Mosquito Net Coverage and Utilisation for Malaria\ud Control in Tanzania\ud

\ud In recent years malaria parasites have developed resistance to the most commonly used antimalarial drugs in Tanzania, posing a major challenge for its control. This has led to frequent changes of malaria treatment guidelines, more recently to expensive, yet more effective arthemether/lumefantrine. The use of insecticide treated mosquito nets (ITNs) and long lasting nets (LLINs) in Tanzania has increased slowly over the past few years. Despite the introduction of a voucher scheme to the vulnerable groups, the proportion of households with at least an ITN/LLIN in the country has not been able to achieve the Abuja Declaration of 60% net coverage. Statistics available on the utilisation of nets do not provide a good estimate of the coverage, because of the different study design used to collect the information. This survey was carried out in 21 districts of Tanzania to determine the coverage and utilisation of insecticide treated nets to provide baseline information of the net requirement to cover every sleeping bed in the country. Specifically, this study aimed to (i) determine the ITN coverage by and its distribution in the country; and (ii) determine knowledge, attitudes and practice of the householders as regards to malaria prevention and control Twenty one districts (one from each region) of Mainland Tanzania were selected for the survey. Selection of the district was random. In each district, two wards were selected, one urban (within the district capital) and one rural or sub‐urban. Households were selected randomly using a table of random numbers. At household level, the head or any adult who represented the head of household was interviewed. A structured pre‐tested questionnaire was used to collect information on knowledge, attitude and practices in malaria control, with emphasis on mosquito net ownership and utilisation. Of the 9549 targeted households, 9166 (96%) participated in the survey. Majority of the respondents (76.8%) were from rural district.The mean household size was 3.9 persons. On average, children <5 years old accounted for 39.3% of the members of the households. Respondents with no formal education accounted for 15.8‐37.4% of the interviewees. Most of them were from Mkuranga (55%), Kigoma‐Ujiji (44.2%) and Newala (37.9%). High literate rates were observed in Arumeru and Moshi districts. The majority of the respondents knew that the mosquito is the vector of the malaria parasite (92.6‐99.4%) and infection is through a mosquito bite (92.7‐99.8%). The knowledge of respondents on malaria transmission was generally high (94.0‐99.0%). The majority of the respondents (95.2%) considered the use of mosquito nets as the most effective way of malaria prevention. However, of these, only 66.7% said to have actually used nets in their life time. Knowledge on the use of mosquito nets in the control of malaria was highest and lowest in Eastern and Central zones, respectively.\ud Seventy‐seven percent (4457/8933) agreed to have the investigator entry into their houses and verify the\ud number of nets owned. On average, 62.9% (5,785/8933) of the households had at least a mosquito net. Majority of the respondents in Northern (76.5%) and Southern (76.5%) zones owned at least a mosquito net. The lowest mosquito net ownership was observed among respondents in Western Zone (39.6%). District‐wise, net ownership was highest in Lindi (94.5%), Kyela (91.3%) Arumeru (86.1%), Ilala (83.1%)\ud and Nyamagana (80.0%). Ownership of net was very low in Kilolo (34.8%), Kigoma (36.5%) and Musoma Rural (41.3%). Of the households with nets, 74.4% were using nets all year round. A larger proportion of respondents in Kilolo (68.5%), Mpwapwa (51.9%), Songea Rural (49.2%) and Shinyanga Rural (46.3%) were only using the nets during the rainy season. Out of 9,166 households visited, 3,610 (39.3%) had at least one under five child. Of these, in 1,939 (53.7%) of the households the child slept under a mosquito net during the previous night. Use of nets in children <5 years was most common in northern zone (74%); followed by eastern (66.9%) and southern zone (61.1%). Districts with the largest proportion of <5 year children sleeping under a mosquito nets were Lindi (90.0%), Kyela (85.2%), Ilala (83.2%) and Arumeru (78.2%). Only about a quarter (27%) of the children <5% in western zone were sleeping under a mosquito net. Lowest net coverage for <5 year was in Kigoma (22.7%), Kilolo (25%) and Bukoba Rural (31.2%). A total of 5,785 (62.9%) owned at least a mosquito net. Of these, 4,219 and 1,566 were from the rural and urban districts, respectively. More households in the urban districts (73.4%) than rural districts (59.7%) owned at least a mosquito net. Likewise, there were more households (64.9%) in the urban districts with <5years children sleeping under mosquito nets than in the rural districts (50.4%). More households in urban (32.8%) than in rural districts (25.1%) had at least one insecticide treated net. The number of households with mosquito nets enough for all members of the households ranged from 18.9% (in Urambo) to 37.4% (in Hanang). Households with at least 50% or more occupants using mosquito nets ranged from 16.4% (in Urambo) to 42.8% (in Arumeru). Districts with the largest proportion of ≥50% of the household members sleeping under mosquito nets were Arumeru (46.9%) and Lindi (46.7%). In Manyoni and Lindi, 3.1% and 5% of the households were found to have more nets than the number of household occupants. Only 9% (801/9196) of the households had all occupants sleeping under a mosquito net. Kyela district had about a quarter (23.9%) of the households with all occupants sleeping under nets. Only 29% of the households had at least one insecticide treated mosquito nets. All nets in 51.4% of the households surveyed were ITNs. The largest proportion of households with ITN was observed in northern zone (40.2%), with Arumeru (46%) and Hanang (44.1%) districts having the highest ITN coverage. The lowest proportion (15.5%) of households with ITN was found in the Western Zone. Districts which had the lowest ITN coverage were Musoma Rural (12.6%), Kigoma‐Ujiji (13.2%), and Shinyanga Rural (14.4%). On average, 90.7% (8,123/8,953) of the respondents would prefer using ITN than having their house sprayed with long lasting residual insecticide. More households in urban (32.8%) than in rural districts (25.1%) had at least an ITN> A total of 1939 children underfives were sleeping under mosquito net (any type). Of these, 1140 (58.8%) were using insecticide treated nets (ITN). Overall, 31.6% of the underfives slept under an insecticide treated net during the previous night. Highest coverage was reported in Kyela (47.7%), Nyamagana (47.7%) and Arumeru (46.4%). Lowest ITN in underfives was reported in Kigoma‐Ujiji (16.0%), Musoma (17.2%) and Urambo (17.7%). In Songea more underfives children were sleeping under ITN (43.6%) than in untreated nets (40.9%). Control of bedbugs, lice, fleas, mites and cockroaches was the major added advantage of using insecticide treated nets. On average, 30.8% and 19.6% of the respondents mentioned cockroach and bedbug control as the main advantage of using ITN, respectively. The majority (52.9%) preferred blue coloured net (Northern=45.6%; Central=59.2%; Eastern=56.4%; Lake= 54.4%; Southern= 60.3%, Western= 58.5%) and Southern Highlands= 49.1%). Other colour preferences were white (29.6%), green (14.1%), black (2.1%) and pink (1.2%). A strong preference for blue mosquito nets was observed among respondents in Musoma (77.3%) and Newala (75.5%) districts. On the other hand, the weakest preference (24.7%) for blue nets was observed among respondents in Arumeru district. The majority of the respondents (82%) preferred rectangular shaped net. A larger percent (61.8%) the respondents preferred to have the map of Tanzania as a national logo to identify nets distributed in the country. On average, 62.7% and 28.8% of the households in Tanzania own at least one mosquito net (any type) and insecticide treated net, respectively. Tanzania expects that ITN coverage of under fives in 2009, after the Under Five Catch‐up Campaign is complete, to be at least 80%. If this is to be achieved, there is a need for concerted effort in scaling up the distribution and demand for long lasting nets throughout the country. Moreover, the planned use of IRS in malaria control, currently considered unpopular should be accompanied by rigorous community health education to avoid resistance from household members.\u

