 years and above 13,305 (73.7%). In all age groups, males were more significantly affected than females (χ2 = 133.0, df = 2, P < 0.0001). Moreover, malaria positivity rate showed a strong seasonality (χ2 = 777.55, df = 11, P < 0.0001). However, malaria cases were reported in all seasons across 10 years in the study area.ConclusionIn general, malaria positivity showed a declining trend over 10 years period in the area. However, current prevalence shows it is public health burden and needs attention for further intensification of interventions. In the study area, both P. falciparum and P. vivax co-exist and P. vivax is more prevalent than P. falciparum in almost half of the years. Therefore, malaria interventions should be strengthened in the study area.

Serological evidence for a decline in malaria transmission following major scale-up of control efforts in a setting selected for Plasmodium vivax and Plasmodium falciparum malaria elimination in Babile district, Oromia, Ethiopia.

BackgroundFollowing successful malaria control during the last decade, Ethiopia instituted a stepwise malaria elimination strategy in selected low-transmission areas.MethodsCross-sectional surveys were conducted in Babile district, Oromia, Ethiopia from July to November 2017 to evaluate malaria infection status using microscopy and nested polymerase chain reaction (nPCR) and serological markers of exposure targeting Plasmodium falciparum and Plasmodium vivax apical membrane antigen-1 (AMA-1).ResultsParasite prevalence was 1.2% (14/1135) and 5.1% (58/1143) for P. falciparum and 0.4% (5/1135) and 3.6% (41/1143) for P. vivax by microscopy and nPCR, respectively. Antibody prevalence was associated with current infection by nPCR for both P. falciparum (p<0.001) and P. vivax (p=0.014) and showed an age-dependent increase (p<0.001, for both species). Seroconversion curves indicated a decline in malaria exposure 15 y prior to sampling for P. falciparum and 11.5 y prior to sampling for P. vivax, broadly following malaria incidence data from district health offices, with higher antibody titres in adults than children for both species.ConclusionsMalaria transmission declined substantially in the region with continuing heterogeneous but measurable local transmission, arguing in favour of continued and tailored control efforts to accelerate the progress towards elimination efforts.

Consistent signatures of selection from genomic analysis of pairs of temporal and spatial Plasmodium falciparum populations from The Gambia

Genome sequences of 247 Plasmodium falciparum isolates collected in The Gambia in 2008 and 2014 were analysed to identify changes possibly related to the scale-up of antimalarial interventions that occurred during this period. Overall, there were 15 regions across the genomes with signatures of positive selection. Five of these were sweeps around known drug resistance and antigenic loci. Signatures at antigenic loci such as thrombospodin related adhesive protein (Pftrap) were most frequent in eastern Gambia, where parasite prevalence and transmission remain high. There was a strong temporal differentiation at a non-synonymous SNP in a cysteine desulfarase (Pfnfs) involved in iron-sulphur complex biogenesis. During the 7-year period, the frequency of the lysine variant at codon 65 (Pfnfs-Q65K) increased by 22% (10% to 32%) in the Greater Banjul area. Between 2014 and 2015, the frequency of this variant increased by 6% (20% to 26%) in eastern Gambia. IC50 for lumefantrine was significantly higher in Pfnfs-65K isolates. This is probably the first evidence of directional selection on Pfnfs or linked loci by lumefantrine. Given the declining malaria transmission, the consequent loss of population immunity, and sustained drug pressure, it is important to monitor Gambian P. falciparum populations for further signs of adaptation.

Widespread mosquito net fishing in the Barotse floodplain: Evidence from qualitative interviews.

BackgroundThe insecticide-treated mosquito net (ITN) is a crucial component of malaria control programs, and has prevented many malaria cases and deaths due to scale up. ITNs also serve effectively as fishing nets and various sources have reported use of ITNs for fishing. This article examines how widespread the practice of mosquito net fishing with ITNs is.MethodsWe conducted in-depth interviews with fishery personnel and traditional leadership from the Barotse Royal Establishment in Western Province, Zambia, to better understand the presence or absence of the use of ITNs as fishing nets. We then coded the interviews for themes through content analysis. Additionally we conducted a desk review of survey data to show trends in malaria indicators, nutritional status of the population and fish consumption.ResultsAll those interviewed reported that ITNs are regularly used for fishing in Western Zambia and the misuse is widespread. Concurrently those interviewed reported declines in fish catches both in terms of quantity and quality leading to threatened food security in the area. In addition to unsustainable fishing practices those interviewed referenced drought and population pressure as reasons for fishery decline. Malaria indicators do not show a trend in declining malaria transmission, fish consumption has dropped dramatically and nutritional status has not improved over time.ConclusionsDespite the misuse of the ITNs for fishing all those interviewed maintained that ITN distribution should continue. Donors, control programs and scientists should realize that misuse of ITNs as fishing nets is a current problem for malaria control and potentially for food security that needs to be addressed.

Increasingly inbred and fragmented populations of Plasmodium vivax associated with the eastward decline in malaria transmission across the Southwest Pacific.

