Assessment of larval and pupal indices of dengue mosquito vectors in a North-Eastern state of Tripura, India.

BACKGROUND OBJECTIVES: Dengue is a major vector-borne disease having public health importance. It is caused by Dengue Virus (DENV) and is transmitted by mosquitoes of Aedes species. With the unavailability of a vaccine, vector control remains the only preventive measure for dengue. Studies have already been conducted to establish the presence of dengue vectors in the north-eastern states of India. However, limited studies have been conducted in Tripura state. In the present study we aimed to identify the preferred breeding habitats of dengue vectors in the state. METHODS: Clinical case data of dengue since the last five years was studied and the areas with the highest case numbers were identified. Entomological investigation was carried out in areas reporting the highest number of cases. Larvae were collected from the breeding habitats using standard protocol followed by morphological and molecular identification. Further, House index (HI), Container index (CI) and Pupal index (PI) were determined. The positive pools were then processed for incrimination for the presence of dengue virus. Calculation of entomological indices was done. RESULTS: Of the total 815 containers searched, 36.80% containers were positive for mosquito larvae. Among the immature mosquito collection, 836 adults emerged and were identified as Aedes albopictus using standard taxonomic keys followed by molecular methods. HI, CI and PI, varied from 15.38% to 100%, 21% to 31.04 %, and 2.93% to 110.53% respectively. However, none of the pools was positive for dengue virus. INTERPRETATION CONCLUSION: The present study identified Ae. albopictus as a potential vector of dengue in Tripura. The study gave important insights on the preferred larval habitats and provides information on the indication of displacement of Ae. albopictus from rural to urban and semi-urban areas. However, longitudinal studies for longer time frame are necessary for any conclusive remarks.

Statewide Efficacy Assessment of Insect Growth Regulators Against Aedes albopictus (Diptera: Culicidae) in Sabah, Malaysia: An Alternative Control Strategy?

The efficacy of three groups of insect growth regulators, namely juvenile hormone mimics (methoprene and pyriproxyfen), chitin synthesis inhibitors (diflubenzuron and novaluron), and molting disruptor (cyromazine) was evaluated for the first time, against Aedes albopictus Skuse (Diptera: Culicidae) larvae from 14 districts in Sabah, Malaysia. The results showed that all field populations of Ae. albopictus were susceptible towards methoprene, pyriproxyfen, diflubenzuron, novaluron, and cyromazine, with resistance ratio values ranging from 0.50-0.90, 0.60-1.00, 0.67-1.17, 0.71-1.29, and 0.74-1.07, respectively. Overall, the efficacy assessment of insect growth regulators in this study showed promising outcomes and they could be further explored as an alternative to conventional insecticides.

Aedes albopictus bionomics data collection by citizen participation on Procida Island, a promising Mediterranean site for the assessment of innovative and community-based integrated pest management methods.

In the last decades, the colonization of Mediterranean Europe and of other temperate regions by Aedes albopictus created an unprecedented nuisance problem in highly infested areas and new public health threats due to the vector competence of the species. The Sterile Insect Technique (SIT) and the Incompatible Insect Technique (IIT) are insecticide-free mosquito-control methods, relying on mass release of irradiated/manipulated males, able to complement existing and only partially effective control tools. The validation of these approaches in the field requires appropriate experimental settings, possibly isolated to avoid mosquito immigration from other infested areas, and preliminary ecological and entomological data. We carried out a 4-year study in the island of Procida (Gulf of Naples, Italy) in strict collaboration with local administrators and citizens to estimate the temporal dynamics, spatial distribution, and population size of Ae. albopictus and the dispersal and survival of irradiated males. We applied ovitrap monitoring, geo-spatial analyses, mark-release-recapture technique, and a citizen-science approach. Results allow to predict the seasonal (from April to October, with peaks of 928-9,757 males/ha) and spatial distribution of the species, highlighting the capacity of Ae. albopictus population of Procida to colonize and maintain high frequencies in urban as well as in sylvatic inhabited environments. Irradiated males shown limited ability to disperse (mean daily distance travelled <60m) and daily survival estimates ranging between 0.80 and 0.95. Overall, the ecological characteristics of the island, the acquired knowledge on Ae. albopictus spatial and temporal distribution, the high human and Ae. albopictus densities and the positive attitude of the resident population in being active parts in innovative mosquito control projects provide the ground for evidence-based planning of the interventions and for the assessment of their effectiveness. In addition, the results highlight the value of creating synergies between research groups, local administrators, and citizens for affordable monitoring (and, in the future, control) of mosquito populations.

