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Malaria remains a threat to public health in Malawi. It is well acknowledged that malaria research and robust evidence can have an impact on malaria policy and practice, resulting in positive population health gains. We report policy-relevant research contributions that the Malawi International Center of Excellence for Malaria Research (ICEMR) in partnership with local and international collaborators has made. Findings from our ICEMR studies have shown that long-lasting insecticide-treated bed nets (LLINs) impregnated with piperonyl butoxide reduced mosquito blood feeding more compared with conventional LLINs. On the other hand, we showed that few LLINs are maintained up to the end of their 3-year life span, and that older nets are less effective. These results support the policy change decisions by the Malawi National Malaria Control Program to switch from conventional LLINs to piperonyl butoxide LLINs, and to conduct mass LLIN distribution campaigns every 2 years. Our studies on epidemiological patterns of malaria infection showed that school-age children have higher malaria infection rates and lower use of control measures compared with younger children and adults. These findings added to the evidence base that influenced the National Malaria Control Program to endorse school-based malaria interventions as part of its national policy. Research supported by the Malawi ICEMR is contributing to in-country policy decisions and to the implementation of evidence-based interventions. Through our long-term studies we intend to continue providing practical and policy-relevant evidence necessary, ultimately, to eliminate malaria infection in Malawi.

Background Malaria vector control using insecticide-based approaches has proven to be an effective strategy. However, widespread insecticide resistance among malaria vector populations across sub-Saharan Africa threatens to derail control efforts. This study was conducted in Chikwawa district, an area in rural southern Malawi characterised by persistent malaria transmission and reports of insecticide resistance in the local mosquito population. The aim of the was to characterise the intensity of insecticide resistance within a population of Anopheles funestus sensu lato (s.l.), a major vector of malaria in this district. Methods Live adult females belonging to the An. funestus group were collected from households by indoor aspiration. The CDC bottle assay was used for phenotypic quantification of resistance to deltamethrin, permethrin and alpha-cypermethrin at 1×, 2.5×, 5× and 10× the recommended diagnostic dose for each of these insecticides. WHO tube assays were used to determine susceptibility to bendiocarb, dichlorodiphenyltrichloroethane (DDT) and pirimiphos-methyl insecticides at diagnostic concentrations. Results Anopheles funestus s.l. exposed to 10× the recommended diagnostic dose was highly resistant to alpha-cypermethrin (mortality 95.4%); in contrast, mortality was 100% when exposed to both deltamethrin and permethrin at the same dose. Despite showing susceptibility to deltamethrin and permethrin at the 10× concentration, mortality at the 5× concentration was 96.7% and 97.1%, respectively, indicating moderate resistance to these two insecticides. WHO susceptibility assays indicated strong resistance against bendiocarb (mortality 33.8%, n = 93), whereas there was full susceptibility to DDT (mortality 98.9%, n = 103) and pirimiphos-methyl (mortality 100%, n = 103). Conclusions Strategies for managing resistance to insecticides, particularly against pyrethroids, must be urgently implemented to maintain the effectiveness of insecticide-based vector control interventions in the area. Such strategies include the wide-scale introduction of third-generation synergist insecticide-treated bed nets (ITNs) and next-generation dual active ingredient ITNs. The use of effective non-pyrethroids, such as pirimiphos-methyl, clothianidin and potentially DDT, could provide a window of opportunity for indoor residual spraying across the district. This strategy would support the current Malawi Insecticide Resistance Management Plan which aims at rotating insecticides to minimise selection pressure and slow down the evolution of resistance to approved insecticides. These actions will help to prevent malaria vector control failure and improve progress towards malaria elimination. Graphical Abstract

Despite the scale-up of interventions against malaria over the past decade, this disease remains a leading threat to health in Malawi. To evaluate the epidemiology of both Plasmodium falciparum infection and malaria disease, the Malawi International Center of Excellence for Malaria Research (ICEMR) has developed and implemented diverse and robust surveillance and research projects. Descriptive studies in ICEMR Phase 1 increased our understanding of the declining effectiveness of long-lasting insecticidal nets (LLINs), the role of school-age children in malaria parasite transmission, and the complexity of host–parasite interactions leading to disease. These findings informed the design of ICEMR Phase 2 to test hypotheses about LLIN use and effectiveness, vector resistance to insecticides, demographic targets of malaria control, patterns and causes of asymptomatic to life-threatening disease, and the impacts of RTS,S vaccination plus piperonyl butoxide-treated LLINs on infection and disease in young children. These investigations are helping us to understand mosquito-to-human and human-to-mosquito transmission in the context of Malawi's intransigent malaria problem.

Background Access to human hosts by Anopheles mosquitoes is a key determinant of vectorial capacity for malaria, but it can be limited by use of long-lasting insecticidal nets (LLINs). In Malawi, pyrethroid-treated LLINs with and without the synergist piperonyl butoxide (PBO) were distributed to control malaria. This study investigated the blood-feeding patterns of malaria vectors and whether LLINs containing pyrethroid and PBO led to a reduction of human blood feeding than those containing only pyrethroids. Methods Mosquitoes were sampled inside houses from May 2019 through April 2020 by aspiration, pyrethrum spray catch, and light trap methods in two sites. One site (Namanolo, Balaka district) had LLINs containing only pyrethroids whereas the other (Ntaja, Machinga district) had LLINs with both pyrethroids and PBO. Anopheles species, their blood-meal host, and infection with Plasmodium falciparum were determined using PCR methods. Results A total of 6585 female Anopheles were sampled in 203 houses. Of these, 633 (9.6%) were blood-fed mosquitoes comprising of 279 (44.1%) Anopheles arabiensis, 103 (16.3%) Anopheles gambiae 212 (33.5), Anopheles funestus, 2 (0.3%), Anopheles parensis and 37 (5.8%) were unidentified Anopheles spp. Blood meal hosts were successfully identified for 85.5% (n = 541) of the blood-fed mosquitoes, of which 436 (81.0%) were human blood meals, 28 (5.2%) were goats, 11 (2.0%) were dogs, 60 (11.1%) were mixed goat-human blood meals, 5 (0.9%) were dog–human, and 1 was a mixed dog-goat. Human blood index (fraction of blood meals that were humans) was significantly higher in Namanolo (0.96) than Ntaja (0.89). Even though human blood index was high, goats were over-selected than humans after accounting for relative abundance of both hosts. The number of infectious Anopheles bites per person-year was 44 in Namanolo and 22 in Ntaja. Conclusion Although LLINs with PBO PBO may have reduced human blood feeding, access to humans was extremely high despite high LLIN ownership and usage rates in both sites. This finding could explain persistently high rates of malaria infections in Malawi. However, this study had one village for each net type, thus the observed differences may have been a result of other factors present in each village.

