Bed Net Coverage Research Articles

Impact of increased ventilation on indoor temperature and malaria mosquito density: an experimental study in The Gambia.

In sub-Saharan Africa, cooler houses would increase the coverage of insecticide-treated bednets, the primary malaria control tool. We examined whether improved ventilation, using windows screened with netting, cools houses at night and reduces malaria mosquito house entry in The Gambia. Identical houses were constructed, with badly fitting doors the only mosquito entry points. Two men slept in each house and mosquitoes captured using light traps. First, temperature and mosquito density were compared in four houses with 0, 1, 2 and 3 screened windows. Second, carbon dioxide (CO2), a major mosquito attractant, was measured in houses with (i) no windows, (ii) screened windows and (iii) screened windows and screened doors. Computational fluid dynamic modelling captured the spatial movement of CO2. Increasing ventilation made houses cooler, more comfortable and reduced malaria mosquito house entry; with three windows reducing mosquito densities by 95% (95%CI = 90–98%). Screened windows and doors reduced the indoor temperature by 0.6°C (95%CI = 0.5–0.7°C), indoor CO2 concentrations by 31% between 21.00 and 00.00 h and malaria mosquito entry by 76% (95%CI = 69–82%). Modelling shows screening reduces CO2 plumes from houses. Under our experimental conditions, cross-ventilation not only reduced indoor temperature, but reduced the density of house-entering malaria mosquitoes, by weakening CO2 plumes emanating from houses.

A Decline and Age Shift in Malaria Incidence in Rural Mali following Implementation of Seasonal Malaria Chemoprevention and Indoor Residual Spraying.

ABSTRACTMany African countries have reported declines in malaria incidence, attributed to the implementation of control strategies. In Mali, artemisinin-based combination therapy (ACT) was introduced in 2004, and long-lasting insecticide-treated nets (LLINs) have been partially distributed free of charge since 2007. In the Malian town of Bandiagara, a study conducted from 2009 to 2013 showed a stable incidence of malaria compared with 1999, despite the implementation of ACTs and LLINs. Since 2016, seasonal malaria chemoprevention has been scaled up across the country. In addition to these strategies, the population of Bandiagara benefited from indoor residual spray implementation in 2017 and 2018 and continued universal bed net coverage. This study aimed to measure the incidence of malaria in Bandiagara, given this recent scaling up of control strategies. A cohort of 300 children aged 6 months to 15 years was followed up from October 2017 to December 2018. We performed monthly cross-sectional surveys to measure anemia and the prevalence of malaria infection by microscopy. The overall incidence of symptomatic malaria was 0.5 episodes/person-year. Malaria incidence in children up to 5 years old significantly declined since 2012 and since 1999 (incidence rate ratio estimates: 6.7 [95% CI: 4.2–11.4] and 13.5 [95% CI: 8.4–22.7]), respectively. The average prevalence of malaria parasitemia was 6.7%. Malaria incidence was higher in children older than 5 years than in those younger than 5 years, highlighting the need to extend malaria control efforts to these older children.

Quantifying the impact of insecticide resistance in the transmission dynamics of malaria

Abstract The fitness cost imposed by insecticide resistance on malaria vectors has appeared as an asset for vector control despite the evolution and spread of insecticide resistance. However, certain levels of insecticide resistance intensity may reduce the efficacy of insecticide-treated nets for certain coverage levels. In this study, we consider a non-autonomous mathematical model for malaria transmission that investigates the impact of the interaction between the intensity of resistance, the coverage of insecticide-treated nets and the fitness cost of resistance on resistant vectors (fitness disadvantage or decreased performance) on the transmission dynamics of malaria. It is shown that the disease-free periodic solution of the model is globally attractive if the time-dependent reproduction number ( R T ( t ) 1 ). The model also admits a unique positive periodic solution when R T ( t ) > 1 . We numerically studied the interaction between the fitness cost imposed by resistance on resistant vectors, the intensity of resistance and bed-net coverage. We observed that the intensity level present in the population may significantly affect the impact of the fitness cost that resistance imposes on resistant mosquitoes as well as reduce the effectiveness of control measures.