Mathematical Modelling of Mosquito Dispersal in a Heterogeneous Environment.

Mosquito dispersal is a key behavioural factor that affects the persistence and resurgence of several vector-borne diseases. Spatial heterogeneity of mosquito resources, such as hosts and breeding sites, affects mosquito dispersal behaviour and consequently affects mosquito population structures, human exposure to vectors, and the ability to control disease transmission. In this paper, we develop and simulate a discrete-space continuous-time mathematical model to investigate the impact of dispersal and heterogeneous distribution of resources on the distribution and dynamics of mosquito populations. We build an ordinary differential equation model of the mosquito life cycle and replicate it across a hexagonal grid (multi-patch system) that represents two-dimensional space. We use the model to estimate mosquito dispersal distances and to evaluate the effect of spatial repellents as a vector control strategy. We find evidence of association between heterogeneity, dispersal, spatial distribution of resources, and mosquito population dynamics. Random distribution of repellents reduces the distance moved by mosquitoes, offering a promising strategy for disease control

Evaluation of Methods for Sampling the Malaria Vector Anopheles darlingi (Diptera, Culicidae) in Suriname and the Relation With Its Biting Behavior

The effectiveness of CO2-baited and human-baited mosquito traps for the sampling of Anopheles darlingi Root was evaluated and compared with human landing collections in Suriname. Biting preferences of this mosquito on a human host were studied and related to trapping data. Traps used were the Centers for Disease Control and Prevention Miniature Light trap, the BG Sentinel mosquito trap, the Mosquito Magnet Liberty Plus mosquito trap (MM-Plus), and a custom-designed trap. Carbon dioxide and humans protected by a bed net were used as bait in the studies. The number of An. darlingi collected was greater with human landing collections than with all other collection methods. An. darlingi did not show a preference for protected humans over CO2 bait. The BG Sentinel mosquito trap with CO2 or human odor as bait and the MM-Plus proved the best alternative sampling tools for An. darlingi. The BG Sentinel mosquito trap with CO2 or human odor as bait was also very efficient at collecting Culex spp. In a field study on biting preferences of wild An. darlingi, the females showed directional biting behavior (P <0.001), with a majority of females (93.3%) biting the lower legs and feet when approaching a seated human host. Higher efficiency of the closer-to-the-ground collecting MM-Plus and BG Sentinel mosquito trap when compared with the other trapping methods may be a result of a possible preference of this mosquito species for low-level biting. It is concluded that odor-baited sampling systems can reliably collect An. darlingi, but the odor bait needs to be improved, for instance, by including host-specific volatiles, to match live human baits

Project MOSI: rationale and pilot-study results of an initiative to help protect zoo animals from mosquito-transmitted pathogens and contribute data on mosquito spatio–temporal distribution change

Mosquito-borne pathogens pose major threats to both wildlife and human health and, largely as a result of unintentional human-aided dispersal of their vector species, their cumulative threat is on the rise. Anthropogenic climate change is expected to be an increasingly significant driver of mosquito dispersal and associated disease spread. The potential health implications of changes in the spatio-temporal distribution of mosquitoes highlight the importance of ongoing surveillance and, where necessary, vector control and other health-management measures. The World Association of Zoos and Aquariums initiative, Project MOSI, was established to help protect vulnerable wildlife species in zoological facilities from mosquito-transmitted pathogens by establishing a zoo-based network of fixed mosquito monitoring sites to assist wildlife health management and contribute data on mosquito spatio-temporal distribution changes. A pilot study for Project MOSI is described here, including project rationale and results that confirm the feasibility of conducting basic standardized year-round mosquito trapping and monitoring in a zoo environment

Can field-based mosquito feeding assays be used for evaluating transmission-blocking interventions?

A recent meta-analysis of mosquito feeding assays to determine the Plasmodium falciparum transmission potential of naturally infected gametocyte carriers highlighted considerable variation in transmission efficiency between assay methodologies and between laboratories. This begs the question as to whether mosquito feeding assays should be used for the evaluation of transmission-reducing interventions in the field and whether these field-based mosquito assays are currently standardized sufficiently to enable accurate evaluations. Here, we address biological and methodological reasons for the observed variations, discuss whether these preclude the use of field-based mosquito feeding assays in field evaluations of transmission-blocking interventions, and propose how we can maximize the precision of estimates. Altogether, we underscore the significant advantages of field-based mosquito feeding assays in basic malaria research and field trials

A Systematic Review of Mosquito Coils and Passive Emanators: Defining Recommendations for Spatial Repellency Testing Methodologies.

Mosquito coils, vaporizer mats and emanators confer protection against mosquito bites through the spatial action of emanated vapor or airborne pyrethroid particles. These products dominate the pest control market; therefore, it is vital to characterize mosquito responses elicited by the chemical actives and their potential for disease prevention. The aim of this review was to determine effects of mosquito coils and emanators on mosquito responses that reduce human-vector contact and to propose scientific consensus on terminologies and methodologies used for evaluation of product formats that could contain spatial chemical actives, including indoor residual spraying (IRS), long lasting insecticide treated nets (LLINs) and insecticide treated materials (ITMs). PubMed, (National Centre for Biotechnology Information (NCBI), U.S. National Library of Medicine, NIH), MEDLINE, LILAC, Cochrane library, IBECS and Armed Forces Pest Management Board Literature Retrieval System search engines were used to identify studies of pyrethroid based coils and emanators with key-words "Mosquito coils" "Mosquito emanators" and "Spatial repellents". It was concluded that there is need to improve statistical reporting of studies, and reach consensus in the methodologies and terminologies used through standardized testing guidelines. Despite differing evaluation methodologies, data showed that coils and emanators induce mortality, deterrence, repellency as well as reduce the ability of mosquitoes to feed on humans. Available data on efficacy outdoors, dose-response relationships and effective distance of coils and emanators is inadequate for developing a target product profile (TPP), which will be required for such chemicals before optimized implementation can occur for maximum benefits in disease control