Background Understanding the blood feeding preferences and resting habits of malaria vectors is important for assessing and designing effective malaria vector control tools. The presence of livestock, such as cattle, which are used as blood meal hosts by some malaria vectors, may impact malaria parasite transmission dynamics. The presence of livestock may provide sufficient blood meals for the vectors, thereby reducing the frequency of vectors biting humans. Alternatively, the presence of cattle may enhance the availability of blood meals such that infectious mosquitoes may survive longer, thereby increasing the risk of malaria transmission. This study assessed the effect of household-level cattle presence and distribution on the abundance of indoor and outdoor resting malaria vectors. Methods Houses with and without cattle were selected in Chikwawa district, southern Malawi for sampling resting malaria vectors. Prokopack aspirators and clay pots were used for indoor and outdoor sampling, respectively. Each house was sampled over two consecutive days. For houses with cattle nearby, the number of cattle and the distances from the house to where the cattle were corralled the previous night were recorded. All data were analysed using generalized linear models fitted with Poisson distribution. Results The malaria vectors caught resting indoors were Anopheles gambiae sensustricto (s.s.), Anopheles arabiensis and Anopheles funestuss.s. Outdoor collections consisted primarily of An. arabiensis. The catch sizes of indoor resting An. gambiae sensulato (s.l.) were not different in houses with and without cattle (P = 0.34). The presence of cattle near a house was associated with a reduction in the abundance of indoor resting An. funestuss.l. (P = 0.04). This effect was strongest when cattle were kept overnight ≤ 15 m away from the houses (P = 0.03). The blood meal hosts varied across the species. Conclusion These results highlight differences between malaria vector species and their interactions with potential blood meal hosts, which may have implications for malaria risk. Whereas An. arabiensis remained unaffected, the reduction of An. funestuss.s. in houses near cattle suggests a potential protective effect of cattle. However, the low abundance of mosquitoes reduced the power of some analyses and limited the generalizability of the results to other settings. Therefore, further studies incorporating the vectors’ host-seeking behaviour/human biting rates are recommended to fully support the primary finding.

Background Current standard interventions are not universally sufficient for malaria elimination. The effects of community-based house improvement (HI) and larval source management (LSM) as supplementary interventions to the Malawi National Malaria Control Programme (NMCP) interventions were assessed in the context of an intensive community engagement programme. Methods The study was a two-by-two factorial, cluster-randomized controlled trial in Malawi. Village clusters were randomly assigned to four arms: a control arm; HI; LSM; and HI + LSM. Malawi NMCP interventions and community engagement were used in all arms. Household-level, cross-sectional surveys were conducted on a rolling, 2-monthly basis to measure parasitological and entomological outcomes over 3 years, beginning with one baseline year. The primary outcome was the entomological inoculation rate (EIR). Secondary outcomes included mosquito density, Plasmodium falciparum prevalence, and haemoglobin levels. All outcomes were assessed based on intention to treat, and comparisons between trial arms were conducted at both cluster and household level. Results Eighteen clusters derived from 53 villages with 4558 households and 20,013 people were randomly assigned to the four trial arms. The mean nightly EIR fell from 0.010 infectious bites per person (95% CI 0.006–0.015) in the baseline year to 0.001 (0.000, 0.003) in the last year of the trial. Over the full trial period, the EIR did not differ between the four trial arms (p = 0.33). Similar results were observed for the other outcomes: mosquito density and P. falciparum prevalence decreased over 3 years of sampling, while haemoglobin levels increased; and there were minimal differences between the trial arms during the trial period. Conclusions In the context of high insecticide-treated bed net use, neither community-based HI, LSM, nor HI + LSM contributed to further reductions in malaria transmission or prevalence beyond the reductions observed over two years across all four trial arms. This was the first trial, as far as the authors are aware, to test the potential complementary impact of LSM and/or HI beyond levels achieved by standard interventions. The unexpectedly low EIR values following intervention implementation indicated a promising reduction in malaria transmission for the area, but also limited the usefulness of this outcome for measuring differences in malaria transmission among the trial arms. Trial registration PACTR, PACTR201604001501493, Registered 3 March 2016, https://pactr.samrc.ac.za/.

Background: Monitoring malaria transmission is a critical component of efforts to achieve targets for elimination and eradication. Two commonly monitored metrics of transmission intensity are parasite prevalence (PR) and the entomological inoculation rate (EIR). Comparing the spatial and temporal variations in the PR and EIR of a given geographical region and modelling the relationship between the two metrics may provide a fuller picture of the malaria epidemiology of the region to inform control activities. Methods: Using geostatistical methods, we compare the spatial and temporal patterns of Plasmodium falciparum EIR and PR using data collected over 38 months in a rural area of Malawi. We then quantify the relationship between EIR and PR by using empirical and mechanistic statistical models. Results: Hotspots identified through the EIR and PR partly overlapped during high transmission seasons but not during low transmission seasons. The estimated relationship showed a 1-month delayed effect of EIR on PR such that at lower levels of EIR, increases in EIR are associated with rapid rise in PR, whereas at higher levels of EIR, changes in EIR do not translate into notable changes in PR. Conclusions: Our study emphasises the need for integrated malaria control strategies that combine vector and human host managements monitored by both entomological and parasitaemia indices. Funding: This work was supported by Stichting Dioraphte grant number 13050800.

Background Long-lasting insecticidal nets (LLINs) are the primary malaria prevention and control intervention in many parts of sub-Saharan Africa. While LLINs are expected to last at least 3 years under normal use conditions, they can lose effectiveness because they fall out of use, are discarded, repurposed, physically damaged, or lose insecticidal activity. The contributions of these different interrelated factors to durability of nets and their protection against malaria have been unclear. Methods Starting in 2009, LLIN durability studies were conducted in seven countries in Africa over 5 years. WHO-recommended measures of attrition, LLIN use, insecticidal activity, and physical integrity were recorded for eight different net brands. These data were combined with analyses of experimental hut data on feeding inhibition and killing effects of LLINs on both susceptible and pyrethroid resistant malaria vectors to estimate the protection against malaria transmission—in terms of vectorial capacity (VC)—provided by each net cohort over time. Impact on VC was then compared in hypothetical scenarios where one durability outcome measure was set at the best possible level while keeping the others at the observed levels. Results There was more variability in decay of protection over time by country than by net brand for three measures of durability (ratios of variance components 4.6, 4.4, and 1.8 times for LLIN survival, use, and integrity, respectively). In some countries, LLIN attrition was slow, but use declined rapidly. Non-use of LLINs generally had more effect on LLIN impact on VC than did attrition, hole formation, or insecticide loss. Conclusions There is much more variation in LLIN durability among countries than among net brands. Low levels of use may have a larger impact on effectiveness than does variation in attrition or LLIN degradation. The estimated entomological effects of chemical decay are relatively small, with physical decay probably more important as a driver of attrition and non-use than as a direct cause of loss of effect. Efforts to maximize LLIN impact in operational settings should focus on increasing LLIN usage, including through improvements in LLIN physical integrity. Further research is needed to understand household decisions related to LLIN use, including the influence of net durability and the presence of other nets in the household.