IMPACT OF ADAPTIVE MOSQUITO BEHAVIOR AND INSECTICIDE-TREATED NETS ON MALARIA PREVALENCE

Malaria prevalence in sub-Saharan Africa remains high. Kenya for example, records about 3.5 million new cases and 11 thousand deaths each year.1 Most of these cases and deaths are among children under five. The main control method in malaria endemic regions has been through the use of insecticide-treated nets (ITNs). Although this approach has been fairly successful, the gains are threatened by mosquito-resistance to pyrethroids (insecticides on nets), physical and chemical degradation of ITNs that reduce their efficacy, inconsistent and improper use by humans, etc. We present a model to investigate the effects of ITN use and mosquito-resistance and adaptation to pyrethroids used to treat bed nets on malaria prevalence and control in malaria endemic regions. The model captures the development and loss of resistance to insecticides, the effects of ITN use on malaria control in a setting where proper and consistent use is not guaranteed, as well as differentiated biting of human hosts by resistant and sensitive mosquitoes. Important thresholds, including the basic reproduction number [Formula: see text], and two parameter groupings that are important for disease control and for establishing the existence of endemic equilibria to the model are calculated. Furthermore, a global sensitivity analysis is carried out to identify important parameters such as insecticide treated bed-net coverage, ITN, the maximum biting rate of resistant mosquitoes, etc., that drive the system and that can be targeted for disease control. Threshold levels of ITN coverage and ITN efficacy required for containing the disease are identified and shown to depend on the type of insecticide-resistance. For example, when mosquito-resistance to insecticides is not permanent and is acquired only through recruitment and the efficacy of ITNs is [Formula: see text], about [Formula: see text] net coverage is required to contain malaria. However, for the same ITN efficacy, i.e., [Formula: see text], approximately [Formula: see text] net coverage is required to contain the disease when resistance to insecticides is permanent and is acquired through recruitment and mutation in mosquitoes. The model exhibits a backward bifurcation, which implies that simply reducing [Formula: see text] slightly below unity might not be enough to contain the disease. We conclude that appropriate measures to reduce or eliminate mosquito-resistance to insecticides, ensure that more people in endemic areas own and use ITNs properly, and that the efficacy of these nets remain high most of the time, as well as educating populations in malaria endemic areas on how to keep mosquito densities low and minimize mosquito bites are important for containing malaria.

Spatial and epidemiological drivers of Plasmodium falciparum malaria among adults in the Democratic Republic of the Congo

BackgroundAdults are frequently infected with malaria and may serve as a reservoir for further transmission, yet we know relatively little about risk factors for adult infections. In this study, we...

Long-lasting insecticidal nets and the quest for malaria eradication: a mathematical modeling approach.

Recent dramatic declines in global malaria burden and mortality can be largely attributed to the large-scale deployment of insecticidal-based measures, namely long-lasting insecticidal nets (LLINs) and indoor residual spraying. However, the sustainability of these gains, and the feasibility of global malaria eradication by 2040, may be affected by increasing insecticide resistance among the Anopheles malaria vector. We employ a new differential-equations based mathematical model, which incorporates the full, weather-dependent mosquito lifecycle, to assess the population-level impact of the large-scale use of LLINs, under different levels of Anopheles pyrethroid insecticide resistance, on malaria transmission dynamics and control in a community. Moreover, we describe the bednet-mosquito interaction using parameters that can be estimated from the large experimental hut trial literature under varying levels of effective pyrethroid resistance. An expression for the basic reproduction number, [Formula: see text], as a function of population-level bednet coverage, is derived. It is shown, owing to the phenomenon of backward bifurcation, that [Formula: see text] must be pushed appreciably below 1 to eliminate malaria in endemic areas, potentially complicating eradication efforts. Numerical simulations of the model suggest that, when the baseline [Formula: see text] is high (corresponding roughly to holoendemic malaria), very high bednet coverage with highly effective nets is necessary to approach conditions for malaria elimination. Further, while >50% bednet coverage is likely sufficient to strongly control or eliminate malaria from areas with a mesoendemic malaria baseline, pyrethroid resistance could undermine control and elimination efforts even in this setting. Our simulations show that pyrethroid resistance in mosquitoes appreciably reduces bednet effectiveness across parameter space. This modeling study also suggests that increasing pre-bloodmeal deterrence of mosquitoes (deterring them from entry into protected homes) actually hampers elimination efforts, as it may focus mosquito biting onto a smaller unprotected host subpopulation. Finally, we observe that temperature affects malaria potential independently of bednet coverage and pyrethroid-resistance levels, with both climate change and pyrethroid resistance posing future threats to malaria control.

