115 research outputs found
Mathematical Evaluation of Community Level Impact of Combining Bed Nets and Indoor Residual Spraying upon Malaria Transmission in Areas where the main Vectors are Anopheles Arabiensis Mosquitoes.
No full textIndoor residual insecticide spraying (IRS) and long-lasting insecticide treated nets (LLINs) are commonly used together even though evidence that such combinations confer greater protection against malaria than either method alone is inconsistent. A deterministic model of mosquito life cycle processes was adapted to allow parameterization with results from experimental hut trials of various combinations of untreated nets or LLINs (Olyset, PermaNet 2.0, Icon Life nets) with IRS (pirimiphos methyl, lambda cyhalothrin, DDT), in a setting where vector populations are dominated by Anopheles arabiensis, so that community level impact upon malaria transmission at high coverage could be predicted. Intact untreated nets alone provide equivalent personal protection to all three LLINs. Relative to IRS plus untreated nets, community level protection is slightly higher when Olyset or PermaNet 2.0 nets are added onto IRS with pirimiphos methyl or lambda cyhalothrin but not DDT, and when Icon Life nets supplement any of the IRS insecticides. Adding IRS onto any net modestly enhances communal protection when pirimiphos methyl is sprayed, while spraying lambda cyhalothrin enhances protection for untreated nets but not LLINs. Addition of DDT reduces communal protection when added to LLINs. Where transmission is mediated primarily by An. arabiensis, adding IRS to high LLIN coverage provides only modest incremental benefit (e.g. when an organophosphate like pirimiphos methyl is used), but can be redundant (e.g. when a pyrethroid like lambda cyhalothin is used) or even regressive (e.g. when DDT is used for the IRS). Relative to IRS plus untreated nets, supplementing IRS with LLINs will only modestly improve community protection. Beyond the physical protection that intact nets provide, additional protection against transmission by An. arabiensis conferred by insecticides will be remarkably small, regardless of whether they are delivered as LLINs or IRS. The insecticidal action of LLINs and IRS probably already approaches their absolute limit of potential impact upon this persistent vector so personal protection of nets should be enhanced by improving the physical integrity and durability. Combining LLINs and non-pyrethroid IRS in residual transmission systems may nevertheless be justified as a means to manage insecticide resistance and prevent potential rebound of not only An. arabiensis, but also more potent, vulnerable and historically important species such as Anopheles gambiae and Anopheles funestus
Machine Learning and Data Mining-Based Methods to Estimate Parity Status and Age of Wild Mosquito Vectors of Infectious Diseases from Near-Infrared Spectra
No full textPrevious studies show that a trained partial least square regresser [sic] (PLSR) from near-infrared spectra classify laboratory and semi-field raised mosquitoes into less than or ≥ to seven days old with an average accuracy of 80%. This dissertation demonstrates that training models on near-infrared spectra (NIRS) using artificial neural network (ANN) as an architecture yields models with higher accuracies than training models using partial least squares (PLS) as an architecture. In addition, irrespective of the model architecture used, direct training of a binary classifier scores higher accuracy than training a regresser and interpreting it as a binary classifier. Furthermore, for the first time, this dissertation shows that training ANN models on autoencoded near-infrared spectra yields models that estimate parity status of wild mosquitoes with an accuracy of ≈93%, which is strong enough to support NIRS models as an alternative to ovary dissections. Results from this dissertation also show that there is no significant difference between spectra collected from semi-field raised and wild mosquitoes of the same species, supporting the on-going practice of training models on semi-field raised mosquitoes to estimate the age class in days of wild mosquitoes. Finally, the study shows that an ANN model trained on semi-field mosquitoes classifies wild mosquitoes into either less than or ≥ to seven days old with an average accuracy of 76%. In conclusion, the results in this dissertation strongly suggest the use of ANNs as a suitable architecture to train models that estimate parity status and age in days of wild mosquito vectors of infectious diseases. The results further suggest near-infrared spectroscopy as an appropriate alternative tool to estimate different parameters of mosquito vectors of infectious diseases
Near Infrared Spectroscopy for Estimating the Age of Malaria Transmitting Mosquitoes