Assessing the biting behaviour of malaria vectors plays an integral role in understanding the dynamics of malaria transmission in a region. Biting times and preference for biting indoors or outdoors varies among mosquito species and across regions. These behaviours may also change over time in response to vector control measures such as long-lasting insecticidal nets (LLINs). Data on these parameters can provide the sites and times at which different interventions would be effective for vector control. This study assessed the biting patterns of malaria vectors in Chikwawa district, southern Malawi. The study was conducted during the dry and wet seasons in 2016 and 2017, respectively. In each season, mosquitoes were collected indoors and outdoors for 24 nights in six houses per night using the human landing catch. Volunteers were organized into six teams of two individuals, whereby three teams collected mosquitoes indoors and the other three collected mosquitoes outdoors each night, and the teams were rotated among twelve houses. All data were analyzed using Poisson log-linear models. The most abundant species were Anopheles gambiae sensu lato (primarily An. arabiensis) and An. funestus s.l. (exclusively An. funestus s.s.). During the dry season, the biting activity of An. gambiaes.l. was constant outdoors across the categorized hours (18:00 h to 08:45 h), but highest in the late evening hours (21:00 h to 23:45 h) during the wet season. The biting activity of An. funestus s.l. was highest in the late evening hours (21:00 h to 23:45 h) during the dry season and in the late night hours (03:00 h to 05:45 h) during the wet season. Whereas the number of An. funestuss.l. biting was constant (P = 0.662) in both seasons, that of An. gambiaes.l. was higher during the wet season than in the dry season (P = 0.001). Anopheles gambiae s.l. was more likely to bite outdoors than indoors in both seasons. During the wet season, An. funestus s.l. was more likely to bite indoors than outdoors but during the dry season, the bites were similar both indoors and outdoors. The biting activity that occurred in the early and late evening hours, both indoors and outdoors coincides with the times at which individuals may still be awake and physically active, and therefore unprotected by LLINs. Additionally, a substantial number of anopheline bites occurred outdoors. These findings imply that LLINs would only provide partial protection from malaria vectors, which would affect malaria transmission in this area. Therefore, protection against bites by malaria mosquitoes in the early and late evening hours is essential and can be achieved by designing interventions that reduce vector-host contacts during this period.

Introduction: Increasing the knowledgebase of anopheline larval ecology could enable targeted deployment of malaria control efforts and consequently reduce costs of implementation. In Malawi, there exists a knowledge gap in anopheline larval ecology and, therefore, basis for targeted deployment of larval source management (LSM) for malaria control, specifically larvicides. We set out to characterize anopheline larval habitats in the Majete area of Malawi on the basis of habitat ecology and anopheline larval productivity to create a basis for larval control initiatives in the country. Methods: Longitudinal surveys were conducted in randomly selected larval habitats over a period of fifteen months in Chikwawa district, southern Malawi. Biotic and abiotic parameters of the habitats were modelled to determine their effect on the occurrence and densities of anopheline larvae. Results: Seventy aquatic habitats were individually visited between 1-7 times over the study period. A total of 5,123 immature mosquitoes (3,359 anophelines, 1,497 culicines and 267 pupae) were collected. Anopheline and culicine larvae were observed in sympatry in aquatic habitats. Of the nine habitat types followed, dams, swamps, ponds, borehole runoffs and drainage channels were the five most productive habitat types for anopheline mosquitoes. Anopheline densities were higher in aquatic habitats with bare soil making up part of the surrounding land cover (p

Background Malaria is increasing in some recently urbanized areas that historically were considered lower risk. Understanding what drives urban transmission is hampered by inconsistencies in how “urban” contexts are defined. A dichotomized “urban–rural” approach, based on political boundaries may misclassify environments or fail to capture local drivers of risk. Small-scale agriculture in urban or peri-urban settings has been shown to be a major risk determinant. Methods Household-level Anopheles abundance patterns in and around Malawi’s commercial capital of Blantyre (~ 1.9 M pop.) were analysed. Clusters (N = 64) of five houses each located at 2.5 km intervals along eight transects radiating out from Blantyre city centre were sampled during rainy and dry seasons of 2015 and 2016. Mosquito densities were measured inside houses using aspirators to sample resting mosquitoes, and un-baited CDC light traps to sample host seeking mosquitoes. Results Of 38,895 mosquitoes captured, 91% were female and 87% were Culex spp. Anopheles females (N = 5058) were primarily captured in light traps (97%). Anopheles abundance was greater during rainy seasons. Anopheles funestus was more abundant than Anopheles arabiensis, but both were found on all transects, and had similar associations with environmental risk factors. Anopheles funestus and An. arabiensis females significantly increased with distance from the urban centre, but this trend was not consistent across all transects. Presence of small-scale agriculture was predictive of greater Anopheles spp. abundance, even after controlling for urbanicity, number of nets per person, number of under-5-year olds, years of education, and season. Conclusions This study revealed how small-scale agriculture along a rural-to-urban transition was associated with An. arabiensis and An. funestus indoor abundances, and that indoor Anopheles density can be high within Blantyre city limits, particularly where agriculture is present. Typical rural areas with lower house density and greater distance from urban centres reflected landscapes more suitable for Anopheles reproduction and house invasion. However, similar characteristics and elevated Anopheles abundances were also found around some houses within the city limits. Thus, dichotomous designations of “urban” or “rural” can obscure important heterogeneity in the landscape of Plasmodium transmission, suggesting the need for more nuanced assessment of urban malaria risk and prevention efforts.

