Malaria Journal - Latest Articles

Efficacy of ICON(R) Maxx in the laboratory and against insecticide-resistant Anopheles gambiae in central Cote d'Ivoire

Mirko Winkler — 2012-05-15T00:00:00Z

Background: Long-lasting treatment kits, designed to transform untreated nets into long-lasting insecticidal nets (LLINs), may facilitate high coverage with LLINs where non-treated nets are in place. In this study, the efficacy of ICON(R) Maxx (Syngenta) was evaluated under laboratory conditions and in an experimental hut trial in central Cote d'Ivoire, where Anopheles gambiae s.s. are resistant to pyrethroid insecticides. Methods: In the laboratory, polyester and polyethylene net samples were treated with ICON(R) Maxx, washed up to 20 times and their efficacy determined in World Health Organization (WHO) cone assays against a susceptible laboratory An. gambiae s.s. colony. Over a 12-month period, the polyester nets were evaluated in a hut trial to determine mosquito deterrence, induced exophily, blood-feeding inhibition and mortality. Results: In the laboratory, ICON(R) Maxx-treated polyethylene nets showed higher efficacy against pyrethroid-susceptible mosquitoes than polyester nets. After 20 washings, insecticidal efficacy in bioassays was 59.4% knockdown (KD) and 22.3% mortality for polyethylene, and 55.3% KD and 17.9% mortality for polyester nets. In experimental huts, treated nets showed strong deterrence, induced exophily and an over three-fold reduction in blood-fed mosquitoes. More than half (61.8%) of the mosquitoes entering the huts with treated nets were found dead the next morning despite high levels of KD resistance. After washing the treated nets, KD and mortality rates were close to or exceeded predefined WHO thresholds in cone bioassays. Conclusion: In contrast to previous laboratory investigation, ICON(R) Maxx-treated nets showed only moderate KD and mortality rates. However, under semi-field conditions, in an area where mosquitoes are resistant to pyrethroids, ICON(R) Maxx showed high deterrence, induced exophily and provided a significant reduction in blood-feeding rates; features that are likely to have a positive impact in reducing malaria transmission. The WHO cone test may not always be a good proxy for predicting product performance under field conditions.

Improved methods for haemozoin quantification in tissues yield organ- and parasite-specific information in malariainfected mice

Katrien Deroost — 2012-05-14T00:00:00Z

Background: Despite intensive research, malaria remains a major health concern for non-immune residentsand travelers in malaria-endemic regions. Efficient adjunctive therapies against lifethreateningcomplications such as severe malarial anaemia, encephalopathy, placental malariaor respiratory problems are still lacking. Therefore, new insights into the pathogenesis ofsevere malaria are imperative. Haemozoin (Hz) or malaria pigment is produced during intraerythrocyticparasite replication, released in the circulation after schizont rupture andaccumulates inside multiple organs. Many in vitro and ex vivoimmunomodulating effects aredescribed for Hz but in vivo data are limited. This study aimed to improve methods for Hzquantification in tissues and to investigate the accumulation of Hz in different organs frommice infected with Plasmodium parasites with a varying degree of virulence. Methods: An improved method for extraction of Hz from tissues was elaborated and coupled to anoptimized, quantitative, microtiter plate-based luminescence assay with a high sensitivity. Inaddition, a technique for measuring Hz by semi-quantitative densitometry, applicable ontransmitted light images, was developed. The methods were applied to measure Hz in variousorgans of C57BL/6J mice infected with Plasmodium berghei ANKA, P. berghei NK65 orPlasmodium chabaudi AS. The used statistical methods were the Mann-Whitney U test andPearsons correlation analysis. Results: Most Hz was detected in livers and spleens, lower levels in lungs and kidneys, whereas subnanomolaramounts were observed in brains and hearts from infected mice, irrespectively ofthe parasite strain used. Furthermore, total Hz contents correlated with peripheralparasitaemia and were significantly higher in mice with a lethal P. berghei ANKA or P.berghei NK65-infection than in mice with a self-resolving P. chabaudi AS-infection, despitesimilar peripheral parasitaemia levels. Conclusions: The developed techniques were useful to quantify Hz in different organs with a highreproducibility and sensitivity. An organ-specific Hz deposition pattern was found and wasindependent of the parasite strain used. Highest Hz levels were identified in mice infectedwith lethal parasite strains suggesting that Hz accumulation in tissues is associated withmalaria-related mortality.