No full textWe explore the use of near infrared spectrometry to classifying the age of a wild malaria transmitting mosquito. In Chapter Two, using a different set of lab-reared mosquitoes, we replicate the Mayagaya et al. study of the accuracy of near-infrared spectrometry (NIRS) to estimate the age of lab-reared mosquitoes, reproducing the published accuracy. Our results strengthen the Mayagaya et. al study and increase confidence in using NIRS to estimate age classes of mosquitoes. In the field, we wish to classify the ages of wild, not lab-reared mosquitoes, but the necessary training data from wild mosquitoes is difficult to find. Applying a model trained on spectra from lab-reared mosquitoes to estimate the age of wild mosquitoes is appropriate only if spectra collected from lab-reared mosquitoes are equivalent to those collected from wild mosquitoes. In Chapter Three, we apply k means cluster analysis to a mixture of spectra collected from lab-reared and wild Anopheles arabiensis mosquitoes to determine if there is significant difference between these spectra. We find no significant difference (P = 0.245) in distributions between the wild and lab-reared mosquitoes in the two formed clusters. The two formed clusters have average silhouette coefficient values (cluster quality measure) of 0.51 and 0.77, respectively, which shows that the clusters were reasonable and strong, respectively. Basing on results from Chapter Three, we estimate the age class of wild Anopheles arabiensis mosquitoes using a classification model trained on lab-reared Anopheles arabiensis. We validate the accuracy of the model by comparing its estimates with ovary dissection estimates. While our model estimated 86% and 14% of wild Anopheles arabiensis to be \u3c 7 and 7 days old, respectively, ovary dissection estimated 72% as young and 28% as old. Studies show that wild mosquito populations generally consist of more young than old mosquitoes. Therefore, our model estimates age of wild mosquitoes in consistency with ovary dissection and other studies conducted to determine age structure of wild mosquitoes
Bioinformatics Systems And Mathematical Models For Improved Understanding Of Malaria Transmission, Control, And Elimination
No full textThe leading malaria vector control strategies (i.e., long-lasting insecticidal nets and indoor residual spraying) can reduce indoor transmission, but these tools alone are insufficient to eliminate it. Strategies that target adult mosquitoes when they feed on humans or animals outdoors or target mosquito immature stages are also needed to achieve malaria elimination. Improved data systems for integrating
diverse experimental observations and research groups, as well as process-explicit mathematical models for evaluating them are both essential to achieving these goals.
We have developed a generic schema and data repositories for the studies of malaria vectors that encompass a wide variety of different experimental designs that rapidly generate large data volumes. We extended a malaria transmission model to examine the relationship between transmission, control, and the proportion of blood
meals a vector population obtains from humans: Assuming the lower limit for this indicator of human feeding preference enabled derivation of simplified models for zoophagic vectors. We present differential equation models to describe the biological processes that mediate novel strategies to control malaria vectors by autodissemination
of pyripoxyfen (PPF) as it is transferred from treated stations to the gravid
mosquitoes and then to the aquatic habitats where it inhibits mosquito emergence.
Data from most of the mosquito studies we reviewed conformed to our
generic schema with four tables recording the experimental design, sorting of collections, details of samples, and additional observations. Our corresponding online repository includes 20 experiments, 8 projects, and 15 users at two institutes, resulting in 10 peer-reviewed publications. For zoophagic vectors, the results from
model can be used to forecast the likely immediate and delayed impacts of an intervention using only three field-measurable parameters. For the autodissemination of PPF, sensitivity analysis indicates success of the strategy is plausible because the ≥ 80% coverage of aquatic habitats with PPF appears achievable with modest, biologically plausible values of field-measurable input parameters.
Therefore, we have applied two of the computational sciences aspects (i.e., research data preparation using computer systems and scenario analysis with mathematical models) to address obstacles to the control and elimination of malaria
Detection of Outliers in Time Series Data
No full textThis thesis presents the detection of time series outliers. The data set used in this work is provided by the GasDay Project at Marquette University, which produces mathematical models to predict the consumption of natural gas for Local Distribution Companies (LDCs). Flow with no outliers is required to develop and train accurate models. GasDay is using statistical approaches motivated by normally distributed samples such as the 3 -sigma rule and the 5 -sigma rule to aid the experts in detecting outliers in residuals from the models. However, the Jarque-Bera statistical test shows that the residuals from the GasDay models are not normally distributed.
We present an explanation of Density Based Spatial Clustering of Applications with Noise (DBSCAN) and how it is used to detect time series outliers. We have introduced a new application for the DBSCAN algorithm by adapting it to detect outliers in natural gas flow. The performance of DBSCAN is compared with GasDay\u27s existing technique. Five data sets from temperature-sensitive operating areas with identified outliers and 1000 data sets with synthetic outliers are used in the evaluation process. The 1000 synthetic data sets are prepared using the same empirical distribution as one of the identified data set. This work indicates that DBSCAN has shown some improvement in detecting outliers over GasDays existing technique and merits further exploration
Biologically meaningful coverage indicators for eliminating malaria transmission.