Background Most people infected with malaria acquire the infection indoors from mosquito vectors that entered the house through open eaves, windows and doors. Structural house improvement (e.g. closed eaves and screened windows) is an established method of reducing mosquito entry. It could be complementary to other interventions such as insecticide-treated bed nets (ITNs) for malaria control because it covers and protects all individuals in a house equally. However, when implemented at a large scale, house improvement may not be employed optimally. It is therefore critical to assess whether partial house improvement will have any effect on mosquito house entry. We investigated the effect of partial and complete eave closure on the house-entry rates of malaria vectors and other mosquitoes in southern Malawi. Methods The study was conducted for 25 nights in May-June 2016. Twenty-five traditional houses were modified according to five treatments: fully closed eaves, three different levels of partially closed eaves, and open eaves. All houses had fully screened windows and closed doors. Host-seeking mosquitoes were sampled inside these houses using Centers for Disease Control and Prevention (CDC) light traps. The effect of open eaves versus partial or complete eave closure on the number of mosquitoes trapped inside the house was estimated using a generalized linear mixed model fitted with Poisson distribution and a log-link function. Results House entry by malaria vectors was 14-times higher in houses with fully open eaves compared to houses with fully closed eaves adjusting for wall-type, number of people that slept in the house the previous night, cooking locations and presence of livestock. Houses with four small openings had 9 times more malaria vectors compared to houses with fully closed eaves. The catches of culicine mosquitoes caught in houses with fully closed eaves were not different from those caught in houses with the other treatments. Conclusions Closed eaves resulted in fewer malaria vectors in houses, with differences depending on the degree of eave closure. The ability of malaria vectors to locate any remaining entry points on improved houses, as demonstrated here, suggests that quality control must be an important component of implementing house improvement as an intervention.The lack of effect on culicine mosquitoes in this study could reduce acceptance of house improvement, as implemented here, by household residents due to continued nuisance biting. This limitation could be addressed through community engagement (e.g. encouraging people to close their doors early in the evenings) or improved designs.