Remote sensing-based time series models for malaria early warning in the highlands of Ethiopia

Alemayehu Midekisa — 2012-05-14T00:00:00Z

Background: Malaria is one of the leading public health problems in most of sub-Saharan Africa,particularly in Ethiopia. Almost all demographic groups are at risk of malaria because ofseasonal and unstable transmission of the disease. Therefore, there is a need to developmalaria early-warning systems to enhance public health decision making for control andprevention of malaria epidemics. Data from orbiting earth-observing sensors can monitorenvironmental risk factors that trigger malaria epidemics. Remotely sensed environmentalindicators were used to examine the influences of climatic and environmental variability ontemporal patterns of malaria cases in the Amhara region of Ethiopia. Methods: In this study seasonal auto regressive integrated moving average (SARIMA) models wereused to quantify the relationship between malaria cases and remotely sensed environmentalvariables, including rainfall, land-surface temperature (LST), vegetation indices (NDVI andEVI), and actual evapotranspiration (ETa) with lags ranging from one to three months.Predictions from the best model with environmental variables were compared to the actualobservations from the last 12 months of the time series. Results: Malaria cases exhibited positive associations with LST at a lag of one month and positiveassociations with indicators of moisture (rainfall, EVI and ETa) at lags from one to threemonths. SARIMA models that included these environmental covariates had better fits andmore accurate predictions, as evidenced by lower AIC and RMSE values, than modelswithout environmental covariates. Conclusions: Malaria risk indicators such as satellite-based rainfall estimates, LST, EVI, and ETa exhibitedsignificant lagged associations with malaria cases in the Amhara region and improved modelfit and prediction accuracy. These variables can be monitored frequently and extensivelyacross large geographic areas using data from earth-observing sensors to support publichealth decisions.

Spatial repellents: from discovery and development to evidence-based validation

Nicole Achee — 2012-05-14T00:00:00Z

International public health workers are challenged by a burden of arthropod-borne disease thatremains elevated despite best efforts in control programmes. With this challenge comes theopportunity to develop novel vector control paradigms to guide product development andprogramme implementation. The role of vector behaviour modification in disease control wasfirst highlighted several decades ago but has received limited attention within the public healthcommunity. This paper presents current evidence highlighting the value of sub-lethal agents,specifically spatial repellents, and their use in global health, and identifies the primary challengestowards establishing a clearly defined and recommended role for spatial repellent products indisease control.

Isolation of Plasmodium falciparum by flow-cytometry: implications for single-trophozoite genotyping and parasite DNA purification for whole-genome high-throughput sequencing of archival samples

Anne Boissière — 2012-05-14T00:00:00Z

Background: Flow cytometry and cell sorting are powerful tools enabling the selection of particular cell types within heterogeneous cell mixtures. These techniques, combined with whole genome amplification that non-specifically amplify small amounts of starting DNA, offer exciting new opportunities for the study of malaria genetics. Among them, two are tested in this paper: (1) single cell genotyping and (2) parasite DNA purification for subsequent whole genome sequencing using shotgun technologies. Methods: The method described allows isolation of Plasmodium falciparum trophozoites, genotyping and whole genome sequencing from the blood of infected patients. For trophozoite isolation, parasite and host nuclei are stained using propidium iodide (PI) followed by flow cytometry and cell sorting to separate trophozoites from host cells. Before genotyping or sequencing, whole genome amplification is used to increase the amount of DNA within sorted samples. The method has been specifically designed to deal with frozen blood samples.Results and conclusionThe results demonstrate that single trophozoite genotyping is possible and that cell sorting can be successfully applied to reduce the contaminating host DNA for subsequent whole genome sequencing of parasites extracted from infected blood samples.

B cell analysis of ethnic groups in Mali with differential susceptibility to malaria

