Mosquito Life Cycle Research Articles

PREDICTION OF DENGUE FEVER EPIDEMIC SPREADING USING DYNAMICS TRANSMISSION VECTOR MODEL

Increasing number of dengue cases in Surabaya shows that its city has high potential of dengue fever epidemic. Although some policies were designed by Surabaya Health Department, such as fogging and mosquito’s nest eradication, but these efforts still out of target because of inaccurate predictions. Ineffectiveness eradication of dengue fever epidemic is caused by lack of information and knowledge on environmental conditions in Surabaya. Developing spread and prediction system to minimize dengue fever epidemic is necessary to be conducted immediately. Spread and prediction system can improve eradication and prevention accuracy. The transmission dynamics vector simulation will be used as an approach to draw a complex system of mosquito life cycle in which involve a lot of factors. Dynamics transmission model used to build model in mosquito model (oviposition rate and pre adult mosquito), infected and death cases in dengue fever. The model of mosquito and infected population can represent system. The output of this research is website of spread and prediction system of dengue fever epidemics to predict growth rate of Aedes Aegypti mosquito, infected, and death population because of dengue fever epidemics. The deviation of infected population is 0,519. The model of death cases in dengue fever is less precision with the deviation 1,229. Death cases model need improvement by adding some variables that influence to dengue fever death cases. Spread of dengue fever prediction will help the government, health department to decide the best policies in minimizing the spread of dengue fever epidemics.

Computational identification of novel microRNAs and their targets in the malarial vector, Anopheles stephensi.

MicroRNAs are a ~22 nucleotide small non-coding RNAs found in animals, plants and viruses. They regulate key cellular processes by enhancing, degrading or silencing protein coding targets. Currently most of the data on miRNA is available from Drosophila . Given their important post-transcriptional role in several organisms, there is a need to understand the miRNA mediated processes in normal and abnormal conditions. Here we report four novel microRNAs ast - mir - 2502, ast - mir - 2559, ast - mir - 3868 and ast - mir - 9891 in Anopheles stephensi identified from a set of 3,052 transcriptome sequences, showing average minimum free energy of -31.8kcal/mol of duplex formation with mRNA indicating their functional relevance. Phylogenetic study shows conservation of sequence signatures within the Class Insecta. Furthermore, 26 potential targets of these four miRNAs have been predicted that play an important role in the mosquito life-cycle. This work leads to novel leads and experimental possibilities for improved understanding of gene regulatory processes in mosquito.

A spatial individual-based model predicting a great impact of copious sugar sources and resting sites on survival of Anopheles gambiae and malaria parasite transmission.

BackgroundAgent-based modelling (ABM) has been used to simulate mosquito life cycles and to evaluate vector control applications. However, most models lack sugar-feeding and resting behaviours or are based on mathematical equations lacking individual level randomness and spatial components of mosquito life. Here, a spatial individual-based model (IBM) incorporating sugar-feeding and resting behaviours of the malaria vector Anopheles gambiae was developed to estimate the impact of environmental sugar sources and resting sites on survival and biting behaviour.MethodsA spatial IBM containing An. gambiae mosquitoes and humans, as well as the village environment of houses, sugar sources, resting sites and larval habitat sites was developed. Anopheles gambiae behaviour rules were attributed at each step of the IBM: resting, host seeking, sugar feeding and breeding. Each step represented one second of time, and each simulation was set to run for 60 days and repeated 50 times. Scenarios of different densities and spatial distributions of sugar sources and outdoor resting sites were simulated and compared.ResultsWhen the number of natural sugar sources was increased from 0 to 100 while the number of resting sites was held constant, mean daily survival rate increased from 2.5% to 85.1% for males and from 2.5% to 94.5% for females, mean human biting rate increased from 0 to 0.94 bites per human per day, and mean daily abundance increased from 1 to 477 for males and from 1 to 1,428 for females. When the number of outdoor resting sites was increased from 0 to 50 while the number of sugar sources was held constant, mean daily survival rate increased from 77.3% to 84.3% for males and from 86.7% to 93.9% for females, mean human biting rate increased from 0 to 0.52 bites per human per day, and mean daily abundance increased from 62 to 349 for males and from 257 to 1120 for females. All increases were significant (P < 0.01). Survival was greater when sugar sources were randomly distributed in the whole village compared to clustering around outdoor resting sites or houses.ConclusionsIncreases in densities of sugar sources or outdoor resting sites significantly increase the survival and human biting rates of An. gambiae mosquitoes. Survival of An. gambiae is more supported by random distribution of sugar sources than clustering of sugar sources around resting sites or houses. Density and spatial distribution of natural sugar sources and outdoor resting sites modulate vector populations and human biting rates, and thus malaria parasite transmission.