Indoor residual spraying and long-lasting insecticidal nets (LLINs) are key tools for malaria vector control. Malawi has struggled to scale up indoor residual spraying and to improve LLIN coverage and usage.In 2002, the Malawian National Malaria Control Programme developed guidelines for insecticide treated net distribution to reach the strategic target of at least 60% coverage of households with an LLIN. By 2005, the target coverage was 80% of households and the Global Fund financed the scale-up. The US President's Malaria Initiative funded the indoor residual spraying intervention.Malawi's entire population is considered to be at risk of malaria. Poor vector control, insecticide resistance in malaria vectors and insufficient technical and financial support have exacerbated the malaria burden.Between 2002 and 2012, 18 248 206 LLINs had been distributed. The coverage of at least one LLIN per household increased from 27% (3689/13 664) to 58% (1974/3404). Indoor residual spraying coverage increased from 28 227 to 653 592 structures between 2007 and 2011. However, vector resistance prompted a switch from pyrethroids to organophosphates for indoor residual spraying, which increased the cost and operations needed to be cut back from seven to one district. Malaria cases increased from 2 853 315 in 2002 to 6 748 535 in 2010, and thereafter dropped to 4 922 596 in 2012.A single intervention-based approach for vector control may have suboptimal impact. Well-coordinated integrated vector management may offer greater benefits. A resistance management plan is essential for effective and sustainable vector control.La pulvérisation d’insecticides à effet rémanent à l’intérieur des habitations et l'utilisation de moustiquaires à imprégnation durable (MID) sont des mesures clés dans la lutte antivectorielle contre le paludisme. Mais le Malawi a eu du mal à intensifier les interventions de pulvérisation intradomiciliaire d'insecticides et à améliorer la protection par des MID et leur utilisation.En 2002, le programme national de lutte contre le paludisme au Malawi a conçu des directives pour distribuer des moustiquaires imprégnées d'insecticides en vue d'atteindre l'objectif stratégique d'au moins 60% des ménages utilisant une MID. En 2005, la couverture ciblée est passée à 80% des ménages, et le Fonds mondial a financé l'intensification de la campagne. Les interventions de pulvérisation intradomiciliaire d'insecticides à effet rémanent ont été financées par l'Initiative du Président des États-Unis contre le paludisme.On considère que l'intégralité de la population du Malawi est exposée au risque palustre. Mais une lutte antivectorielle déficiente, le développement d'une résistance aux insecticides chez les vecteurs du paludisme et un soutien technique et financier insuffisant ont aggravé la charge du paludisme.Entre 2002 et 2012, 18 248 206 MID ont été distribuées. L'utilisation d'au moins une MID dans chaque ménage est passée de 27% (3 689/13 664) à 58% (1 974/3 404). La couverture par pulvérisation intradomiciliaire à effet rémanent est passée de 28 227 à 653 592 structures entre 2007 et 2011. Néanmoins, la résistance des vecteurs aux insecticides a nécessité d'abandonner les pyréthrinoïdes au profit des organophosphorés pour les pulvérisations intradomiciliaires, ce qui a majoré les coûts et nécessité de limiter les interventions à un seul district, sur les sept initialement prévus. Les cas de paludisme ont augmenté de 2 853 315 en 2002 à 6 748 535 en 2010 avant de chuter à 4 922 596 en 2012.En matière de lutte antivectorielle, une approche fondée sur un seul type d'intervention peut avoir des effets sous-optimaux. Une gestion antivectorielle intégrée correctement coordonnée pourrait être plus bénéfique. Un plan de gestion de la résistance est essentiel pour une lutte antivectorielle efficace et durable.La fumigación de interiores con acción residual y los mosquiteros tratados con insecticidas de larga duración (LLIN, por sus siglas en inglés) son herramientas importantes para el control de vectores de la malaria. Malawi ha luchado por aumentar la fumigación de interiores con acción residual y por mejorar la cobertura y uso de los LLIN.En 2002, el Programa de Control Nacional contra la Malaria de Malawi desarrolló directrices para la distribución de mosquiteros tratados con insecticidas con el fin de alcanzar el objetivo estratégico de que como mínimo el 60% de los hogares dispusieran de un LLIN. En 2005, la cobertura objetivo era un 80% de los hogares y el Fondo Mundial financió la ampliación. La Iniciativa del Presidente de los Estados Unidos de América contra la Malaria financió la intervención de la fumigación de interiores con acción residual.Se considera que toda la población de Malawi corre el riesgo de sufrir malaria. Los escasos controles de vectores, la resistencia de los insecticidas en los vectores de la malaria y el apoyo técnico y financiero insuficiente han multiplicado las tasas de malaria.Entre 2002 y 2012, se han distribuido 18 248 206 LLIN. La cobertura de al menos un LLIN por hogar ha aumentado de un 27% (3 689/13 664) a un 58% (1 974/3 404). La cobertura de fumigación de interiores con acción residual ha aumentado de 28 227 a 653 592 estructuras entre 2007 y 2011. No obstante, la resistencia de vectores ha acelerado un cambio de piretroides a organofosfatos para la fumigación de interiores con acción residual, lo que ha aumentado el coste y las operaciones necesarias para reducir de siete distritos a uno. Los casos de malaria aumentaron de 2 853 315 en 2002 a 6 748 535 en 2010, y luego cayeron a 4 922 596 en 2012.Un enfoque basado en una única intervención para el control de vectores puede tener un impacto subóptimo. Una gestión integrada de vectores bien coordinada puede ofrecer mayores beneficios. Es fundamental desarrollar un plan de gestión de resistencia para lograr un control de vectores eficaz y sostenible.تتمثل الوسائل الرئيسية لمكافحة ناقلات مرض الملاريا في رش الأماكن المغلقة بمبيدات حشرية تدوم طويلاً واستعمال الناموسيات المعالجة بمبيدات حشرية مديدة المفعول (LLIN). ناضلت ملاوي من أجل زيادة معدل رش الأماكن المغلقة بمبيدات حشرية تدوم طويلاً لتحسين مدى توفير الناموسيات من نوع LLIN واستعمالها.تم العمل في عام 2002 بالبرنامج الوطني لمكافحة الملاريا في ملاوي على وضع مبادئ توجيهية لتوزيع الناموسية المعالجة بمبيد حشري سعيًا إلى تحقيق الهدف الاستراتيجي الرامي إلى توفير الناموسيات بما يغطي 60‏% على الأقل من الدور. وبلغت نسبة التغطية 80% من الدُور مع حلول عام 2005، وقد قدّم الصندوق العالمي التمويل اللازم لرفع تلك النسبة. ووفرت مبادرة الرئيس الأمريكي لمكافحة الملاريا التمويل اللازم لتنفيذ التدخل المتعلق برش الأماكن المغلقة بمبيدات حشرية تدوم طويلاً.تم اعتبار سكان ملاوي بأكملهم من المعرضين لخطر الإصابة بمرض الملاريا، فقد أدى انخفاض مستوى مكافحة ناقلات المرض، ومقاومة ناقلات مرض الملاريا للمبيدات الحشرية، ونقص الدعم المالي والتقني إلى تفاقم عبء مرض الملاريا.تم توزيع 18,248,206 من الناموسيات من نوع LLIN في الفترة بين عامي 2002 و2012. وقد ارتفع مستوى التغطية التي تهدف إلى توفير ناموسية واحدة على الأقل من نوع LLIN لكل منزل من 27‏% (3689/13,664) ليصل 58‏% (1974/3404). كما ارتفع مستوى التغطية التي تهدف إلى رش الأماكن المغلقة بمبيدات حشرية تدوم طويلاً من 28,227 منشأة ليصل إلى 653,592 منشأة في الفترة بين عامي 2007 و2011. وبالرغم من ذلك، كانت مقاومة ناقلات المرض للمبيدات دافعًا للتحول من استخدام مادة بيريثرويد إلى المركبات الفوسفاتية العضوية فيما يتعلق برش الأماكن المغلقة بمبيدات حشرية تدوم طويلاً، مما أدى إلى ارتفاع التكلفة وزيادة الإجراءات الواجب تقليلها من سبع مناطق ليقتصر على منطقة واحدة. وزادت حالات الإصابة بمرض الملاريا من 2,853,315 حالة في عام 2002 لتصل إلى 6,748,535 حالة في عام 2010، ومنذ ذلك الحين انخفض عدد الحالات ليصل إلى 4,922,596 حالة في عام 2012.إن اتباع أسلوب يعتمد على تدخل واحد لمكافحة ناقلات المرض قد يكون أثره دون الحد الأمثل. وقد تحقق الإدارة المتعلقة بناقلات المرض والتي تتسم بالتكامل وحسن التنسيق المزيد من المنافع. كما أن توفر خطة لإدارة مقاومة المبيدات أمر ضروري لتحقيق المكافحة الفعالة والمستمرة لناقلات المرض.室内滞留喷剂和长效驱虫蚊帐 (LLIN) 是控制疟疾媒介的重要工具。马拉维在推广室内滞留喷剂和提高长效驱虫蚊帐 (LLIN) 覆盖面和使用率方面困难重重。.2002 年，马拉维全国疟疾防治方案制定了一份指南，指导分发经过杀虫剂处理的蚊帐，以实现至少 60% 的住户拥有长效驱虫蚊帐 (LLIN) 的战略目标。到 2005 年，覆盖率目标为 80% 的住户，并且推广资金由全球基金会出资。 室内滞留喷剂干预由美国总统防治疟疾行动计划出资。.马拉维全体人口均面临疟疾的威胁。媒介控制水平差、疟疾媒介的抗药性以及技术和财政支持不足使得疟疾问题雪上加霜。.2002 年到 2012 之间，共分发了 18,248,206 件长效驱虫蚊帐 (LLIN)。每户至少一件长效驱虫蚊帐 (LLIN) 的覆盖率从 27% (3689/13 664) 增加到 58% (1974/3404)。2007 年到 2011 年之间，室内滞留喷剂覆盖率从 28, 227 户增加到 653, 592 户。但是，由于媒介的抗药性，必须使用有机磷酸酯类杀虫剂代替拟除虫菊酯进行室内滞留喷洒，这使得原计划用于 7 个地区的成本和运营减少至只能用于 1 个地区。从 2002 年到 2010 年，疟疾病例从 2,853,315 例增加到 6,748,535 例，然后，在 2012 年，降至 4,922,596 例。.单一的干预式媒介控制方法效果可能并不理想。相互协调的综合性媒介管理可能会取得更好的效果。抗药性管理计划是有效且可持续媒介控制的重中之重。.Остаточное распыление инсектицидов в помещении и инсектицидные сетки длительного действия (ИСДД) являются основными способами борьбы с переносчиками малярии. В Малави были предприняты упорные попытки расширить масштаб применения остаточного распыления инсектицидов и улучшить охват населения ИССД и показатели их использования.В 2002 году Национальной программой Малави по борьбе с малярией были разработаны рекомендации по распространению сеток, обработанных инсектицидами, для достижения стратегической цели — как минимум 60%-го охвата домашних хозяйств ИСДД. К 2005 году программа ставила целью уже 80%-й охват и Глобальный фонд профинансировал такое расширение. Инициатива президента США по борьбе с малярией выделила средства на остаточное распыление инсектицидов в помещениях.Считается, что все население Малави входит в группу риска в отношении заболевания малярией. По причине неудовлетворительных результатов борьбы с переносчиками, устойчивости переносчиков малярии к инсектицидам и недостаточной технической и финансовой поддержки бремя малярии усилилось.В период с 2002 по 2012 год было распространено 18 248 206 ИСДД. Охват населения (по меньшей мере одной ИСДД на домашнее хозяйство) вырос с 27% (3689 из 13 664 домохозяйств) до 58% (1974 из 3404 домохозяйств). Число опрыскиваемых помещений возросло с 28 227 до 653 592 в период с 2007 по 2011 год. Однако устойчивость, выработанная переносчиками, обусловила необходимость использовать для остаточного распыления органофосфаты вместо пиретроидов, из-за чего увеличилась стоимость обработки и охват соответствующими операциями пришлось сократить с семи округов до одного. Число случаев заболевания малярией выросло с 2 853 315 в 2002 году до 6 748 535 в 2010 году. Затем это количество сократилось до 4 922 596 случаев в 2012 году.Подход к борьбе с переносчиками заболевания, основанный на одном способе вмешательства, возможно, не позволил добиться оптимального эффекта. Большую пользу могут принести качественно скоординированные мероприятия по комплексной борьбе с переносчиками заболевания. Для эффективной и устойчивой борьбы с переносчиками заболевания необходим план противодействия устойчивости к инсектицидам.