Characterization of a broad-based mosquito yeast interfering RNA larvicide with a conserved target site in mosquito semaphorin-1a genes

BACKGROUND: RNA interference (RNAi), which has facilitated functional characterization of mosquito neural development genes such as the axon guidance regulator semaphorin-1a (sema1a), could one day be applied as a new means of vector control. Saccharomyces cerevisiae (baker's yeast) may represent an effective interfering RNA expression system that could be used directly for delivery of RNA pesticides to mosquito larvae. Here we describe characterization of a yeast larvicide developed through bioengineering of S. cerevisiae to express a short hairpin RNA (shRNA) targeting a conserved site in mosquito sema1a genes. RESULTS: Experiments conducted on Aedes aegypti larvae demonstrated that the yeast larvicide effectively silences sema1a expression, generates severe neural defects, and induces high levels of larval mortality in laboratory, simulated-field, and semi-field experiments. The larvicide was also found to induce high levels of Aedes albopictus, Anopheles gambiae and Culex quinquefasciatus mortality. CONCLUSIONS: The results of these studies indicate that use of yeast interfering RNA larvicides targeting mosquito sema1a genes may represent a new biorational tool for mosquito control

Distribution of mosquito larvae in rice field habitats: A spatial scale analysis in semi-field condition

The distribution of the mosquito larvae in the breeding habitats varies at the spatial scale depending on the&nbsp;availability of the resources and the predators. This proposition was assessed through the observation of the&nbsp;spatial distribution of Culex larvae (Culex tritaeniorhynchus) in artificially constructed rice field habitats. Using a&nbsp;binomial generalized linear model with logit link, the disparity in the abundance of the larvae was evaluated to&nbsp;justify the effects of light (light vs shade), vertical (surface vs bottom), and horizontal (wall vs center) distribution&nbsp;as explanatory variables. Under light availability, the spatial occupancy of the mosquito larvae was higher in&nbsp;the center than in the walls of the mesocosms. However, the larval orientation was higher on the surface than at&nbsp;the bottom of the mesocosms in all instances. In comparison to open spaces, the larval aggregation was higher&nbsp;in the presence of the floating vegetations like Azolla and Lemna, indicating that the habitat heterogeneity of the&nbsp;mesocosms influenced the distribution of the mosquito larvae in the available spaces. A reduction in the larval&nbsp;aggregation pattern in the spaces was observed in the presence of the predator (Anisops sp.) reflecting the&nbsp;possible evasion tactics of the mosquito larvae. The observations suggest that the mosquito larvae may utilize&nbsp;the vegetation in the rice field habitats quite effectively and occupy empty spaces of predators. The results may&nbsp;be considered as a prototype of the prospective localization of the mosquito larvae in the rice fields and help to&nbsp;frame the strategies of spraying the biopesticides to achieve optimal efficacy in mosquito regulation

Live calcium imaging of Aedes aegypti neuronal tissues reveals differential importance of chemosensory systems for life-history-specific foraging strategies.

BackgroundThe mosquito Aedes aegypti has a wide variety of sensory pathways that have supported its success as a species as well as a highly competent vector of numerous debilitating infectious pathogens. Investigations into mosquito sensory systems and their effects on behavior are valuable resources for the advancement of mosquito control strategies. Numerous studies have elucidated key aspects of mosquito sensory systems, however there remains critical gaps within the field. In particular, compared to that of the adult form, there has been a lack of studies directed towards the immature life stages. Additionally, although numerous studies have pinpointed specific sensory receptors as well as responding motor outputs, there has been a lack of studies able to monitor both concurrently.ResultsTo begin filling aforementioned gaps, here we engineered Ae. aegypti to ubiquitously express a genetically encoded calcium indicator, GCaMP6s. Using this strain, combined with advanced microscopy, we simultaneously measured live stimulus-evoked calcium responses in both neuronal and muscle cells with a wide spatial range and resolution.ConclusionsBy coupling in vivo live calcium imaging with behavioral assays we were able to gain functional insights into how stimulus-evoked neural and muscle activities are represented, modulated, and transformed in mosquito larvae enabling us to elucidate mosquito sensorimotor properties important for life-history-specific foraging strategies