An agent-based model of the population dynamics of Anopheles gambiae.

BackgroundAgent-based models (ABMs) have been used to model the behaviour of individual mosquitoes and other aspects of malaria. In this paper, a conceptual entomological model of the population dynamics of Anopheles gambiae and the agent-based implementations derived from it are described. Hypothetical vector control interventions (HVCIs) are implemented to target specific activities in the mosquito life cycle, and their impacts are evaluated.MethodsThe core model is described in terms of the complete An. gambiae mosquito life cycle. Primary features include the development and mortality rates in different aquatic and adult stages, the aquatic habitats and oviposition. The density- and age-dependent larval and adult mortality rates (vector senescence) allow the model to capture the age-dependent aspects of the mosquito biology. Details of hypothetical interventions are also described.ResultsResults show that with varying coverage and temperature ranges, the hypothetical interventions targeting the gonotrophic cycle stages produce higher impacts than the rest in reducing the potentially infectious female (PIF) mosquito populations, due to their multi-hour mortality impacts and their applicability at multiple gonotrophic cycles. Thus, these stages may be the most effective points of target for newly developed and novel interventions. A combined HVCI with low coverage can produce additive synergistic impacts and can be more effective than isolated HVCIs with comparatively higher coverages. It is emphasized that although the model described in this paper is designed specifically around the mosquito An. gambiae, it could effectively apply to many other major malaria vectors in the world (including the three most efficient nominal anopheline species An. gambiae, Anopheles coluzzii and Anopheles arabiensis) by incorporating a variety of factors (seasonality cycles, rainfall, humidity, etc.). Thus, the model can essentially be treated as a generic Anopheles model, offering an excellent framework for such extensions. The utility of the core model has also been demonstrated by several other applications, each of which investigates well-defined biological research questions across a variety of dimensions (including spatial models, insecticide resistance, and sterile insect techniques).

Larvicidal efficacy of Cryptomeria japonica leaf essential oils against Anopheles gambiae.

BackgroundAlternative insecticidal compounds with mortality effect against mosquito life cycle stages are currently needed. The compounds should be biodegradable and nontoxic to non-targeted insects. Plant based larvicides provide effective control of vector populations. This study explored Cryptomeria japonica leaf essential oil larvicidal potency against Anopheles gambiae sensu stricto.MethodsEssential oils (12.5 to 200 μg/mL) extracted from C. japonica leaves were evaluated against An. gambiae s.s. larvae in both the laboratory and semi field in 6 replicates for each dose. Larval mortality readings were taken at 12, 24, 48, and 72 h post treatment.ResultsC. japonica leaf essential oil yield was 17.06 ± 0.56 mL/kg and 1.60 ± 0.33% (w/w). GC-FID and GC-MS analyses revealed 22 constituents. Essential oil was more effective against An. gambiae s.s. larvae in the laboratory than in semi field trials. Mortality increased with increasing dosages (12.5 to 200 μg/mL) in the laboratory (31.75 to 100%) and semi field trials (17.75 to 99.5%), respectively. The LC50 value ranged from 5.55 to 63.92 μg/mL in the laboratory, and 8.22 to 134.84 μg/mL in semi field conditions, LC90 value ranged from 41.34 to 205.93 μg/mL in the laboratory and 50.92 to 213.11 μg/mL in semi field conditions.ConclusionThis study has demonstrated the potential of C. japonica leaf essential oil to cause mortality effects to An. gambiae s. s. larval populations, however, further studies need to be conducted under field conditions and also with individual active compounds of C. japonica essential oil.