Although urban malaria transmission is low and seasonal, it remains a major public health problem. This study aimed at demonstrating the presence ofTwo cross-sectional surveys were carried out in Blantyre District, Malawi, during the dry and wet seasons of 2008 and 2010, respectively. A map of Blantyre was divided into a grid of 400 cells, of which 60 cells were randomly selected. Five households located within 100 m from the centre of each selected cell were enrolled, a standard questionnaire was administered, and indoor resting mosquitoes were sampled.In 2008 and 2010, a total of 960 and 1045 mosquitoes were collected, respectively.The presence of

Background Due to outdoor and residual transmission and insecticide resistance, long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS) will be insufficient as stand-alone malaria vector control interventions in many settings as programmes shift toward malaria elimination. Combining additional vector control interventions as part of an integrated strategy would potentially overcome these challenges. Larval source management (LSM) and structural house improvements (HI) are appealing as additional components of an integrated vector management plan because of their long histories of use, evidence on effectiveness in appropriate settings, and unique modes of action compared to LLINs and IRS. Implementation of LSM and HI through a community-based approach could provide a path for rolling-out these interventions sustainably and on a large scale. Methods/design We will implement community-based LSM and HI, as additional interventions to the current national malaria control strategies, using a randomised block, 2 × 2 factorial, cluster-randomised design in rural, southern Malawi. These interventions will be continued for two years. The trial catchment area covers about 25,000 people living in 65 villages. Community participation is encouraged by training community volunteers as health animators, and supporting the organisation of village-level committees in collaboration with The Hunger Project, a non-governmental organisation. Household-level cross-sectional surveys, including parasitological and entomological sampling, will be conducted on a rolling, 2-monthly schedule to measure outcomes over two years (2016 to 2018). Coverage of LSM and HI will also be assessed throughout the trial area. Discussion Combining LSM and/or HI together with the interventions currently implemented by the Malawi National Malaria Control Programme is anticipated to reduce malaria transmission below the level reached by current interventions alone. Implementation of LSM and HI through a community-based approach provides an opportunity for optimum adaptation to the local ecological and social setting, and enhances the potential for sustainability. Trial Registration Registered with The Pan African Clinical Trials Registry on 3 March 2016, trial number PACTR201604001501493. Electronic supplementary material The online version of this article (10.1186/s12879-017-2749-2) contains supplementary material, which is available to authorized users.

Objective To quantify the geographical extent of filariasis and malaria control interventions impacting lymphatic filariasis (LF) in Malawi and to produce a multiple intervention score map (MISM) for prioritising surveillance and intervention strategies. Methods Interventions included mass drug administration (MDA) for LF and onchocerciasis, and bed nets and indoor residual spraying (IRS) for malaria. District and subdistrict-level data were obtained from the Ministry of Health in Malawi, the Demographic and Health Survey (DHS) and President's Malaria Initiative reports. Single intervention scores were calculated for each variable based on population coverage thresholds, and these were combined in a weighted sum to form a multiple intervention score, which was then used to produce maps, that is MISMs. Districts were further classified into four groups based on the combination of their baseline LF prevalence and multiple intervention score. Results The district- and subdistrict-level MISMs highlighted specific areas that have received high and low coverage of LF-impacting interventions. High coverage areas included the LF-onchocerciasis endemic areas in the southern region of the country and areas along the shores of Lake Malawi, where malaria vector control had been prioritised. Three districts with high baseline LF prevalence measures but low coverage of multiple interventions were identified and considered to be most at risk of ongoing transmission or re-emergence. Conclusions These maps and district classifications will be used by LF programme managers to identify and target high-risk areas that may not have received adequate LF-impacting interventions to interrupt the transmission of the disease.

Resistance to pyrethroids, the sole insecticide class recommended for treating bed nets, threatens the control of major malaria vectors, including Anopheles funestus Effective management of resistance requires an understanding of the dynamics and mechanisms driving resistance. Here, using genome-wide transcription and genetic diversity analyses, we show that a shift in the molecular basis of pyrethroid resistance in southern African populations of this species is associated with a restricted gene flow. Across the most highly endemic and densely populated regions in Malawi, An. funestus is resistant to pyrethroids, carbamates, and organochlorides. Genome-wide microarray-based transcription analysis identified overexpression of cytochrome P450 genes as the main mechanism driving this resistance. The most up-regulated genes include cytochrome P450s (CYP) CYP6P9a, CYP6P9b and CYP6M7. However, a significant shift in the overexpression profile of these genes was detected across a south/north transect, with CYP6P9a and CYP6P9b more highly overexpressed in the southern resistance front and CYP6M7 predominant in the northern front. A genome-wide genetic structure analysis of southern African populations of An. funestus from Zambia, Malawi, and Mozambique revealed a restriction of gene flow between populations, in line with the geographical variation observed in the transcriptomic analysis. Genetic polymorphism analysis of the three key resistance genes, CYP6P9a, CYP6P9b, and CYP6M7, support barriers to gene flow that are shaping the underlying molecular basis of pyrethroid resistance across southern Africa. This barrier to gene flow is likely to impact the design and implementation of resistance management strategies in the region.

Background Although malaria disease in urban and peri-urban areas of sub-Saharan Africa is a growing concern, the epidemiologic patterns and drivers of transmission in these settings remain poorly understood. Factors associated with variation in malaria risk in urban and peri-urban areas were evaluated in this study. Methods A health facility-based, age and location-matched, case–control study of children 6–59 months of age was conducted in four urban and two peri-urban health facilities (HF) of Blantyre city, Malawi. Children with fever who sought care from the same HF were tested for malaria parasites by microscopy and PCR. Those testing positive or negative on both were defined as malaria cases or controls, respectively. Results A total of 187 cases and 286 controls were studied. In univariate analyses, higher level of education, possession of TV, and electricity in the house were negatively associated with malaria illness; these associations were similar in urban and peri-urban zones. Having travelled in the month before testing was strongly associated with clinical malaria, but only for participants living in the urban zones (OR = 5.1; 95% CI = 1.62, 15.8). Use of long-lasting insecticide nets (LLINs) the previous night was not associated with protection from malaria disease in any setting. In multivariate analyses, electricity in the house, travel within the previous month, and a higher level of education were all associated with decreased odds of malaria disease. Only a limited number of Anopheles mosquitoes were found by aspiration inside the households in the peri-urban areas, and none was collected from the urban households. Conclusion Travel was the main factor influencing the incidence of malaria illness among residents of urban Blantyre compared with peri-urban areas. Identification and understanding of key mobile demographic groups, their behaviours, and the pattern of parasite dispersal is critical to the design of more targeted interventions for the urban setting. Electronic supplementary material The online version of this article (doi:10.1186/s12936-016-1623-9) contains supplementary material, which is available to authorized users.