No full textMosquitoes, which evade contact with long-lasting insecticidal nets and indoor residual sprays, by feeding outdoors or upon animals, are primary malaria vectors in many tropical countries. They can also dominate residual transmission where high coverage of these front-line vector control measures is achieved. Complementary strategies, which extend insecticide coverage beyond houses and humans, are required to eliminate malaria transmission in most settings. The overwhelming diversity of the world's malaria transmission systems and optimal strategies for controlling them can be simply conceptualized and mapped across two-dimensional scenario space defined by the proportion of blood meals that vectors obtain from humans and the proportion of human exposure to them which occurs indoors
Effective Autodissemination of Pyriproxyfen to Breeding Sites by the Exophilic Malaria Vector Anopheles Arabiensis in Semi-Field Settings in Tanzania.
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Malaria vector control strategies that target adult female mosquitoes are challenged by the emergence of insecticide resistance and behavioural resilience. Conventional larviciding is restricted by high operational costs and inadequate knowledge of mosquito-breeding habitats in rural settings that might be overcome by the juvenile hormone analogue, Pyriproxyfen (PPF). This study assessed the potential for Anopheles arabiensis to pick up and transfer lethal doses of PPF from contamination sites to their breeding habitats (i.e. autodissemination of PPF). A semi-field system (SFS) with four identical separate chambers was used to evaluate PPF-treated clay pots for delivering PPF to resting adult female mosquitoes for subsequent autodissemination to artificial breeding habitats within the chambers. In each chamber, a tethered cow provided blood meals to laboratory-reared, unfed female An. arabiensis released in the SFS. In PPF-treated chambers, clay pot linings were dusted with 0.2 - 0.3 g AI PPF per pot. Pupae were removed from the artificial habitats daily, and emergence rates calculated. Impact of PPF on emergence was determined by comparing treatment with an appropriate control group. Mean (95%CI) adult emergence rates were (0.21 +/- 0.299) and (0.95 +/- 0.39) from PPF-treated and controls respectively (p < 0.0001). Laboratory bioassay of water samples from artificial habitats in these experiments resulted in significantly lower emergence rates in treated chambers (0.16 +/- 0.23) compared to controls 0.97 +/- 0.05) (p < 0.0001). In experiments where no mosquitoes introduced, there were no significant differences between control and treatment, indicating that transfer of PPF to breeding sites only occurred when mosquitoes were present; i.e. that autodissemination had occurred. Treatment of a single clay pot reduced adult emergence in six habitats to (0.34 +/- 0.13) compared to (0.98 +/- 0.02) in the controls (p < 0.0001), showing a high level of habitats coverage amplification of the autodissemination event. The study provides proof of principle for the autodissemination of PPF to breeding habitats by malaria vectors. These findings highlight the potential for this technique for outdoor control of malaria vectors and call for the testing of this technique in field trials.\u
Increasing role of Anopheles funestus and Anopheles arabiensis in malaria transmission in the Kilombero Valley, Tanzania
No full textIn order to sustain the gains achieved by current malaria control strategies, robust surveillance systems that monitor dynamics of vectors and their roles in malaria transmission over time are essential. This longitudinal study demonstrates the trends in malaria vector dynamics and their relative contribution to malaria transmission in hyperendemic transmission settings in Tanzania.; The study was conducted in two villages within the Kilombero Valley, in rural Tanzania for five consecutive years (2008-2012). Seventy-two houses were selected per village and each house was sampled for mosquitoes monthly using a CDC light trap. Collected mosquitoes were assessed for species identity and sporozoite infection status using PCR and ELISA, respectively. Anopheles funestus and Anopheles arabiensis susceptibility to insecticides was assessed using WHO guidelines.; A total of 100,810 malaria vectors were collected, of which 76% were Anopheles gambiae s. l. and 24% were An. funestus. Of all An. funestus samples that amplified with PCR (n = 2,737), 97% were An. funestus s.s., 2% were Anopheles rivorulum and 1% Anopheles leesoni. Whereas for An. gambiae s.l. (n = 8,117), 93% were An. arabiensis and 7% were Anopheles gambiae s.s. The proportion of An. gambiae s.s. identified by PCR (2,924) declined from 0.2% in the year 2008 to undetectable levels in 2012. Malaria transmission intensity significantly decreased from an EIR of 78.14 infectious bites/person/year in 2008 to 35 ib/p/yr in 2011 but rebounded to 226 ib/p/yr in 2012 coinciding with an increased role of An. funestus in malaria transmission. Insecticide susceptibility tests indicated high levels of resistance in An. funestus against deltamethrin (87%), permethrin (65%), lambda cyhalothrin (74%), bendiocarb (65%), and DDT (66%). Similarly, An. arabiensis showed insecticide resistance to deltamethrin (64%), permethrin (77%) and lambda cyhalothrin (42%) in 2014.; The results indicate the continuing role of An. arabiensis and the increasing importance of An. funestus in malaria transmission, and pyrethroid resistance development in both species. Complementary vector control and surveillance tools are needed that target the ecology, behaviour and insecticide resistance management of these vector species, in order to preserve the efficacy of LLINs