Modeling pyrethroids repellency and its role on the bifurcation analysis for a bed net malaria model

• Bed net lethal and repellent effects are incorporated in a dynamical malaria model and the disease contact rates are explicitly modeled by highly nonlinear functions of their rates. • The complete asymptotic behavior of the model is established, using Lyapunov-LaSalle techniques and geometric approach. • An in-depth bifurcation analysis is performed, with all the equilibrium points topologically classified and the existence of trans-critical forward and backward bifurcations established. • Bed net repellency and disease-induced mortality are solely or jointly the causes of backward bifurcation, which impedes the classical requirement that, bringing the basic reproduction number below unity is sufficient to control malaria. • Bed nets with high lethal effect is better that bed nets with high repellency effect.Both bed net repellency and lethal effects decrease disease contact rates, and lethal effect rate does it faster than repellency effect. • Bed net repellency effect regulates the disease burden and its negligence underestimates that burden. We develop and analyze a simple mathematical model for malaria transmission where pyrethroids treated nets (PTNs) are used for control purposes, and in which knock-down/lethal, excito-repellent/deterrent effects are incorporated. We explicitly describe the contact rates between mosquitoes and humans by nonlinear functions of bed net usage and repellency rates. Using center manifold theory, we show that our model exhibits, saddle-node, transcritical forward and backward bifurcation when the reproduction number R 0 crosses one. Our model reveals that repellency effect plays an important role for the existence of both the endemic equilibrium points and the occurrence of backward bifurcation and a threshold repellency rate is calculated. The epidemiological implication of the backward bifurcation is that, reducing R 0 below one alone is not enough to eliminate malaria. We establish that, increasing either the rate of bed nets usage (i.e community protection) or their repellent effect (i.e personal protection) or the combination of both, decreases the contact rates between humans and mosquitoes. As a result, the disease burden metric R 0 is reduced. The global asymptotic stability of equilibrium points are proven using the geometric approach and Lyapunov-LaSalle techniques. Furthermore, we show that neglecting repellency underestimates the basic reproduction number and hinders the control of malaria. The disease free equilibrium is shown to be a saddle-node of co-dimension 1 when R 0 = 1 . We also observe that R 0 is mostly influenced by the bed net coverage rate, repellent effect of pyrethroids and the probability that mosquitoes target human hosts. Our results confirm that PTNs usage is an efficient control strategy to mitigate the malaria ability to spread, and suggest that the utilization of PTNs with high lethal rate, but low repellency rate is better than the use of those with high repellency and low lethal rates.

Sustaining LLIN coverage with continuous distribution: the school net programme in Tanzania

Most malaria-endemic countries have struggled in the past decade to establish effective national-scale continuous distribution mechanisms for long-lasting insecticidal nets (LLINs). Since the implementation of the Tanzania National Voucher Scheme in 2004 and mass-distribution campaigns in 2009–2011 and 2015–2016, Tanzania has been committed to finding new and innovative ways of achieving and maintaining universal bed net coverage. Planning for the School Net Programme (SNP) began in 2011 and in 2013, the country piloted a SNP in three regions. Nets were distributed annually to children attending schools in selected primary and secondary grades. Intra-family re-distribution was assumed, and hence the family as a whole, rather than just the children themselves, were the targeted beneficiaries. The programme has since expanded to 14 regions and has seen six rounds of annual distribution. In its fifth year, 3 million nets were distributed at a cost of USD 3.64 per net and USD 0.60 per person-year of protection (including the net). ITN access and use were maintained at a high level (~ 50–75%) over the first 4 years of distribution within selected evaluation areas, even in the absence of a mass distribution event. Net distribution through primary schools has proven to be a feasible and effective strategy for maintaining consistently high coverage in Tanzania.