The impact of insecticide resistance on insect-borne disease programs is difficult to quantify. The possibility of eliminating malaria in high-transmission settings is heavily dependent on effective vector control reducing disease transmission rates. Pyrethroids are the dominant insecticides used for malaria control, with few options for their replacement. Their failure will adversely affect our ability to control malaria. Pyrethroid resistance has been selected in Malawi over the last 3 y in the two major malaria vectors Anopheles gambiae and Anopheles funestus , with a higher frequency of resistance in the latter. The resistance in An. funestus is metabolically based and involves the up-regulation of two duplicated P450s. The same genes confer resistance in Mozambican An. funestus , although the levels of up-regulation differ. The selection of resistance over 3 y has not increased malaria transmission, as judged by annual point prevalence surveys in 1- to 4-y-old children. This is true in areas with long-lasting insecticide-treated nets (LLINs) alone or LLINs plus pyrethroid-based insecticide residual spraying (IRS). However, in districts where IRS was scaled up, it did not produce the expected decrease in malaria prevalence. As resistance increases in frequency from this low initial level, there is the potential for vector population numbers to increase with a concomitant negative impact on control efficacy. This should be monitored carefully as part of the operational activities in country.

Little is known about the impact of indoor residual spraying (IRS) in areas with intense malaria transmis- sion such as sub-Saharan Africa. In Malawi, IRS with lambda-cyhalothrin has been applied annually in an area of intense year-long transmission since 2007. We evaluated the impact of IRS on parasitemia and anemia prevalence in children less than five years of age by using a cross-sectional household survey conducted in 2009, six months after the second IRS spray round. We measured malaria parasitemia and anemia (hemoglobin level < 11 g/dL) in 899 children less than five years of age and used binomial regression to assess the impact of IRS by comparing children living in a household sprayed with IRS (direct IRS) with those in a household not sprayed with IRS, but in an IRS area (indirect IRS) and those living in a household not sprayed with IRS and not in an IRS area (no IRS). In the IRS area, 77% of households reported receiving IRS. Adjusting for bed net use, house construction, and socioeconomic status, we found that receiving direct IRS and indirect IRS were significantly associated with a 33% (95% confidence interval (CI) = 1-54%) and 46% (95% CI = 20-64%) reduction in parasitemia and a 21% (95% CI = 4-34%) and 30% (95% CI = 12-45%) reduction in anemia prevalence, respectively.

Background Deciphering the dynamics and evolution of insecticide resistance in malaria vectors is crucial for successful vector control. This study reports an increase of resistance intensity and a rise of multiple insecticide resistance in Anopheles funestus in Malawi leading to reduced bed net efficacy. Methods Anopheles funestus group mosquitoes were collected in southern Malawi and the species composition, Plasmodium infection rate, susceptibility to insecticides and molecular bases of the resistance were analysed. Results Mosquito collection revealed a predominance of An. funestus group mosquitoes with a high hybrid rate (12.2 %) suggesting extensive species hybridization. An. funestus sensu stricto was the main Plasmodium vector (4.8 % infection). Consistently high levels of resistance to pyrethroid and carbamate insecticides were recorded and had increased between 2009 and 2014. Furthermore, the 2014 collection exhibited multiple insecticide resistance, notably to DDT, contrary to 2009. Increased pyrethroid resistance correlates with reduced efficacy of bed nets (

Background Although urban malaria transmission is low and seasonal, it remains a major public health problem. This study aimed at demonstrating the presence of Anopheles mosquitoes and their potential to transmit malaria in urban settings. Methods Two cross-sectional surveys were carried out in Blantyre District, Malawi, during the dry and wet seasons of 2008 and 2010, respectively. A map of Blantyre was divided into a grid of 400 cells, of which 60 cells were randomly selected. Five households located within 100 m from the centre of each selected cell were enrolled, a standard questionnaire was administered, and indoor resting mosquitoes were sampled. Results In 2008 and 2010, a total of 960 and 1045 mosquitoes were collected, respectively. Anopheles funestus comprised 9.9% (n = 95) and 10.3% (n = 108) during the two surveys, respectively. Anopheles gambiae sensu lato (s.l.) was rarely detected during the second survey (n = 6; 0.6%). Molecular identification was performed on samples collected during the first survey, and An. funestus sensu stricto (s.s.) was the only sibling species detected. All the Anopheles mosquitoes were collected from households located in rural areas of Blantyre and none from urban areas. In univariate analysis, the presence of open eaves was associated with increased Anopheles prevalence, both during the dry (incidence rate ratio, IRR = 4.3; 95% CI 2.4 – 7.6) and wet (IRR = 2.47; 95% CI 1.7 – 3.59) seasons. Chances of detecting Anopheles spp. decreased with increasing altitude (IRR = 0.996; 95% CI 0.995 – 0.997) and during the dry season, but increased during the wet season (IRR = 1.0017; 95% CI 1.0012 – 1.0023). These factors remained significant following a multiple Poisson regression analysis. No association was found between insecticide-treated bednet ownership and the number of Anopheles mosquitoes detected. Conclusions The presence of An. funestus s.s and An. gambiae s.l. in the periphery of Blantyre city was an indication that malaria transmission was potentially taking place in these areas.

Background Although malaria is highly prevalent throughout Malawi, little is known of its transmission dynamics. This paper describes the seasonal activity of the different vectors, human biting indices, sporozoite rates and the entomological inoculation rate in a low-lying rural area in southern Malawi. Methods Vectors were sampled over 52 weeks from January 2002 to January 2003, by pyrethrum knockdown catch in two villages in Chikhwawa district, in the Lower Shire Valley. Results In total, 7,717 anophelines were collected of which 55.1% were Anopheles gambiae sensu lato and 44.9% were Anopheles funestus. Three members of the An. gambiae complex were identified by PCR: Anopheles arabiensis (75%) was abundant throughout the year, An. gambiae s.s. (25%) was most common during the wet season and Anopheles quadriannulatus occurred at a very low frequency (n=16). An. funestus was found in all samples but was most common during the dry season. Anopheles gambiae s.s. and An. funestus were highly anthropophilic with human blood indices of 99.2% and 96.3%, respectively. Anopheles arabiensis had fed predominantly on humans (85.0%) and less commonly on cattle (10.9%; 1.2% of blood meals were of mixed origin). Plasmodium falciparum (192/3,984) and Plasmodium malariae (1/3,984) sporozoites were detected by PCR in An. arabiensis (3.2%) and An. funestus (4.5%), and in a significantly higher proportion of An. gambiae s.s. (10.6%)(pP. falciparum sporozoite rate was 4.8%, resulting in estimated inoculation rates of 183 infective bites/ person per annum, or an average rate of ~15 infective bites/person/month. Conclusions The results demonstrate the importance of An. gambiae s.s., An. arabiensis and An. funestus in driving the high levels of malaria transmission in the south of Malawi. Sustained and high coverage or roll out of current approaches to malaria control (primarily insecticide-treated bed nets and indoor residual house spraying) in the area are likely to reduce the observed high malaria transmission rate and consequently the incidence of human infections, unless impeded by increasing resistance of vectors to insecticides.