The effect of demographic and environmental variability on disease outbreak for a dengue model with a seasonally varying vector population.

Seasonal changes in temperature, humidity, and rainfall affect vector survival and emergence of mosquitoes and thus impact the dynamics of vector-borne disease outbreaks. Recent studies of deterministic and stochastic epidemic models with periodic environments have shown that the average basic reproduction number is not sufficient to predict an outbreak. We extend these studies to time-nonhomogeneous stochastic dengue models with demographic variability wherein the adult vectors emerge from the larval stage vary periodically. The combined effects of variability and periodicity provide a better understanding of the risk of dengue outbreaks. A multitype branching process approximation of the stochastic dengue model near the disease-free periodic solution is used to calculate the probability of a disease outbreak. The approximation follows from the solution of a system of differential equations derived from the backward Kolmogorov differential equation. This approximation shows that the risk of a disease outbreak is also periodic and depends on the particular time and the number of the initial infected individuals. Numerical examples are explored to demonstrate that the estimates of the probability of an outbreak from that of branching process approximations agree well with that of the continuous-time Markov chain. In addition, we propose a simple stochastic model to account for the effects of environmental variability on the emergence of adult vectors from the larval stage.

Development of an Alternative Low-Cost Larval Diet for Mass Rearing of Aedes aegypti Mosquitoes.

BACKGROUND: Aedes aegypti is a major vector of arboviruses that may be controlled on an area-wide basis, using novel approaches such as Sterile Insect Technique (SIT) and Incompatible Insect Technique (IIT). Larval diet is a critical factor to be considered in mass rearing of Aedes mosquitoes for SIT and IIT programs. Therefore, the current study is aimed at evaluating the effects of two novel diets developed from dry fish powder on the growth and development of immature stages and adult fitness-related characteristics of Ae. aegypti in Sri Lanka. METHOD: Three batches of the first instar Ae. aegypti larva, each containing 250 larvae, were exposed to three different larval diets as standard dry fish powder (D1), dry fish powder meal and brewer's yeast (D2), and International Atomic Energy Agency- (IAEA-) recommended diet (D3), separately. Morphometric and developmental parameters of the 4th instar larvae, pupae, and adult mosquitoes reared under different dietary treatments were measured. The entire experimental setup was replicated thrice. A General Linear Model (GLM) in the form of two-way ANOVA was used for the statistical analysis. RESULTS: Significant diet-based variations were observed in the head length, head width, thoracic length, thoracic width, abdominal length, abdominal width, and total length (F 2,87 > 4.811; P < 0.05) of Ae. aegypti larvae. The highest pupation success and the larval size were observed from the larvae fed the D2 diet, while the lowest was reported from D1. All adult morphometric parameters of adult male and female Ae. aegypti mosquitoes also denoted significant dietary variations, reporting the best-sized adults from the D2 diet (F 2,87 > 3.54; P < 0.05). Further, significantly higher fecundity and male longevity were also shown by the adult Ae. aegypti (F 2,6 > 7.897; P < 0.01) mosquitoes reared under diet D2. CONCLUSION: Based on all the growth and developmental parameters, the D2 diet tends to perform similar to the IAEA-recommended diet in mass rearing of Ae. aegypti mosquitoes, while being more inexpensive. Therefore, larval diet D2 could be suggested as the ideal diet for mass rearing of Ae. aegypti for IIT and SIT-based vector control in Sri Lanka.

Comparison of climatic factors on mosquito abundance at US Army Garrison Humphreys, Republic of Korea.