Indoor use of attractive toxic sugar bait in combination with long-lasting insecticidal net against pyrethroid-resistant Anopheles gambiae: an experimental hut trial in Mb\xe9, central C\xf4te d\u2019Ivoire

BackgroundIndoor attractive toxic sugar bait (ATSB) has potential as a supplementary vector-control and resistance-management tool, offering an alternative mode of insecticide delivery to current core vector-control interventions, with potential to deliver novel insecticides. Given the high long-lasting insecticidal bed net (LLIN) coverage across Africa, it is crucial that the efficacy of indoor ATSB in combination with LLINs is established before it is considered for wider use in public health.MethodsAn experimental hut trial to evaluate the efficacy of indoor ATSB traps treated with 4% boric acid (BA ATSB) or 1% chlorfenapyr (CFP ATSB) in combination with untreated nets or LLINs (holed or intact), took place at the M’bé field station in central Côte d’Ivoire against pyrethroid resistant Anopheles gambiae sensu lato.ResultsThe addition of ATSB to LLINs increased the mortality rates of wild pyrethroid-resistant An. gambiae from 19% with LLIN alone to 28% with added BA ATSB and to 39% with added CFP ATSB (p < 0.001). Anopheles gambiae mortality with combined ATSB and untreated net was similar to that of combined ATSB and LLIN regardless of which insecticide was used in the ATSB. The presence of holes in the LLIN did not significantly affect ATSB-induced An. gambiae mortality. Comparative tests against pyrethroid resistant and susceptible strains using oral application of ATSB treated with pyrethroid demonstrated 66% higher survival rate among pyrethroid-resistant mosquitoes.ConclusionIndoor ATSB traps in combination with LLINs enhanced the control of pyrethroid-resistant An. gambiae. However, many host-seeking An. gambiae entering experimental huts with indoor ATSB exited into the verandah trap without sugar feeding when restricted from a host by a LLIN. Although ATSB has potential for making effective use of classes of insecticide otherwise unsuited to vector control, it does not exempt potential selection of resistance via this route.

Predictors of Malaria Prevalence and Coverage of Insecticide-Treated Bednets among Under-Five Children in the Buea Health District, South West Region, Cameroon

Introduction: Cameroon is a hyperendemic country to malaria where it remains a major public health concern, especially amongst children under-five. Insecticide-treated bednets (ITBNs) is the main control strategies. This study aimed at determining the predictors of malaria prevalence and coverage of ITBNs among under-five children in the Buea Health District (BHD), South West Region of Cameroon in other to reduce the morbidity and mortality of malaria. Methods: A cross-sectional study was carried out in the BHD which is a malaria-hyperendemic area. Every head (female/male) of the household who was present at home at the time of data collection was randomly interviewed using a structured questionnaire. Under-five children were ascertained for malaria using microscopy, with a temperature of ≥37.50°C. Results: Out of 391 children (mean age = 19.7 month, SD = 2.5) who were selected and ascertained for malaria, the overall malaria prevalence was 13.04% (95% CI: 10.04 - 16.78). In a multivariate analysis after adjusting for confounders, female parents/guardians (AOR = 0.53, 95% CI: 0.29 - 0.91) was associated with low risk of malaria while parents/guardians with no formal/primary educational (AOR = 3.3, 95% CI: 1.76 - 4.04) and children who did not use ITBN (AOR = 1.40, 95% CI: 1.08 - 2.51) were associated with an increased risk of malaria. Out of the selected children, 84.4% possessed ITBN (95% CI: 80.4 - 87.7) while 72.6% (95% CI: 67.9 - 76.8) used ITBN. In a multivariate after adjusting for confounders, Bova health area showed a significantly lower usage of ITBNs (χ 2 = 14.053, p = 0.003). Conclusion: The findings indicate that increased ITBN usage, increased parents/guardians’ educational level and good knowledge of ITBN is required to lower the risk of under-five children being infected with malaria. Health area of residence greatly influences the direct relationship between bednets possession and usage. These, therefore, indicates the possession of ITBN doesn’t mean their usage. The Cameroon National malaria control programs should consider the realities of the living conditions of the population for the implementation of better policies.