Background\ud \ud Insecticide treated nets (ITN) and indoor residual spraying (IRS) are the two pillars of malaria vector control in Africa, but both interventions are beset by quality and coverage concerns. Data from three control programs were used to investigate the impact of: 1) the physical deterioration of ITNs, and 2) inadequate IRS spray coverage, on their respective protective effectiveness.\ud \ud Methods\ud \ud Malaria indicator surveys were carried out in 2009 and 2010 in Bioko Island, mainland Equatorial Guinea and Malawi to monitor infection with P.falciparum in children, mosquito net use, net condition and spray status of houses. Nets were classified by their condition. The association between infection and quality and coverage of interventions was investigated.\ud \ud Results\ud \ud There was reduced odds of infection with P.falciparum in children sleeping under ITNs that were intact (Odds ratio (OR): 0.65, 95% CI: 0.55–0.77 and OR: 0.81, 95% CI: 0.56–1.18 in Equatorial Guinea and in Malawi respectively), but the protective effect became less with increasingly worse condition of the net. There was evidence for a linear trend in infection per category increase in deterioration of nets. In Equatorial Guinea IRS offered protection to those in sprayed and unsprayed houses alike when neighbourhood spray coverage was high (≥80%) compared to those living in areas of low IRS coverage (

Malaria control in the impoverished, highly endemic settings of sub-Saharan Africa remains a major public health challenge. Successes have been achieved only where sustained, concerted, multi-pronged interventions have been instituted. As one of the world’s poorest countries, Malawi experiences malaria incidence rates that have remained high despite a decade of gradually expanding and more intensive prevention efforts. The Malawi International Center for Excellence in Malaria Research (ICEMR) is beginning work to augment the knowledge base for reducing Plasmodium transmission and malaria morbidity and mortality. Among ICEMR goals, we intend to better assess patterns of infection and disease, and analyze transmission by Anopheles vector species in both urban and rural ecological settings. We will evaluate parasite population genetics and dynamics, transmission intensities and vector ecologies, social and environmental determinants of disease patterns and risk, and human-vector-parasite dynamics. Such context-specific information will help to focus appropriate prevention and treatment activities on efforts to control malaria in Malawi. In zones of intense and stable transmission, like Malawi,, elimination poses particularly thorny challenges - - and these challengers are different from those of traditional control and prevention activities. Working toward elimination will require knowledge of how various interventions impact on transmission as it approaches very low levels. At present, Malawi is faced with immediate, context-specific problems of scaling-up prevention and control activities simply to begin reducing infection and disease to tolerable levels. The research required to support these objectives is critically evaluated here.

The population genetics and structure of P. falciparum determine the rate at which malaria evolves in response to interventions such as drugs and vaccines. This has been the source of considerable recent controversy, but here we demonstrate the organism to be essentially sexual, in an area of moderately high transmission in the Lower Shire Valley, Malawi. Seven thousand mosquitoes were collected and dissected, and genetic data were obtained on 190 oocysts from 56 infected midguts. The oocysts were genotyped at three microsatellite loci and the MSP1 locus. Selfing rate was estimated as 50% and there was significant genotypic linkage disequilibrium (LD) in the pooled oocysts. A more appropriate analysis searching for genotypic LD in outcrossed oocysts and/or haplotypic LD in the selfed oocysts found no evidence for LD, indicating that the population was effectively sexual. Inbreeding estimates at MSP1 were higher than at the microsatellites, possibly indicative of immune action against MSP1, but the effect was confounded by the probable presence of null mutations. Mating appeared to occur at random in mosquitoes and evidence regarding whether malaria clones in the same host were related (presumably through simultaneous inoculation in the same mosquito bite) was ambiguous. This is the most detailed genetic analysis yet of P. falciparum sexual stages, and shows P. falciparum to be a sexual organism whose genomes are in linkage equilibrium, which acts to slow the emergence of drug resistance and vaccine insensitivity, extending the likely useful therapeutic lifespan of drugs and vaccines.

Background Insecticide-treated bed nets (ITNs) are the cornerstone of malaria control in sub-Saharan Africa but their effectiveness may be compromised by the spread of pyrethroid resistance among malaria vectors. The objective of this investigation was to assess the effectiveness of ITNs to prevent malaria in an area of Malawi with moderate pyrethroid resistance. Methods One deltamethrin ITN was distributed in the study area for every two individuals in each household plus one extra ITN for households with an odd number of residents. A fixed cohort of 1,199 children aged six to 59 months was seen monthly for one year and at sick visits to measure malaria infection and use of ITNs. Insecticide resistance among malaria vectors was measured. The effect of ITN use on malaria incidence was assessed, adjusting for potential confounders using generalized estimating equations accounting for repeated measures. Results There were 1,909 infections with Plasmodium falciparum over 905 person-years at risk (PYAR), resulting in an observed incidence of 2.1 infections per person-year (iPPY). ITNs were used during 97% of the PYAR. The main vector was Anopheles funestus: mortality in WHO tube assays after exposure to 0.05% deltamethrin was 38% (95% confidence interval (CI) 29–47), and resistance was due to elevated oxidase enzymes. After adjusting for potential confounders, the incidence of malaria infection among ITN users was 1.7 iPPY (95% CI 1.5-2.1) and among non-bed net users was 2.6 iPPY (95% CI 2.0-3.3). Use of ITNs reduced the incidence of malaria infection by 30% (rate ratio 0.7; 95% CI, 0.5-0.8) compared to no bed nets. Conclusion ITNs significantly reduced the incidence of malaria infection in children in an area with moderate levels of pyrethroid resistance and considerable malaria transmission. This is the first study to show that ITNs provide protection in areas where pyrethroid-resistant An. funestus is the major malaria vector. Malaria control programmes should continue to distribute and promote ITNs in areas with low to moderate pyrethroid resistance; however, insecticide resistance may intensify further and it is not known whether ITNs will remain effective at higher levels of resistance. There is an urgent need to identify or develop new insecticides and technologies to limit the vulnerability of ITNs to insecticide resistance.