INTRODUCTION: A number of studies have been conducted on the relationship between the distribution of mosquito abundance and meteorological variables. However, few studies have specifically provided specific ranges of temperatures for estimating the maximum abundance of mosquitoes as an empirical basis for climatic dynamics for estimating mosquito-borne infectious disease risks. METHODS: Adult mosquitoes were collected for three consecutive nights/week using Mosquito Magnet® Independence® model traps during 2018 and 2019 at US Army Garrison (USAG) Humphreys, Pyeongtaek, Gyeonggi Province, Republic of Korea (ROK). An estimate of daily mean temperatures (provided by the Korea Meteorological Administration) were distributed at the maximum abundance for selected species of mosquitoes using daily mosquito collection data after controlling for mosquito ecological cycles and environmental factors. RESULTS: Using the Monte-Carlo simulation, the overall mosquito population abundance peaked at 22.7°C (2.5th-97.5th: 21.7°C-23.8°C). Aedes albopictus, vector of Zika, chikungunya, dengue fever and other viruses, abundance peaked at 24.6°C (2.5th-97.5th, 22.3°C-25.6°C), while Japanese encephalitis virus (JEV) vectors, e.g., Culex tritaeniorhynchus and Culex pipiens, peaked at 24.3°C (2.5th-97.5th: 21.9°C-26.3°C) and 22.6°C (2.5th-97.5th: 21.9°C-25.2°C), respectively. Members of the Anopheles Hyrcanus Group, some of which are vivax malaria vectors in the ROK, abundance peaked at 22.4°C (2.5th-97.5th: 21.5°C-23.8°C). CONCLUSION: The empirical mean temperature ranges for maximum abundance were determined for each mosquito species collected at USAG Humphreys. These data contributed to the identification of relative mosquito abundance patterns for estimating mosquito-borne disease risks and developing and implementing disease prevention practices.

Pragmatic selection of larval mosquito diets for insectary rearing of Anopheles gambiae and Aedes aegypti.

Larval mosquitoes are aquatic omnivorous scavengers which scrape food from submerged surfaces and collect suspended food particles with their mouth brushes. The composition of diets that have been used in insectaries varies widely though necessarily provides sufficient nutrition to allow colonies to be maintained. Issues such as cost, availability and experience influence which diet is selected. One component of larval diets, essential fatty acids, appears to be necessary for normal flight though deficiencies may not be evident in laboratory cages and are likely more important when mosquitoes are reared for release into the field in e.g. mark-release-recapture and genetic control activities. In this study, four diets were compared for rearing Anopheles gambiae and Aedes aegypti, all of which provide these essential fatty acids. Two diets were custom formulations specifically designed for mosquitoes (Damiens) and two were commercially available fish foods: Doctors Foster and Smith Koi Staple Diet and TetraMin Plus Flakes. Development rate, survival, dry weight and adult longevity of mosquitoes reared with these four diets were measured. The method of presentation of one diet, Koi pellets, was additionally fed in two forms, pellets or a slurry, to determine any effect of food presentation on survival and development rate. While various criteria might be selected to choose 'the best' food, the readily-available Koi pellets resulted in development rates and adult longevity equal to the other diets, high survival to the adult stage and, additionally, this is available at low cost.

Toxic assessment, growth disrupting and neurotoxic effects of red seaweeds' botanicals against the dengue vector mosquito Aedes aegypti L.