Knowledge of Health Communications Management and Treatment Seeking-Behavior Regarding Malaria in Uganda

In Uganda, there is still insufficient comprehension of malaria as a lethal disease especially in rural areas despite universal bed-net distribution coverage and effective anti-malarial treatment. Aim: To get evidence-based knowledge to establish the contribution of an individuals’ knowledge from various health communications that could increase their active involvement in health care especially seeking timely appropriate treatment for malaria or suspected malaria. Method: A cross-sectional survey using a correlational design was employed on a clustered sample of 380 rural households in 05 sub-counties of Kanungu district. Data were corrected between October 2016-January 2017 using researcher-administered questionnaires, key-informant interviews and focus group discussions. Correlation analysis was done. Result: There is a significant positive relationship between knowledge of health communications and treatment-seeking behavior (r = 0.312; p ≤ 0.01). Conclusion: Exposure to consistent Behavioral Change Communications messages influences treatment-seeking behaviour. Thus, in malaria-prone communities, it appears that other factors including sufficient targeted persuasive health communication are lacking in influencing personal orientations towards treatment-seeking behaviour. Therefore, proper Health Communications management supplements efforts from other disciplines and players, against malaria in Uganda.

Mortality and health survey, Walikale, Democratic Republic of the Congo, 2017: an example of the use of survey data for humanitarian program planning

BackgroundDuring humanitarian crises, health information systems are often lacking and surveys are a valuable tool to assess the health needs of affected populations. In 2013, a mortality and health survey undertaken by Médecins Sans Frontières (MSF) in the conflict affected Walikale territory of North Kivu, Democratic Republic of the Congo (DRC), indicated mortality rates exceeding humanitarian crisis thresholds and a high burden of mortality and morbidity due to malaria. In late 2017, after a period of relative stability, MSF reassessed the health status of the population through a second survey to guide ongoing operations.MethodsA two-stage cluster survey, selecting villages using probability proportional to size and households using random walk procedures, was conducted. Household members were interviewed on morbidity and mortality, healthcare use, vaccination status, and bednet availability.ResultsThe sample included 5711 persons in 794 households. The crude mortality rate (CMR) and under-five mortality rate (U5MR) were 0.98 per 10,000 persons/day (95% confidence interval (CI) 0.78–1.2) and 1.3 per 10,000 persons/day (95% CI): 0.82–2.0), respectively. The most frequently reported causes of death were fever/malaria (31%), diarrhoea (15%) and respiratory infections (8%). In 89% of households at least one person was reported as falling ill in the previous 2 weeks, and 58% sought healthcare. Cost was the main barrier amongst 58% of those who did not seek healthcare. Coverage of measles-containing-vaccine was 62% in under-fives. Sufficient bednet coverage (1 bednet/2 people) was reported from 17% of households.ConclusionThe second survey illustrates that although mortality is now just below crisis thresholds, the area still experiences excess mortality and has substantial health needs. The study results have supported the further expansion of integrated community case management to improve access to care for malaria, diarrhoea and respiratory infections. Such surveys are important to orient operations to the health needs of the population being served and also highlight the ongoing vulnerability of populations after humanitarian crises.

Higher risk of malaria transmission outdoors than indoors by Nyssorhynchus darlingi in riverine communities in the Peruvian Amazon

BackgroundMalaria remains an important public health problem in Peru where incidence has been increasing since 2011. Of over 55,000 cases reported in 2017, Plasmodium vivax was the predominant species (76%), with P. falciparum responsible for the remaining 24%. Nyssorhynchus darlingi (previously Anopheles darlingi) is the main vector in Amazonian Peru, where hyperendemic Plasmodium transmission pockets have been found. Mazán district has pronounced spatial heterogeneity of P. vivax malaria. However, little is known about behavior, ecology or seasonal dynamics of Ny. darlingi in Mazán. This study aimed to gather baseline information about bionomics of malaria vectors and transmission risk factors in a hyperendemic malaria area of Amazonian Peru.MethodsTo assess vector biology metrics, five surveys (two in the dry and three in the rainy season), including collection of sociodemographic information, were conducted in four communities in 2016–2017 on the Napo (Urco Miraño, URC; Salvador, SAL) and Mazán Rivers (Visto Bueno, VIB; Libertad, LIB). Human-biting rate (HBR), entomological inoculation rate (EIR) and human blood index (HBI) were measured to test the hypothesis of differences in entomological indices of Ny. darlingi between watersheds. A generalized linear mixed effect model (GLMM) was constructed to model the relationship between household risk factors and the EIR.ResultsNyssorhynchus darlingi comprised 95% of 7117 Anophelinae collected and its abundance was significantly higher along the Mazán River. The highest EIRs (3.03–4.54) were detected in March and June in URC, LIB and VIB, and significantly more Ny. darlingi were infected outdoors than indoors. Multivariate analysis indicated that the EIR was >12 times higher in URC compared with SAL. The HBI ranged from 0.42–0.75; humans were the most common blood source, followed by Galliformes and cows. There were dramatic differences in peak biting time and malaria incidence with similar bednet coverage in the villages.ConclusionsNyssorhynchus darlingi is the predominant contributor to malaria transmission in the Mazán District, Peru. Malaria risk in these villages is higher in the peridomestic area, with pronounced heterogeneities between and within villages on the Mazán and the Napo Rivers. Spatiotemporal identification and quantification of the prevailing malaria transmission would provide new evidence to orient specific control measures for vulnerable or at high risk populations.