Multi-agent modeling and simulation of Plasmodium falciparum dynamics considering sulfadoxine-pyrimethamine resistance and environmental factors

The appearance of resistant Plasmodium falciparum strains after the application of medication in human populations has generated global concern about the correct use of anti-malaria drugs. One of the challenges in malaria research is to find the correct methods to eradicate current strains while avoiding the appearance of new resistant strains. To recommend methods for malaria control, it is necessary to understand disease transmission and parasite dynamics and take into consideration spatial, temporal and environmental variations. In order to describe these elements, mathematical, stochastic and computational models have been developed. In this work, an agent-based model represents the malaria transmission, in which the defined agents are humans and mosquitoes. The interaction between these two agents is simulated in a spatial setting considering environmental and temporal variations. In particular, the parasite is modeled as a characteristic of both agents, considering mutation and recombination and their effects on drug resistance emergence. On the one hand, the model recreates the gonotrophic cycle of mosquito (Anopheles gambiae) and includes population births and deaths. It also represents the mosquito’s epidemiological states: susceptible, exposed and infected (SEI). On the other hand, the model includes a human population in which sulfadoxine-pyrimethamine is applied as an anti-malarial drug with 100% coverage. Human dynamics also includes births, deaths and migration. Additionally, the represented human epidemiological states in the model are SEIS, in which the reinfection probability depends on the disease exposure history. The interaction between both mosquitoes and humans occurs in a simulated scenario of one square kilometer including environmental conditions that affect the mosquito life cycle. The parasite life cycle is modeled during the interaction between mosquitoes and humans. Due to selection pressure as a consequence of sulfadoxine-pyrimethamine use, strains with fixed resistant mutations at the DHFR and DHPS loci emerge. This is modeled through the emergence of fifteen drug-resistant mutations and the subsequent recombination among alleles, generating mutational pathways developing into more resistant strains. Moreover, super-infection in humans (two genotypes) and mosquitoes (two genotypes - infection and the result of recombination) is represented. Simulations for high transmission parameters are consistent with literature, presenting coherent times for each strain appearance, and showing a mutational pathway under high transmission settings and 100% of drug coverage. Thus, measuring the prevalence of each genotype in the model allows the analysis of different cases to eradicate the disease by teh correct usage of control strategies. Furthermore, the model is being adapted for representing low transmission scenarios.

Impacts of Satellite-Based Rainfall Products on Predicting Spatial Patterns of Rift Valley Fever Vectors*

Abstract Spatiotemporal rainfall variability is a key parameter controlling the dynamics of mosquitoes/vector-borne diseases such as malaria, Rift Valley fever (RVF), or dengue. Impacts from rainfall heterogeneity at small scales (i.e., 1–10 km) on the risk of epidemics (i.e., host bite rate or number of bites per host and per night) must be thoroughly evaluated. A model with hydrological and entomological components for risk prediction of the RVF zoonosis is proposed. The model predicts the production of two mosquito species within a 45 km × 45 km area in the Ferlo region, Senegal. The three necessary steps include 1) best rainfall estimation on a small scale, 2) adequate forcing of a simple hydrological model leading to pond dynamics (ponds are the primary larvae breeding grounds), and 3) best estimate of mosquito life cycles obtained from the coupled entomological model. The sensitivity of the model to the spatiotemporal heterogeneity of rainfall is first tested using high-resolution rain fields from a weather radar. The need for high-resolution rain data is thus demonstrated. Several high-resolution satellite rainfall products are evaluated in the region of interest using a dense rain gauge network. Tropical Rainfall Measuring Mission (TRMM) Multisatellite Precipitation Analysis 3B42, version 6 (TMPA-3B42V6), and 3B42 in real time (TMPA-3B42RT); Global Satellite Mapping of Precipitation (GSMaP) in near–real time (GSMaP-NRT) and Moving Vector with Kalman version (GSMaP-MVK); African Rainfall Estimation Algorithm, version 2.0 (RFE 2.0); Climate Prediction Center (CPC) morphing technique (CMORPH); and Precipitation Estimation from Remotely Sensed Information Using Artificial Neural Networks (PERSIANN) are tested and finally corrected using a probability matching method. The corrected products are then used as forcing to the coupled model over the 2003–10 period. The predicted number and size of ponds and their dynamics are greatly improved compared to the model forced only by a single gauge. A more realistic spatiotemporal distribution of the host bite rate of the RVF vectors is thus expected.