Application of synthetic pesticides over decades to control insects, pests, and disease vectors has resulted in negative impacts on environment and health. The current study assessed the toxicological effects of 12 botanicals obtained from 4 different red seaweeds against the dengue vector mosquito Aedes aegypti L. (Diptera: Culicidae). Four species of red seaweeds, namely Laurencia karachiana, Gracilaria foliifera, Jania rubens, Asparagopsis taxiformis, were collected from Karachi coast and extracted with hexane, dichloromethane and methanol. The efficiency of these extracts was determined by using a dose-response bioassay method against 4th instar larvae of Ae. aegypti. Separate investigations on the toxicity and IGI effects were done. Comparative studies showed that the hexane extracts induced more toxic effects. Based on the LC50 values, obtained after 24 h of treatments, hexane extract of J. rubens (HJ) exhibited toxic effects with LC50 32 µg/mL, (equivalent to GHS category 3), followed by G. foliifera (HG) (LC50 76.8 µg/mL). HJ also showed prominent neurotoxic effects within 1-6 h. Comparatively, higher morphological abnormalities and growth inhibiting (IGI) effects were obtained in the dichloromethane and methanol extracts treated larvae, after 48-96 h, resulting in the formation of immature life forms such as larvi-pupae and pupi-adult. Presumptive growth inhibiting effects were also noted. These included formation of albino and black pupae, deformities in the internal structure of the treated larvae and the chitin synthesis related effects such as 'inhibiting effect on adult emergence'. Finding revealed that red seaweeds, harvested from the Arabian Sea, have potentials to affect Ae. aegypti survival and thus can be utilized as green pesticides.

Reducing the cost and assessing the performance of a novel adult mass-rearing cage for the dengue, chikungunya, yellow fever and Zika vector, Aedes aegypti (Linnaeus).

INTRODUCTION: The widespread emergence of resistance to insecticides used to control adult Aedes mosquitoes has made traditional control strategies inadequate for the reduction of various vector populations. Therefore, complementary vector control methods, such as the Sterile Insect Technique, are needed to enhance existing efforts. The technique relies on the rearing and release of large numbers of sterile males, and the development of efficient and standardized mass-rearing procedures and tools is essential for its application against medically important mosquitoes. METHODS: In the effort to reduce the cost of the rearing process, a prototype low-cost plexiglass mass-rearing cage has been developed and tested for egg production and egg hatch rate in comparison to the current Food and Agriculture Organization/International Atomic Energy Agency (FAO/IAEA) stainless-steel cage. Additionally, an adult-index was validated and used as a proxy to estimate the mosquito survival rates by counting the number of male and female mosquitoes that were resting within each of the 6 squares at a given point of time each day in the cage. RESULTS: The study has shown that the prototype mass-rearing cage is cheap and is as efficient as the FAO/IAEA stainless-steel cage in terms of egg production, with even better overall egg hatch rate. The mean numbers of eggs per cage, after seven cycles of blood feeding and egg collection, were 969,789 ± 138,101 and 779,970 ± 123,042, corresponding to 81 ± 11 and 65 ± 10 eggs per female over her lifespan, in the prototype and the stainless-steel-mass-rearing cages, respectively. The longevity of adult male and female mosquitoes was not affected by cage type and, the adult-index could be considered as an appropriate proxy for survival. Moreover, the mass-rearing cage prototype is easy to handle and transport and improves economic and logistic efficiency. CONCLUSION: The low-cost mass-rearing prototype cage can be recommended to produce Ae. aegypti in the context of rear and release techniques. The proposed adult-index can be used as a quick proxy of mosquito survival rates in mass-rearing settings.

Entomological assessment of dengue virus transmission risk in three urban areas of Kenya.

Urbanization is one of the major drivers of dengue epidemics globally. In Kenya, an intriguing pattern of urban dengue virus epidemics has been documented in which recurrent epidemics are reported from the coastal city of Mombasa, whereas no outbreaks occur in the two major inland cities of Kisumu and Nairobi. In an attempt to understand the entomological risk factors underlying the observed urban dengue epidemic pattern in Kenya, we evaluated vector density, human feeding patterns, vector genetics, and prevailing environmental temperature to establish how these may interact with one another to shape the disease transmission pattern. We determined that (i) Nairobi and Kisumu had lower vector density and human blood indices, respectively, than Mombasa, (ii) vector competence for dengue-2 virus was comparable among Ae. aegypti populations from the three cities, with no discernible association between susceptibility and vector cytochrome c oxidase subunit 1 gene variation, and (iii) vector competence was temperature-dependent. Our study suggests that lower temperature and Ae. aegypti vector density in Nairobi may be responsible for the absence of dengue outbreaks in the capital city, whereas differences in feeding behavior, but not vector competence, temperature, or vector density, contribute in part to the observed recurrent dengue epidemics in coastal Mombasa compared to Kisumu.