Silvia Portugal — 2012-05-11T00:00:00Z

Background: Several studies indicate that people of the Fulani ethnic group are less susceptible to malaria compared to those of other ethnic groups living sympatrically in Africa, including the Dogon ethnic group. Although the mechanisms of this protection remain unclear, the Fulani are known to have higher levels of Plasmodium falciparum-specific antibodies of all Ig classes as compared to the Dogon. However, the proportions of B cell subsets in the Fulani and Dogon that may account for differences in the levels of Ig have not been characterized. Methods: In this cross-sectional study, venous blood was collected from asymptomatic Fulani (n=25) and Dogon (n=25) adults in Mali during the malaria season, and from P. falciparum-naive adults in the U.S. (n=8). At the time of the blood collection, P. falciparum infection was detected by blood-smear in 16% of the Fulani and 40% of the Dogon volunteers. Thawed lymphocytes were analysed by flow cytometry to quantify B cell subsets, including immature and naive B cells; plasma cells; and classical, activated, and atypical memory B cells (MBCs). Results: The overall distribution of B cell subsets was similar between Fulani and Dogon adults, although the percentage of activated MBCs was higher in the Fulani group (Fulani: 11.07% [95% CI: 9.317 - 12.82]; Dogon: 8.31% [95% CI: 6.378 - 10.23]; P=0.016). The percentage of atypical MBCs was similar between Fulani and Dogon adults (Fulani: 28.3% [95% CI: 22.73 - 34.88]; Dogon: 29.3% [95% CI: 25.06 - 33.55], but higher than U.S. adults (U.S.: 3.0% [95% CI: -0.21 - 6.164]; P<0.001). Plasmodium falciparum infection was associated with a higher percentage of plasma cells among Fulani (Fulani infected: 3.3% [95% CI: 1.788 - 4.744]; Fulani uninfected: 1.71% [95% CI: 1.33 - 2.08]; P=0.011), but not Dogon adults. Conclusion: These data show that the malaria-resistant Fulani have a higher percentage of activated MBCs compared to the Dogon, and that P. falciparum infection is associated with a higher percentage of plasma cells in the Fulani compared to the Dogon, findings that may account for the higher levels of P. falciparum antibodies in the Fulani.

Is malaria illness among young children a cause or a consequence of low socioeconomic status? Evidence from the United Republic of Tanzania

Marcia Caldas de Castro — 2012-05-09T00:00:00Z

Background: Malaria is commonly considered a disease of the poor, but there is very little evidence of a possible two-way causality in the association between malaria and poverty. Until now, limitations to examine that dual relationship were the availability of representative data on confirmed malaria cases, the use of a good proxy for poverty, and accounting for endogeneity in regression models. Methods: A simultaneous equation model was estimated with nationally representative data for Tanzania that included malaria parasite testing with RDTs for young children (six-59 months), and accounted for environmental variables assembled with the aid of GIS. A wealth index based on assets, access to utilities/infrastructure, and housing characteristics was used as a proxy for socioeconomic status. Model estimation was done with instrumental variables regression. Results: Results show that households with a child who tested positive for malaria at the time of the survey had a wealth index that was, on average, 1.9 units lower (p-value < 0.001), and that an increase in the wealth index did not reveal significant effects on malaria. Conclusion: If malaria is indeed a cause of poverty, as the findings of this study suggest, then malaria control activities, and particularly the current efforts to eliminate/eradicate malaria, are much more than just a public health policy, but also a poverty alleviation strategy. However, if poverty has no causal effect on malaria, then poverty alleviation policies should not be advertised as having the potential additional effect of reducing the prevalence of malaria.

Mapping malaria risk among children in Cote d'Ivoire using Bayesian geo-statistical models

Giovanna Raso — 2012-05-09T00:00:00Z

Background: In Cote d'Ivoire, an estimated 767,000 disability-adjusted life years are due to malaria,placing the country at position number 14 with regard to the global burden of malaria. Riskmaps are important to guide control interventions, and hence, the aim of this study was topredict the geographical distribution of malaria infection risk in children aged <16 years inCote d'Ivoire at high spatial resolution. Methods: Using different data sources, a systematic review was carried out to compile and georeferencesurvey data on Plasmodium spp. infection prevalence in Cote d'Ivoire, focusing onchildren aged <16 years. The period from 1988 to 2007 was covered. A suite of Bayesiangeo-statistical logistic regression models was fitted to analyse malaria risk. Non-spatialmodels with and without exchangeable random effect parameters were compared tostationary and non-stationary spatial models. Non-stationarity was modelled assuming thatthe underlying spatial process is a mixture of separate stationary processes in each ecologicalzone. The best fitting model based on the deviance information criterion was used to predictPlasmodium spp. infection risk for entire Cote d'Ivoire, including uncertainty. Results: Overall, 235 data points at 170 unique survey locations with malaria prevalence data forindividuals aged <16 years were extracted. Most data points (n = 182, 77.4%) were collectedbetween 2000 and 2007. A Bayesian non-stationary regression model showed the best fit withannualized rainfall and maximum land surface temperature identified as significantenvironmental covariates. This model was used to predict malaria infection risk at nonsampledlocations. High-risk areas were mainly found in the north-central and western area,while relatively low-risk areas were located in the north at the country border, in the northeast,in the south-east around Abidjan, and in the central-west between two high prevalenceareas. Conclusion: The malaria risk map at high spatial resolution gives an important overview of thegeographical distribution of the disease in Cote d'Ivoire. It is a useful tool for the nationalmalaria control programme and can be utilized for spatial targeting of control interventionsand rational resource allocation.