Why lockdown? Why national unity? Why global solidarity? Simplified arithmetic tools for decision-makers, health professionals, journalists and the general public to explore containment options for the 2019 novel coronavirus
No full textAs every country in the world struggles with the ongoing COVID-19 pandemic, it is essential that as many people as possible understand the epidemic containment, elimination and exclusion strategies required to tackle it. Simplified arithmetic models of COVID-19 transmission, control and elimination are presented in user-friendly Shiny and Excel formats that allow non-specialists to explore, query, critique and understand the containment decisions facing their country and the world at large. Although the predictive model is broadly applicable, the simulations presented are based on parameter values representative of the United Republic of Tanzania, which is still early enough in its epidemic cycle and response to avert a national catastrophe. The predictions of these models illustrate (1) why ambitious lock-down interventions to crush the curve represent the only realistic way for individual countries to contain their national-level epidemics before they turn into outright catastrophes, (2) why these need to be implemented so early, so stringently and for such extended periods, (3) why high prevalence of other pathogens causing similar symptoms to mild COVID-19 precludes the use of contact tracing as a substitute for lock down interventions to contain and eliminate epidemics, (4) why partial containment strategies intended to merely flatten the curve, by maintaining epidemics at manageably low levels, are grossly unrealistic, and (5) why local elimination may only be sustained after lock down ends if imported cases are comprehensively excluded, so international co-operation to conditionally re-open trade and travel between countries certified as free of COVID-19 represents the best strategy for motivating progress towards pandemic eradication at global level. The three sequential goals that every country needs to emphatically embrace are contain, eliminate and exclude. As recently emphasized by the World Health Organization, success will require widespread genuine national unity and unprecedented global solidarity
A Need for Better Housing to Further reduce Indoor Malaria Transmission in Areas with High Bed Net Coverage.
No full textThe suppression of indoor malaria transmission requires additional interventions that complement the use of insecticide treated nets (ITNs) and indoor residual spraying (IRS). Previous studies have examined the impact of house structure on malaria transmission in areas of low transmission. This study was conducted in a high transmission setting and presents further evidence about the association between specific house characteristics and the abundance of endophilic malaria vectors. Mosquitoes were sampled using CDC light traps from 72 randomly selected houses in two villages on a monthly basis from 2008 to 2011 in rural Southern Tanzania. Generalized linear models using Poisson distributions were used to analyze the association of house characteristics (eave gaps, wall types, roof types, number of windows, rooms and doors, window screens, house size), number of occupants and ITN usage with mean catches of malaria vectors (An.gambiae s.l. and An. funestus). A total of 36490 female An. gambiae s.l. were collected in Namwawala village and 21266 in Idete village. As for An. funestus females, 2268 were collected in Namwawala and 3398 in Idete. Individually, each house factor had a statistically significant impact (p < 0.05) on the mean catches for An. gambiae s.l. but not An. funestus. A multivariate analysis indicated that the combined absence or presence of eaves, treated or untreated bed-nets, the number of house occupants, house size, netting over windows, and roof type were significantly related (p < 0.05) to An.gambiae s.l. and An. funestus house entry in both villages. Despite significant reductions in vector density and malaria transmission caused by high coverage of ITNs, high numbers of host-seeking malaria vectors are still found indoors due to house designs that favour mosquito entry. In addition to ITNs and IRS, significant efforts should focus on improving house design to prevent mosquito entry and eliminate indoor malaria transmission
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