The ecological and epidemiological consequences of reproductive interference between the vectors Aedes aegypti and Aedes albopictus.

Vector ecology is integral to understanding the transmission of vector-borne diseases, with processes such as reproduction and competition pivotal in determining vector presence and abundance. The arbovirus vectors Aedes aegypti and Aedes albopictus compete as larvae, but this mechanism is insufficient to explain patterns of coexistence and exclusion. Inviable interspecies matings-known as reproductive interference-is another candidate mechanism. Here, we analyse mathematical models of mosquito population dynamics and epidemiology which include two Aedes-specific features of reproductive interference. First, as these mosquitoes use hosts to find mates, reproductive interference will only occur if the same host is visited. Host choice will, in turn, be determined by behavioural responses to host availability. Second, females can become sterilized after mis-mating with heterospecifics. We find that a species with an affinity for a shared host will suffer more from reproductive interference than a less selective competitor. Costs from reproductive interference can be 'traded-off' against costs from larval competition, leading to competitive outcomes that are difficult to predict from empirical evidence. Sterilizations of a self-limiting species can counterintuitively lead to higher densities than a competitor suffering less sterilization. We identify that behavioural responses and reproductive interference mediate a concomitant relationship between vector ecological dynamics and epidemiology. Competitors with opposite behavioural responses can maintain disease where human hosts are rare, due to vector coexistence facilitated by a reduced cost from reproductive interference. Our work elucidates the relative roles of the competitive mechanisms governing Aedes populations and the associated epidemiological consequences.

In vitro and in vivo toxicity assessment of selenium nanoparticles with significant larvicidal and bacteriostatic properties.

In the present study, we investigated the larvicidal and bacteriostatic activity of biosynthesized selenium nanoparticles using aqueous berry extract of Murraya koenigii (Mk-Se NPs). The synthesized Mk-Se NPs were characterized using UV-visible spectroscopy, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis. XRD analysis revealed the crystalline nature of Mk-Se NPs as hexagonal. The FTIR spectra of Mk-Se NPs exhibited a strong peak at 3441 cm-1 corresponding to the OH group. SEM and TEM analysis showed that the Mk-Se NPs were spherical in shape with a size between 50 and 150 nm. EDX peaks confirm the presence of 73.38% of selenium and 26.62% of oxide in Mk-Se NPs. Mk-Se NPs showed significant larvicidal property against the 4th instar larvae of a dengue fever-causing vector Aedes aegypti with LC50- - 3.54 µg mL-1 and LC90- - 8.128 µg mL-1 values. Mk-Se NPs displayed anti-bacterial activity against Gram-positive (Enterococcus faecalis &Streptococcus mutans) and Gram-negative (Shigella sonnei &Pseudomonas aeruginosa) bacteria at 40 and 50 µg mL-1. In addition, Mk-Se NPs reduced bacterial biofilm thickness extensively at 25 µg mL-1. The high antioxidant property at 50 µg mL-1 and low hemolysis activity till 100 µg mL-1 proved the biocompatible nature of Mk-Se NPs. In vitro and in vivo toxicity assessment of Mk-Se NPs showed low cytotoxicity against RAW 264.7 macrophages and Artemia nauplii. Together, our results suggest the potential application of Mk-Se NPs as a nano-biomedicine.

Isolation and growth inhibition potential of entomopathogenic nematodes against three public health important mosquito vectors.