Bio-efficacy and physical integrity of piperonylbutoxide coated combination net (PermaNet\xae 3.0) against pyrethroid resistant population of Anopheles gambiae s.l. and Culex quinquefasciatus mosquitoes in Ethiopia

BackgroundPermaNet® 3.0 is a deltamethrin-treated combination long-lasting insecticidal net with the addition of synergist piperonylbutoxide (PBO) on its roof section. It is designed to overcome the challenge posed by pyrethroid resistant vector populations against mainstream long-lasting insecticidal nets impregnated with pyrethroids only. The objective of this study was to determine insecticide resistance status of Anopheline and Culicine mosquitoes, to evaluate the bio-efficacy of PermaNet® 3.0 nets and to assess household factors affecting the physical integrity of PermaNet® 3.0 after 3 years of use.MethodsInsecticide susceptibility test was conducted using the WHO tube test. Bio-activity of PermaNet® 3.0 samples was evaluated using the WHO cone bioassay. Cross-sectional survey was conducted on 150 randomly selected households from two districts to determine household factors affecting net utilization. One hundred fifty PermaNet® 3.0 nets were randomly collected from the community with replacement after 3 years of deployment and physical integrity of each net was assessed.ResultsBoth Anopheles gambiae sensu lato and Culex quinquefasciatus developed resistance against permethrin and deltamethrin. However, following pre-exposure to synergist PBO the susceptibility of mosquito population increased to both permethrin (from 39% without to 92% with PBO against An. gambiae and from 28% without to 94% with PBO against Culex quinquefasciatus) and deltamethrin (from 52% without to 99% with PBO against An. gambiae and from 43% without to 98% with PBO against Culex quinquefasciatus). Eighty percent (80%) mortality was recorded in wild population of An. gambiae s.l. exposed to unused PermaNet® 3.0, but its bioactivity subsequently declined as washing frequency increased from 0 to 20. The PBO coated roof section of unused PermaNet® 3.0 resulted in higher mosquito mortality (100%) compared to the side panels without PBO (85%). House structure, cooking and washing habits, and damage due to household pests were cited as determinants associated with bed net deterioration. Bed net proportionate hole index (pHI) was ranged from 0 to 6064. Of the 150 PermaNet® 3.0 nets assessed 80, 29 and 41 were considered as ‘good’, ‘acceptable’ and ‘too torn’, respectively.ConclusionsThe bio-efficacy evaluation of PermaNet® 3.0 from Jimma area, southwestern Ethiopia showed moderate efficacy against pyrethroid resistant population of An. gambiae and Culex quinquefasciatus. Thus, NMCPs in parallel to deployment of LLINs, should implement timely insecticide resistance management and integrated vector management strategies to slowdown the evolution and further spread of insecticide resistance. Household factors such as, housing conditions, open flame fire used for cooking and rodent attack were identified as factors contributing to the observed reduced bed net physical integrity in the study area. Universal coverage of bed nets should be accompanied with community awareness creation and training on net utilization and handling.

A Mathematical Model for the Population Dynamics of Malaria with a Temperature Dependent Control