Evaluation of some agricultural waste extracts against mosquito larvae, and some types of microorganisms as insecticidal and antibiotic agents.

Extracts of pomegranate peel and apricot kernel were evaluated against bacteria, fungi and insect. Pomegranate extract appear potency when used against bacteria (Escherichia coli, Pseudomonas aeruginosa, Morganella sp, Micrococcus sp, Staphylococcus aureus), fungi (Fusarium sp., Alternaria alternata, Penicillium sp. And Aspergillus niger) and yeast (Candida albicans), but apricot was effective only on three types of fungi (Fusarium sp, A. alternata and A. niger) but not effective against any type of bacteria and yeast (Candida albicans) at concentrations which used in this study. Evaluation of pomegranate and apricot extracts appear different degree of potency against Culex pipiens larvae, apricot extract more effective than pomegranate extract. The potency was increased when make binary mixture of both extracts. Apricot extract appear also effect on life cycle of mosquitoes by decrease pupation percent and adult emergence percent comparing with control.

Larvicidal and antimicrobial activities of silver nanoparticles synthesized using marine fluorescent pseudomonads

Methods In the present study, marine fluorescent pseudomonads were screened against various human pathogenic bacteria and plant fungal pathogens. An autolyzed cell free culture filtrate of selected isolate was used for the synthesis of silver nano particles and characterized using UV, FTIR, XRD and AFM analysis. The antimicrobial efficiency along with larvicidal activity of the synthesized nanoparticles was carried out by observing the lifecycle of mosquito for 96 hours along with appropriate controls.

Monitoring population and environmental parameters of invasive mosquito species in Europe.

To enable a better understanding of the overwhelming alterations in the invasive mosquito species (IMS), methodical insight into the population and environmental factors that govern the IMS and pathogen adaptations are essential. There are numerous ways of estimating mosquito populations, and usually these describe developmental and life-history parameters. The key population parameters that should be considered during the surveillance of invasive mosquito species are: (1) population size and dynamics during the season, (2) longevity, (3) biting behaviour, and (4) dispersal capacity. Knowledge of these parameters coupled with vector competence may help to determine the vectorial capacity of IMS and basic disease reproduction number (R0) to support mosquito borne disease (MBD) risk assessment. Similarly, environmental factors include availability and type of larval breeding containers, climate change, environmental change, human population density, increased human travel and goods transport, changes in living, agricultural and farming habits (e.g. land use), and reduction of resources in the life cycle of mosquitoes by interventions (e.g. source reduction of aquatic habitats). Human population distributions, urbanisation, and human population movement are the key behavioural factors in most IMS-transmitted diseases. Anthropogenic issues are related to the global spread of MBD such as the introduction, reintroduction, circulation of IMS and increased exposure to humans from infected mosquito bites. This review addresses the population and environmental factors underlying the growing changes in IMS populations in Europe and confers the parameters selected by criteria of their applicability. In addition, overview of the commonly used and newly developed tools for their monitoring is provided.

Agent-based modeling of malaria vectors: the importance of spatial simulation.