The prevalence of mosquito vector borne diseases and the resistance of mosquitoes to conventional pesticides have been of important public concern to the mosquito endemic countries. Present study was conducted to identify the native bio-larvicidal potential of the entomopathogenic nematodes; Steinernema siamkayai (KPR-4) Heterohabditis indica (KPR-8), Steinernema glaseri and Steinernema abbasi. The isolated nematodes were subsequently cultured and evaluated their larvicidal potential against the larvae of Aedes aegypti, Anopheles stephensi and Culex quinquefasciatus. Among the tested four different nematode species, the S. abassi exerted the highest mortality against A. aegypti (97.33%), the H. indica (KPR-8) against A. stephensi (97.33%) and the S. siamkayai (KPR-4) against C. quinquefasciatus (98.67%). The maximal mosquito-larvicidal property of EPNs was found with the LC50 and LC90 values (IJs/larvae): S. abbasi = 12.47 & 54.35 on A. aegypti; H. indica KPR-8 = 19.88 & 66.81 on A. stephensi and S. siamkayai KPR-4 = 16.69 & 58.97 on C. quinquefasciatus, respectively. The presently generated data on the molecular and larvicidal characteristics of the entomopathogenic nematodes form an important baseline data that upon further research would lead to the development of eco-friendly mosquito-control agent.

Novel larvicide tablets of Bacillus thuringiensis var. israelensis: Assessment of larvicidal effect on Aedes aegypti (Diptera: Culicidae) in Colombia.

INTRODUCTION: Aedes (Stegomyia) aegypti is the vector for dengue, chikungunya, and Zika arboviruses. Bti-CECIF is a bioinsecticide designed and developed in the form of a solid tablet for the control of this vector. It contains Bacillus thuringiensis var. israelensis (Bti) serotype H-14. OBJECTIVE: To evaluate under semi-field and field conditions the efficacy and residual activity of Bti-CECIF tablets on Aedes aegypti larvae in two Colombian municipalities. MATERIALS AND METHODS: We tested under semi-field conditions in plastic tanks (Rotoplast™) four different Bti doses (0.13, 0.40, 0.66 and 0.93 mg/L) in the municipality of Apartadó, department of Antioquia, to assess Bti-CECIF efficacy (percentage of reduction of larval density) and the residual activity in water tanks containing A. aegypti third-instar larvae. The efficacy and residuality of the most lethal dose were subsequently evaluated under field conditions in cement tanks in the municipality of San Carlos, department of Córdoba. RESULTS: Under semi-field conditions, the highest tested dose exhibited the greatest residual activity (15 days) after which larval mortality was 80%. Under field conditions, the highest tested Bti-CECIF doses showed 100% mortality and exhibited a residual activity of seven days in 90% of the tanks. CONCLUSION: Bti-CECIF tablets effectively controlled A. aegypti larvae under field conditions for up to seven days post-treatment.

Assessment of insecticide resistance in primary dengue vector, Aedes aegypti (Linn.) from Northern Districts of West Bengal, India.

Aedes mosquitoes are the major vectors transmitting several arboviral diseases such as dengue, zika and chikungunya worldwide. Northern districts of West Bengal is home to several epidemics vectored by mosquito including dengue infections, proper control of which depends on efficient vector control. However the onset of insecticide resistance has resulted in failure of vector control approaches. This study was carried out to unveil the level of insecticide resistance prevailing among the primary dengue vector in this dengue endemic region of India. It was observed that, field caught populations of Ae. aegypti were moderately to severely resistant to majority of the insecticide classes tested, i.e. Organochlorine (DDT), Organophosphates (temephos, malathion), Synthetic Pyrethroids (deltamethrin, lambdacyhalothrin and permethrin) and carbamate (propoxur). In majority of the populations, metabolic detoxification seemed to play the underlying role behind the development of insecticide resistance. This study seems to be the first report revealing the pattern of insecticide resistance in Ae. aegypti from Northern West Bengal. Efficient disease management in this region can only be achieved through proper insecticide resistance management. This study may help the concerned authorities in the formulation of an effective vector control strategy throughout this region incorporating the knowledge gained through this study.

Assessment of Aedes albopictus reference genes for quantitative PCR at different stages of development.