In this work, we develop a mathematical model for malaria transmission that investigates the impact of temperature on the efficacy of ITNs. The disease free state of the autonomous version of the formulated model is seen to be globally asymptotically stable in the absence of disease induced mortality when the associated reproduction number is less than unity. Also, when the associated reproduction number of the non-autonomous model is greater than unity, the disease persist in the population. Sensitivity and uncertainty analysis of the autonomous model, using the associated reproduction number, number of infected humans and vectors as response functions, show that the probability of transmission from human to vectors ( $$\beta _{hv}$$ ), maximum biting rate of vectors ( $$b_{max}$$ ), vector carrying capacity ( $$k_v$$ ) as well as ITN efficacy and coverage ( $$\varepsilon _b$$ and $$b_o$$ ) have the most impact on all three response functions. In the non-autonomous model, for temperature values in the range $$[18\pm 4-32\pm 4]\,^\circ $$ C and using the number of infected humans and vectors as response functions, it can be seen that the bed-net coverage lost its significance for temperature values in the range $$[22\pm 4-30\pm 4]\,^\circ $$ C and $$[22\pm 4-26\pm 4] \,^\circ $$ C respectively. Numerical simulations of the time-averaged reproduction number for the case where the efficacy of the bed-net is temperature-dependent showed that temperature values in the range [22–27] $$\,^\circ $$ C effects the efficacy of the bed-nets most. Numerical simulations of the non-autonomous model for the case where ITN efficacy is temperature-dependent, we determine temperature ranges that make for increase in the effectiveness of the bed-nets in the fight against malaria.

Malaria Control and Infant Mortality in Africa

Has massive distribution of insecticide-treated-nets contributed to the reduction in infant mortality in Sub-Saharan Africa over the past 15 years? Using large household surveys collected in 16 countries and exploiting the spatial correlation in distribution campaigns, we estimate the relationship between the diffusion of bednets and the progress in child survival. We find no evidence of a causal link in cities, and no impact either in rural areas with low malaria prevalence. By contrast, in highly malarious rural areas where bednet coverage reached high levels, above 75% of households, infant mortality has been reduced by at least 3 percentage points, which amounts to 25% of the initial mortality. The identified impact is even higher for the children of mothers with no education. It lies at the upper bound found with RCTs, most likely because those were implemented in contexts with lower mortality and/or malaria prevalence.

Mathematical modelling of the impact of expanding levels of malaria control interventions on Plasmodium vivax

Plasmodium vivax poses unique challenges for malaria control and elimination, notably the potential for relapses to maintain transmission in the face of drug-based treatment and vector control strategies. We developed an individual-based mathematical model of P. vivax transmission calibrated to epidemiological data from Papua New Guinea (PNG). In many settings in PNG, increasing bed net coverage is predicted to reduce transmission to less than 0.1% prevalence by light microscopy, however there is substantial risk of rebounds in transmission if interventions are removed prematurely. In several high transmission settings, model simulations predict that combinations of existing interventions are not sufficient to interrupt P. vivax transmission. This analysis highlights the potential options for the future of P. vivax control: maintaining existing public health gains by keeping transmission suppressed through indefinite distribution of interventions; or continued development of strategies based on existing and new interventions to push for further reduction and towards elimination.

Household ownership and utilization of insecticide-treated nets under the Regional Artemisinin Resistance Initiative in Myanmar

BackgroundMalaria is a major public health problem in Myanmar with reported artemisinin resistance. Myanmar promotes the use of insecticide-treated nets (ITNs) through the free delivery of long-lasting insecticide nets (LLINs) with target coverage of at least 80% in moderate and high-risk areas by 2014. Migrant people are at greater risk of malaria. They have significant barriers to health care services for febrile illness and malaria. Thus, a community-based survey was conducted among the migrant population to assess the ownership and utilization of bed nets (ITN/LLINs) for malaria.MethodsThe study analyzed secondary data from a community-based malaria survey conducted in 2014 among migrant population in 30 randomly selected townships out of 52 Regional Artemisinin Resistance Initiative (RAI) townships. In each township, five migrant sites were randomly selected (total of 150 migrant sites). A total of 3933 households (approximately 125 households from each township) were selected.ResultsOf 3923 households assessed, 97% had access to at least one bed net (any type), but only half had access to ITN/LLINs. Only 24% of households had adequate ITN/LLIN access (at least one ITN/LLIN per two persons). In terms of household utilization, 94.3% slept under a bed net (any type) the previous night. Only 43.4% slept under an ITN/LLIN. ITN/LLIN utilization in children under 5 years and pregnant women (high-malaria risk groups) was 45.3 and 46.6%, respectively. Of all nets, 31.3% had holes or had already undergone repairs. In terms of insecticide treatment status, 52.9% of bed nets were untreated and 35.9% of ITNs had not been treated with insecticide for more than a year.ConclusionThis study highlights poor access and high utilization of ITN/LLINs among migrant population, particularly among children and pregnant women. It highlights the need for improving bed net coverage and access to ITN/LLINs through bed net distributions and/or social marketing with the focus on migrant population and targeting of households with children and pregnant women.