BackgroundThe modeling of malaria vector mosquito populations yields great insight into drivers of malaria transmission at the village scale. Simulation of individual mosquitoes as “agents” in a distributed, dynamic model domain may be greatly beneficial for simulation of spatial relationships of vectors and hosts.MethodsIn this study, an agent-based model is used to simulate the life cycle and movement of individual malaria vector mosquitoes in a Niger Sahel village, with individual simulated mosquitoes interacting with their physical environment as well as humans. Various processes that are known to be epidemiologically important, such as the dependence of parity on flight distance between developmental habitat and blood meal hosts and therefore spatial relationships of pools and houses, are readily simulated using this modeling paradigm. Impacts of perturbations can be evaluated on the basis of vectorial capacity, because the interactions between individuals that make up the population- scale metric vectorial capacity can be easily tracked for simulated mosquitoes and human blood meal hosts, without the need to estimate vectorial capacity parameters.ResultsAs expected, model results show pronounced impacts of pool source reduction from larvicide application and draining, but with varying degrees of impact depending on the spatial relationship between pools and human habitation. Results highlight the importance of spatially-explicit simulation that can model individuals such as in an agent-based model.ConclusionsThe impacts of perturbations on village scale malaria transmission depend on spatial locations of individual mosquitoes, as well as the tracking of relevant life cycle events and characteristics of individual mosquitoes. This study demonstrates advantages of using an agent-based approach for village-scale mosquito simulation to address questions in which spatial relationships are known to be important.

Anopheles maculipennis complex-responsible for the re-emergence of malaria in Romania?

Between 2010 and 2012, in Iaui City of Romania 5 species belonging to the complex Anopheles maculipennis were identified by PCR: A. melanoon, A. labranchiae, A.atroparvus, A. messeaeand A. maculipennis sp. The last three species were involved in the transmission of malaria in Romania between 1892 and 1961. The species A. labranchiae was signalled for the first time in Romania, being considered as the main vector of malaria in Europe. The identified samples of Anopheles labranchiae were two stage IV larvae, concluding with the adaptation of the species to the climate of Iaui City. Using a new mathematical model realized and implemented by ourselves, based on the construction of a function of interpolation of Lagrange polynomial type, we realized an extrapolation of the evolution of temperatures for the year 2030, demonstrating the existence of favourable conditions of development of both the vector and the malaria parasite. Therefore, it was a temperature raise by 0.72°C in the whole country, as compared to the period of malaria eradication in Romania, and the extrapolation of the evolution of temperatures in the year 2030 showed a raise by 0.8°C, result which coincides with the prognosis made by prestigious research institutes: NIES, CSIRO, HCCPR, MPIM and NCAR, which show a raise by 0.8-1.7° in 2030. In Iaui City, the prognosis made for 2030 shows an average of 24°C for this year in the spring-summer months, temperature which is ideal for the development of the life cycle of mosquitoes, but also for the development of the parasite inside the vector. Taking into account the fact that Iasi, as a cultural city, hosts many foreign students who are carriers of Plasmodium, coming from malaria endemic areas, and the immigration of the population for work in countries of the African continent, the human reservoir of Plasmodium will be permanently maintained. Correlating the three factors implicated in the transmission of malaria: favourable environmental conditions, presence of the vector and of the human reservoir, we could highlight the growing risk of the re-emergence of malaria in Romania.

The Effect of Temperature on Anopheles Mosquito Population Dynamics and the Potential for Malaria Transmission

The parasites that cause malaria depend on Anopheles mosquitoes for transmission; because of this, mosquito population dynamics are a key determinant of malaria risk. Development and survival rates of both the Anopheles mosquitoes and the Plasmodium parasites that cause malaria depend on temperature, making this a potential driver of mosquito population dynamics and malaria transmission. We developed a temperature-dependent, stage-structured delayed differential equation model to better understand how climate determines risk. Including the full mosquito life cycle in the model reveals that the mosquito population abundance is more sensitive to temperature than previously thought because it is strongly influenced by the dynamics of the juvenile mosquito stages whose vital rates are also temperature-dependent. Additionally, the model predicts a peak in abundance of mosquitoes old enough to vector malaria at more accurate temperatures than previous models. Our results point to the importance of incorporating detailed vector biology into models for predicting the risk for vector borne diseases.