Genetic variation of aldolase from Korean isolates of Plasmodium vivax and its usefulness in serodiagnosis

Jung-Yeon Kim — 2012-05-08T00:00:00Z

Background: The malaria aldolase is widely used as rapid diagnostic test (RDT), but the efficacy in aspectof its serological effectiveness in diagnosis is not known. The genetic variation of Koreanisolates was analysed and recombinant aldolase was evaluated as a serological antigen inPlasmodium vivax malaria. Methods: Genomic DNA was purified and the aldolase gene of P. vivax from 25 patients' bloodsamples was amplified. The samples came from 5 epidemic areas; Bucheon-si, Gimpo-si,Paju-si of Gyeonggido, Gangwha-gun of Incheon metropolitan city, and Cheorwon ofGangwon-do, South Korea. The antigenicity of the recombinant aldolase was tested bywestern blot and enzyme-linked immunosorbent assay (ELISA). Results: Sequence analysis of 25 Korean isolates of P. vivax showed that the open reading frame(ORF) of 1,110 nucleotides encoded a deduced protein of 369 amino acids (aa). This ORFshowed 100% homology with the P. vivax Sal I strain (XM_00165894) and P. vivax WDKstrain (AF247063), 87.4% homology with Plasmodium falciparum (AF179421), 90.6%homology with Plasmodium chabaudi (AF247060), 89.5% homology with Plasmodiumvinckei (AF247061), and 96.7% homology with Plasmodium knowlesi. A single nucleotidepolymorphism (SNP) at nucleotide 180 (G to A, n = 5) was also observed in the isolates. Theexpressed recombinant protein had a molecular weight of approximately 31 kDa (monomericform) and 62 kDa (dimeric form) as analysed by sodium dodecyl sulfate-polyacrylamide gelelectrophoresis (SDS-PAGE) analysis. Among 109 P. vivax patients, 32 (29.4%) had positivein an enzyme-linked absorbance assay (ELISA). This result showed significant correlationbetween ELISA and an indirect fluorescent antibody test (IFAT) (P < 0.0001). Conclusions: The aldolase gene from Korean isolates of P. vivax showed one SNP at nucleotide position180; this SNP mutant was discovered in only the western part of Han River, and included theregions of Ganghwa, Gimpo, and Bucheon. Based on the results, the relationship betweenantibody production against aldolase and the pattern of disease onset should be moreinvestigated before using aldolase for serodiagnosis.

Automated red blood cell exchange as an adjunctive treatment for severe Plasmodium falciparum malaria at the Vienna General Hospital in Austria: a retrospective cohort study

Lorenz Auer-Hackenberg — 2012-05-07T00:00:00Z

Background: Severe falciparum malaria is associated with considerable rates of mortality, despite theadministration of appropriate anti-malarial treatment. Since overall survival is associated withtotal parasite biomass, blood exchange transfusion has been proposed as a potential method torapidly reduce peripheral parasitaemia. However, current evidence suggests that thistreatment modality may not improve outcome. Automated red blood cell exchange (alsoreferred to as "erythrocytapheresis") has been advocated as an alternative method to rapidlyremove parasites from circulating blood without affecting patients' volume and electrolytestatus. However, only limited evidence from case reports and case series is available for thisadjunctive treatment. This retrospective cohort study describes the use of automated redblood cell exchange for the treatment of severe malaria at the Medical University of Vienna. Methods: Epidemiologic data for imported malaria cases in Austria are reported and data of patientstreated for malaria at the General Hospital/Medical University of Vienna were extracted fromelectronic hospital records. Results: Between 2000 and 2010, 146 patients were hospitalized at the Medical University of Viennadue to malaria and 16 of those were classified as severe malaria cases. Eleven patients of thiscohort were potentially eligible for an adjunctive treatment with automated red blood cellexchange. Five patients eventually underwent this procedure within a period of seven hours(range: 3-19 hours) after hospital admission. Six patients did not undergo this adjunctivetreatment following the decision of the treating physician. The procedure was well toleratedin all cases and rapid reduction in parasite counts was achieved without occurrence ofhaemodynamic complications. One patient died within seven days, whereas four patientssurvived without any sequelae.Discussion and conclusionAutomated red blood cell exchange was a safe and efficient procedure to rapidly clearperipheral parasitaemia. Whether the fast reduction in parasite biomass may ultimatelyimprove patient survival remains however unclear. Randomized controlled trials are neededto conclusively appreciate the value of this adjunctive treatment.