Trends of Plasmodium falciparum prevalence in two communities of Muheza district North-eastern Tanzania: correlation between parasite prevalence, malaria interventions and rainfall in the context of re-emergence of malaria after two decades of progressively declining transmission

BackgroundAlthough the recent decline of malaria burden in some African countries has been attributed to a scale-up of interventions, such as bed nets (insecticide-treated bed nets, ITNs/long-lasting insecticidal nets, LLINs), the contribution of other factors to these changes has not been rigorously assessed. This study assessed the trends of Plasmodium falciparum prevalence in Magoda (1992–2017) and Mpapayu (1998–2017) villages of Muheza district, North-eastern Tanzania, in relation to changes in the levels of different interventions and rainfall patterns.MethodsIndividuals aged 0–19 years were recruited in cross-sectional surveys to determine the prevalence of P. falciparum infections in relation to different malaria interventions deployed, particularly bed nets and anti-malarial drugs. Trends and patterns of rainfall in Muheza for 35 years (from 1981 to 2016) were assessed to determine changes in the amount and pattern of rainfall and their possible impacts on P. falciparum prevalence besides of those ascribed to interventions.ResultsHigh prevalence (84–54%) was reported between 1992 and 2000 in Magoda, and 1998 and 2000 in Mpapayu, but it declined sharply from 2001 to 2004 (from 52.0 to 25.0%), followed by a progressive decline between 2008 and 2012 (to ≤ 7% in both villages). However, the prevalence increased significantly from 2013 to 2016 reaching ≥ 20.0% in 2016 (both villages), but declined in the two villages to ≤ 13% in 2017. Overall and age specific P. falciparum prevalence decreased in both villages over the years but with a peak prevalence shifting from children aged 5–9 years to those aged 10–19 years from 2008 onwards. Bed net coverage increased from < 4% in 1998 to > 98% in 2001 and was ≥ 85.0% in 2004 in both villages; followed by fluctuations with coverage ranging from 35.0 to ≤ 98% between 2008 and 2017. The 12-month weighted anomaly standardized precipitation index showed a marked rainfall deficit in 1990–1996 and 1999–2010 coinciding with declining prevalence and despite relatively high bed net coverage from 2000. From 1992, the risk of infection decreased steadily up to 2013 when the lowest risk was observed (RR = 0.07; 95% CI 0.06–0.08, P < 0.001), but it was significantly higher during periods with positive rainfall anomalies (RR = 2.79; 95% CI 2.23–3.50, P < 0.001). The risk was lower among individuals not owning bed nets compared to those with nets (RR = 1.35; 95% CI 1.22–1.49, P < 0.001).ConclusionsA decline in prevalence up to 2012 and resurgence thereafter was likely associated with changes in monthly rainfall, offset against changing malaria interventions. A sustained surveillance covering multiple factors needs to be undertaken and climate must be taken into consideration when relating control interventions to malaria prevalence.

Modelling the effect of bednet coverage on malaria transmission in South Sudan.

A campaign for malaria control, using Long Lasting Insecticide Nets (LLINs) was launched in South Sudan in 2009. The success of such a campaign often depends upon adequate available resources and reliable surveillance data which help officials understand existing infections. An optimal allocation of resources for malaria control at a sub-national scale is therefore paramount to the success of efforts to reduce malaria prevalence. In this paper, we extend an existing SIR mathematical model to capture the effect of LLINs on malaria transmission. Available data on malaria is utilized to determine realistic parameter values of this model using a Bayesian approach via Markov Chain Monte Carlo (MCMC) methods. Then, we explore the parasite prevalence on a continued rollout of LLINs in three different settings in order to create a sub-national projection of malaria. Further, we calculate the model’s basic reproductive number and study its sensitivity to LLINs’ coverage and its efficacy. From the numerical simulation results, we notice a basic reproduction number, , confirming a substantial increase of incidence cases if no form of intervention takes place in the community. This work indicates that an effective use of LLINs may reduce and hence malaria transmission. We hope that this study will provide a basis for recommending a scaling-up of the entry point of LLINs’ distribution that targets households in areas at risk of malaria.