Patterns of phenoloxidase activity in insecticide resistant and susceptible mosquitoes differ between laboratory-selected and wild-caught individuals

BackgroundInsecticide resistance has the potential to alter vector immune competence and consequently affect the transmission of diseases.MethodsUsing both laboratory isogenic strains and field-caught Culex pipiens mosquitoes, we investigated the effects of insecticide resistance on an important component of the mosquito immune system: the phenoloxidase (PO) activity. As infection risk varies dramatically with the age and sex of mosquitoes, allocation to PO immunity was quantified across different stages of the mosquito life cycle.ResultsOur results were consistent in showing that larvae have a higher PO activity than adults, females have a higher PO activity than males, and PO activity declines with adult age. We obtained, however, a marked discrepancy between laboratory and field-collected mosquitoes on the effect of insecticide resistance on PO activity. In the laboratory selected strains we found evidence of strong interactions between insecticide resistance and the age and sex of mosquitoes. In particular, 7 and 14 day old esterase-resistant adult females and acetylcholine-esterase resistant males had significantly higher PO activities than their susceptible counterparts. No such effects were, however, apparent in field-caught mosquitoes.ConclusionsCombined, the field and laboratory-based approaches employed in this study provide a powerful test of the effect of insecticide resistance on PO-mediated immunity. The use of laboratory-selected insecticide-resistant strains is still the most widely used method to investigate the pleiotropic effects of insecticide resistance. Our results suggest that the outcome of these laboratory-selected mosquitoes must be interpreted with caution and, whenever possible, compared with mosquitoes captured from the field.

Intra-annual climate variability and malaria transmission in Nigeria

Abstract This study develops an integrated innovation for malaria early warning systems (MEWS), based on vulnerability monitoring, seasonal climate variability data, and epidemiologic surveillance. The main aim of the study is to examine the relationship between intra-annual climate variability and malaria transmission in Nigeria. For this study, climatic conditions considered suitable for the development of the malaria parasite and its transmission through the mosquito stage of its life cycle are temperatures within the range from 18°C to 32°C. Below 18°C the parasite development decreases significantly, while above 32°C the survival of the mosquito is compromised. Relative humidity greater than 60% is also considered a requirement for the mosquito to survive long enough for the parasite to develop sufficiently to be transmitted to its human host stage. The research findings show that seasonality of climate greatly influences the seasonality of malaria transmission. Specifically, rainfall plays an important role in the distribution and maintenance of breeding sites for the mosquito vector. Rainfall and surface water is required for the egg laying and larval stages of the mosquito life cycle and monthly rainfall above 80 mm is considered a requirement. Also, it is temperature that regulates the development rate of both the mosquito larvae and the malaria parasite (Plasmodium species) within the mosquito host. Relative humidity and temperature play an important role in the survival and longevity of the mosquito vector. This study is in conformity with the findings of the IPCC (2001) that malaria is caused by four distinct species of the Plasmodium parasite, transmitted by mosquitoes of the genus Anopheles, which are most abundant in tropical/subtropical regions, although they are also found in limited numbers in temperate climates.

Appropriate Larval Food Quality and Quantity forAedes albopictus(Diptera: Culicidae)

The Asian tiger mosquito Aedes albopictus (Skuse, 1894) is a globally invasive prominent vector of viral and parasitic pathogens. To soundly guide insecticide use in control programs it is crucial to use standardized test systems under rigorously controlled environmental conditions that allow for comparisons across laboratories. An acute standard test procedure (24 h) for insecticide resistance monitoring of mosquitoes has been published by the World Health Organization in 1998, but a standardized chronic test to monitor sublethal insecticide effects on the life cycle of mosquitoes does not yet exist. As a first step toward a standardized chronic bioassay (half-life-cycle-test), the exclusion of qualitative and quantitative food effects by means of standardized, optimal larval feeding would greatly facilitate inter-laboratory comparisons. Against this background we evaluated food qualities and quantities for the aquatic part of the A. albopictus life cycle under different thermal conditions. Five mg TetraMin (Tetra, Melle, Germany) larva(-1) at 25 degrees C rendered the lowest mortality and large pupae. Our fundamental data on A. albopictus feeding provide an opportunity to standardize experiments and thus support interlaboratory comparisons of studies on the ecotoxicology of this dangerous vector mosquito.