Members of the Aedes genus of mosquitoes are widely recognized as vectors of viral diseases. Ae.albopictus is its most invasive species, and are known to carry viruses such as Dengue, Chikugunya and Zika. Its emerging importance puts Ae.albopictus on the forefront of genetic interaction and evolution studies. However, a panel of suitable reference genes specific for this insect is as of now undescribed. Nine reference genes, namely ACT, eEF1-γ, eIF2α, PP2A, RPL32, RPS17, PGK1, ILK and STK were evaluated. Expression patterns of the candidate reference genes were observed in a total of seventeen sample types, separated by stage of development and age. Gene stability was inferred from obtained quantification data through three widely cited evaluation algorithms i.e. BestKeeper, geNorm, and NormFinder. No single gene showed a satisfactory degree of stability throughout all developmental stages. Therefore, we propose combinations of PGK and ILK for early embryos; RPL32 and RPS17 for late embryos, all four larval instars, and pupae samples; eEF1-γ with STK for adult males; eEF1-γ with RPS17 for non-blood fed females; and eEF1-γ with eIF2α for both blood-fed females and cell culture. The results from this study should be able to provide a more informed selection of normalizing genes during qPCR in Ae.albopictus.

Socioeconomic and Human Behavioral Factors Associated With Aedes aegypti (Diptera: Culicidae) Immature Habitat in Tucson, AZ.

Aedes aegypti (L.; Diptera: Culicidae) has been established in the southwestern United States for several decades, but relationships between humans and mosquitoes in this arid region are not well-characterized. In August 2012, the outdoor premises of 355 houses within 20 neighborhoods in Tucson, Arizona were surveyed for containers that could provide larval habitat for Ae. aegypti mosquitoes. At the same time, a knowledge, attitudes and practices (KAP) questionnaire was administered to a resident of each house surveyed for immature mosquitoes. The KAP questionnaire assessed respondents' knowledge and concerns about vector-borne illnesses as well as practices they used to avoid mosquitoes. Of the houses surveyed, 91% had at least one container present, and 64% had at least one container with standing water. On average, each house had 2.2 containers with water at the time of the survey. The overall House Index (proportion of premises surveyed with at least one container with Ae. aegypti immatures present) was 13%. Based on questionnaire responses, there was a significant positive association between the number of residents in the home and the odds of finding Ae. aegypti positive containers on the premises, while household income showed a significant negative association. The reported frequency of checking for standing water was also significantly associated with the odds of finding immatures, although the nature of this association was ambiguous. Flower pots were the principal type of container with Ae. aegypti larvae. These findings show that larval habitat is widely available even in an arid environment and city with good housing and sanitation infrastructure.

Assessment of risk of dengue and yellow fever virus transmission in three major Kenyan cities based on Stegomyia indices.

Dengue (DEN) and yellow fever (YF) are re-emerging in East Africa, with contributing drivers to this trend being unplanned urbanization and increasingly adaptable anthropophilic Aedes (Stegomyia) vectors. Entomological risk assessment of these diseases remains scarce for much of East Africa and Kenya even in the dengue fever-prone urban coastal areas. Focusing on major cities of Kenya, we compared DEN and YF risk in Kilifi County (DEN-outbreak-prone), and Kisumu and Nairobi Counties (no documented DEN outbreaks). We surveyed water-holding containers for mosquito immature (larvae/pupae) indoors and outdoors from selected houses during the long rains, short rains and dry seasons (100 houses/season) in each County from October 2014-June 2016. House index (HI), Breteau index (BI) and Container index (CI) estimates based on Aedes (Stegomyia) immature infestations were compared by city and season. Aedes aegypti and Aedes bromeliae were the main Stegomyia species with significantly more positive houses outdoors (212) than indoors (88) (n = 900) (χ2 = 60.52, P < 0.0001). Overall, Ae. aegypti estimates of HI (17.3 vs 11.3) and BI (81.6 vs 87.7) were higher in Kilifi and Kisumu, respectively, than in Nairobi (HI, 0.3; BI,13). However, CI was highest in Kisumu (33.1), followed by Kilifi (15.1) then Nairobi (5.1). Aedes bromeliae indices were highest in Kilifi, followed by Kisumu, then Nairobi with HI (4.3, 0.3, 0); BI (21.3, 7, 0.7) and CI (3.3, 3.3, 0.3), at the respective sites. HI and BI for both species were highest in the long rains, compared to the short rains and dry seasons. We found strong positive correlations between the BI and CI, and BI and HI for Ae. aegypti, with the most productive container types being jerricans, drums, used/discarded containers and tyres. On the basis of established vector index thresholds, our findings suggest low-to-medium risk levels for urban YF and high DEN risk for Kilifi and Kisumu, whereas for Nairobi YF risk was low while DEN risk levels were low-to-medium. The study provides a baseline for future vector studies needed to further characterise the observed differential risk patterns by vector potential evaluation. Identified productive containers should be made the focus of community-based targeted vector control programs.