The human malaria parasite Plasmodium vivax is more resistant to malaria control strategies than Plasmodium falciparum, and maintains high genetic diversity even when transmission is low. To investigate whether declining P. vivax transmission leads to increasing population structure that would facilitate elimination, we genotyped samples from across the Southwest Pacific region, which experiences an eastward decline in malaria transmission, as well as samples from two time points at one site (Tetere, Solomon Islands) during intensified malaria control. Analysis of 887 P. vivax microsatellite haplotypes from hyperendemic Papua New Guinea (PNG, n = 443), meso-hyperendemic Solomon Islands (n = 420), and hypoendemic Vanuatu (n = 24) revealed increasing population structure and multilocus linkage disequilibrium yet a modest decline in diversity as transmission decreases over space and time. In Solomon Islands, which has had sustained control efforts for 20 years, and Vanuatu, which has experienced sustained low transmission for many years, significant population structure was observed at different spatial scales. We conclude that control efforts will eventually impact P. vivax population structure and with sustained pressure, populations may eventually fragment into a limited number of clustered foci that could be targeted for elimination.

Status of insecticide resistance in malaria vectors in Kwale County, Coastal Kenya

BackgroundThe strategy for malaria vector control in the context of reducing malaria morbidity and mortality has been the scale-up of long-lasting insecticidal nets to universal coverage and indoor residual spraying. This has led to significant decline in malaria transmission. However, these vector control strategies rely on insecticides which are threatened by insecticide resistance. In this study the status of pyrethroid resistance in malaria vectors and it’s implication in malaria transmission at the Kenyan Coast was investigated.ResultsUsing World Health Organization diagnostic bioassay, levels of phenotypic resistance to permethrin and deltamethrin was determined. Anopheles arabiensis showed high resistance to pyrethroids while Anopheles gambiae sensu stricto (s.s.) and Anopheles funestus showed low resistance and susceptibility, respectively. Anopheles gambiae sensu lato (s.l.) mosquitoes were further genotyped for L1014S and L1014F kdr mutation by real time PCR. An allele frequency of 1.33% for L1014S with no L1014F was detected. To evaluate the implication of pyrethroid resistance on malaria transmission, Plasmodium falciparum infection rates in field collected adult mosquitoes was determined using enzyme linked immunosorbent assay and further, the behaviour of the vectors was assessed by comparing indoor and outdoor proportions of mosquitoes collected. Sporozoite infection rate was observed at 4.94 and 2.60% in An. funestus s.l. and An. gambiae s.l., respectively. A higher density of malaria vectors was collected outdoor and this also corresponded with high Plasmodium infection rates outdoor.ConclusionsThis study showed phenotypic resistance to pyrethroids and low frequency of L1014S kdr mutation in An. gambiae s.l. The occurrence of phenotypic resistance with low levels of kdr frequencies highlights the need to investigate other mechanisms of resistance. Despite being susceptible to pyrethroids An. funestus s.l. could be driving malaria infections in the area.

Modelling dynamic change of malaria transmission in holoendemic setting (Dielmo, Senegal) using longitudinal measures of antibody prevalence to Plasmodium falciparum crude schizonts extract

BackgroundEvaluation of local Plasmodium falciparum malaria transmission has been investigated previously using the reversible catalytic model based on prevalence of antibody responses to single antigen to estimate seroconversion rates. High correlations were observed between seroconversion rates and entomological inoculation rates (EIR). However, in this model, the effects of malaria control interventions and clinical episodes on serological measurements were not assessed. This study monitors the use of antibody responses to P. falciparum crude extracts for assessing malaria transmission, compares seroconversion rates estimated from longitudinal data to those derived from cross-sectional surveys and investigates the effects of malaria control interventions on these measures in an area of declining malaria transmission. In addition, the validity of this model was evaluated by comparison with the alternative model.MethodsFive cross-sectional surveys were carried out at the end of the wet season in Dielmo, a malaria-endemic Senegalese rural area in 2000, 2002, 2008, 2010 and 2012. Antibodies against schizonts crude extract of a local P. falciparum strain adapted to culture (Pf 07/03) were measured by ELISA. Age-specific seroprevalence model was used both for cross-sectional surveys and longitudinal data (combined data of all surveys).ResultsA total of 1504 plasma samples obtained through several years follow-up of 350 subjects was used in this study. Seroconversion rates based on P. falciparum schizonts crude extract were estimated for each cross-sectional survey and were found strongly correlated with EIR. High variability between SCRs from cross-sectional and longitudinal surveys was observed. In longitudinal studies, the alternative catalytic reversible model adjusted better with serological data than the catalytic model. Clinical malaria attacks and malaria control interventions were found to have significant effect on seroconversion.DiscussionThe results of the study suggested that crude extract was a good serological tool that could be used to assess the level of malaria exposure in areas where malaria transmission is declining. However, additional parameters such as clinical malaria and malaria control interventions must be taken into account for determining serological measurements for more accuracy in transmission assessment.