Hosts or habitats: What drives the spatial distribution of mosquitoes?

Understanding the factors that influence the distribution of vectors is critical to assess the risk of disease transmission across landscapes. For mosquitoes, existing spatial models use only habitat elements (hydrologic and floristic) to predict the distribution of disease vectors within the landscape, ignoring the potential importance of the distribution of hosts. We tested the hypothesis that the distribution of hosts would better explain the spatial distribution of mosquitoes than habitat variables using Information Theory and Poisson Regression. We analyzed the abundance of ectotherm‐biting mosquitoes and their hosts from 37 points over a 28‐km2 area in Tuskegee National Forest, Alabama, USA. We compared models built using information regarding habitat, hosts, or both for their ability to explain the abundance of Culex peccator and Culex territans, two mosquito species that specialize on reptiles and amphibians. Models built using both host and habitat information were the best models for both species, suggesting that information regarding the distribution of mosquito hosts greatly improves models of mosquito distributions. Moreover, when differences in habitat makeup among stations were accounted for, mosquitoes were found to be significantly more abundant at locations with greater host abundance. Since most mosquitoes feed on only a limited range of hosts and successful blood feeding is one of the most crucial bottlenecks in the life cycle of mosquitoes, it follows that mosquitoes would aggregate in areas of greatest host density. Habitat influences the availability of suitable larval development sites, and to some extent, distribution of hosts. Our analysis, however, shows that within the landscape the distribution of host animals is a crucial factor in determining the spatial distribution of vectors. This has clear and important implications for determining which areas are at a greater risk for zoonotic arboviruses and is a potentially transformative paradigm for understanding the factors that influence the spatial distribution of disease vectors.

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

BackgroundIndoor 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.MethodsA 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.ResultsIntact 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.ConclusionsWhere 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.

Modelling the introduction of Wolbachia into Aedes aegypti mosquitoes to reduce dengue transmission

Infecting Aedes aegypti mosquitoes with the bacteria Wolbachia has been proposed as an innovative new strategy to reduce the transmission of dengue fever. Field trials are currently being undertaken in Queensland, Australia. However, few mathematical models have been developed to consider the persistence of Wolbachia- infected mosquitoes in the wild. This paper develops a mathematical model to determine the persistence of Wolbachia-infected mosquitoes by considering the competition between Wolbachia-infected and non-Wolbachia mosquitoes. The model has four steady states that are biologically feasible: all mosquitoes dying out, only non-Wolbachia mosquitoes surviving, and two steady states where non-Wolbachia and Wolbachia- infected mosquitoes coexist. The stability of the steady states is determined with respect to the key parameters in the mosquito life cycle. A global sensitivity analysis of the model is also conducted. The results show that the persistence of Wolbachia-infected mosquitoes is dominated by the reproductive rate, death rate, maturation rate and maternal transmission. For the parameter values where Wolbachia persists, it dominates the population, and hence the introduction of Wolbachia has great potential to reduce dengue transmission. doi:10.1017/S1446181112000132

Digital image processing techniques for the identification of the appropriate flood areas for the malaria vector procreation

The present work intends to identify the areas which have appropriate environment for the procreation of the disease vector in the northern part of Labrea municipality, in the state of Amazonas. The environmental conditions found in the study region are highly favorable to the elevate density of mosquitoes and to their procreation in the larvae phase, as it is known that the ideal environment considered to its procreation is the aquatic one, where occurs around 3⁄4 of the mosquito life cycle. The digital image processing techniques have been considered as an important tool to identify these areas and have aided the decision making in the public health segment. In order to achieve the purpose of this work, two approaches were made: the object-oriented analysis classification of an optical image and the proposal of a new methodological approach for the terrain description, resulting from the application of the algorithm called HAND. In this approach, the purpose is to characterize both the water bodies identified during the image classification and the possible flood regions, thus, favorable for the procreation of the Anopheles vector. In the spatial analysis stage, a local spatial regression model was used. As a result, it was concluded that de descriptor terrain model in the flood areas of the study region is an explanatory factor of the malaria incidence in the northern part of Labrea.