The elimination of the dengue vector, Aedes aegypti, from Brisbane, Australia: The role of surveillance, larval habitat removal and policy.

Aedes aegypti (L.) (Diptera: Culicidae) is a highly invasive mosquito whose global distribution has fluctuated dramatically over the last 100 years. In Australia the distribution of Ae. aegypti once spanned the eastern seaboard, for 3,000 km north to south. However, during the 1900s this distribution markedly reduced and the mosquito disappeared from its southern range. Numerous hypotheses have been proffered for this retraction, however quantitative evidence of the mechanisms driving the disappearance are lacking. We examine historical records during the period when Ae. aegypti disappeared from Brisbane, the largest population centre in Queensland, Australia. In particular, we focus on the targeted management of Ae. aegypti by government authorities, that led to local elimination, something rarely observed in large cities. Numerous factors are likely to be responsible including the removal of larval habitat, especially domestic rainwater tanks, in combination with increased mosquito surveillance and regulatory enforcement. This account of historical events as they pertain to the elimination of Ae. aegypti from Brisbane, will inform assessments of the risks posed by recent human responses to climate change and the reintroduction of 300,000 rainwater tanks into the State over the past decade.

Effects of socio-demographic characteristics and household water management on Aedes aegypti production in suburban and rural villages in Laos and Thailand.

BACKGROUND: Dengue fever is a mosquito-borne disease accounting for 50-100 million annual cases globally. Laos and Thailand are countries in south-east Asia where the disease is endemic in both urban and rural areas. Household water storage containers, which are favourable breeding sites for dengue mosquitoes, are common in these areas, due to intermittent or limited access to water supply. This study assessed the effect of household water management and socio-demographic risk factors on Aedes aegypti infestation of water storage containers. METHODS: A cross-sectional survey of 239 households in Laos (124 suburban and 115 rural), and 248 households in Thailand (127 suburban and 121 rural) was conducted. Entomological surveys alongside semi-structured interviews and observations were conducted to obtain information on Ae. aegypti infestation, socio-demographic factors and water management. Zero-inflated negative binomial regression models were used to assess risk factors associated with Ae. aegypti pupal infestation. RESULTS: Household water management rather than socio-demographic factors were more likely to be associated with the infestation of water containers with Ae. aegypti pupae. Factors that was significantly associated with Ae. aegypti infestation were tanks, less frequent cleaning of containers, containers without lids, and containers located outdoors or in toilets/bathrooms. CONCLUSIONS: Associations between Ae. aegypti pupae infestation, household water management, and socio-demographic factors were found, with risk factors for Ae. aegypti infestation being specific to each study setting. Most of the containers did not have lids, larvicides, such as temephos was seldom used, and containers were not cleaned regularly; factors are facilitating dengue vector proliferation. It is recommended that, in Lao villages, health messages should promote proper use and maintenance of tightly fitted lids, and temephos in tanks, which were the most infested containers. Recommendations for Thailand are that small water containers should be cleaned weekly. Furthermore, in addition to health messages on dengue control provided to communities, attention should be paid to larval control for indoor containers in rural villages. Temephos or other immature control measures such as the use of pyriproxyfen, antilarval bacteria, or larvivorous fish should be used where temephos resistance is prevalent. Dengue control is not possible without additional adult mosquito control and community participation.