Mosquito Contact Research Articles

Laboratory evaluation of the contact irritancy of a clothianidin solo formulation vs. clothianidin-deltamethrin mixture formulations for indoor residual spraying against pyrethroid-resistant Anopheles gambiae sensu lato

BackgroundClothianidin-based indoor residual spraying (IRS) formulations have become available for malaria control as either solo formulations of clothianidin or a mixture of clothianidin with the pyrethroid deltamethrin. While both formulations have been successfully used for malaria control, studies investigating the effect of the pyrethroid in IRS mixtures may help improve our understanding for development of future IRS products. It has been speculated that the irritant effect of the pyrethroid in the mixture formulation may result in shorter mosquito contact times with the treated walls potentially leading to a lower impact.MethodsWe compared contact irritancy expressed as the number of mosquito take-offs from cement surfaces treated with an IRS formulation containing clothianidin alone (SumiShield® 50WG) to clothianidin-deltamethrin mixture IRS formulations against pyrethroid-resistant Anopheles gambiae sensu lato under controlled laboratory conditions using a modified version of the World Health Organisation cone bioassay. To control for the pyrethroid, comparison was made with a deltamethrin-only formulation. Both commercial and generic non-commercial mixture formulations of clothianidin and deltamethrin were tested.ResultsThe clothianidin solo formulation did not show significant contact irritancy relative to the untreated control (3.5 take-offs vs. 3.1 take-offs, p = 0.614) while all deltamethrin-containing IRS induced significant irritant effects. The number of take-offs compared to the clothianidin solo formulation (3.5) was significantly higher with the commercial clothianidin-deltamethrin mixture (6.1, p = 0.001), generic clothianidin-deltamethrin mixture (7.0, p < 0.001), and deltamethrin-only (8.2, p < 0.001) formulations. The commercial clothianidin-deltamethrin mixture induced similar contact irritancy as the generic clothianidin-deltamethrin mixture (6.1 take-offs vs. 7.0 take-offs, p = 0.263) and deltamethrin-only IRS (6.1 take-offs vs. 8.2, p = 0.071), showing that the irritant effect in the mixture was attributable to its deltamethrin component.ConclusionsThis study provides evidence that the enhanced contact irritancy of the pyrethroid in clothianidin-deltamethrin IRS mixtures can shorten mosquito contact times with treated walls compared to the clothianidin solo formulation. Further trials are needed to directly compare the efficacy of these formulation types under field conditions and establish the impact of this enhanced contact irritancy on the performance of IRS mixture formulations containing pyrethroids.Graphical

Tribal gaps in Malaria in relation to KAP in East Godavari District, Andhra Pradesh

ABSTRACT Objectives: To assess the level of GAPS in knowledge, attitudes and practices among tribal people regarding malaria disease. To assess the interassociation among knowledge, attitude and practices of scores. Materials and Methods: A cross-sectional study was performed in tribal areas of East Godavari District for a period of one year during 2013. Sample size was calculated as 1136. Multistage Random sampling method was used to identify the 4 PHC’s in 4 directions of tribal areas and sample was equally distributed. In that study subjects were selected by using a simple Random method. Data were collected by using a pre-tested, semi-structured questionnaire and results were displayed. Setting: Tribal area of east Godavari district, Andhra Pradesh State, India Participants: Study subjects were selected by simple random method Results: Knowledge–practice gap for source of mosquito breeding 5.99%, for the prevention of mosquito breeding sources and for the implementation of minor engineering measures it is 10.51%. For bush cutting, the knowledge practice gap is -20.07%. For potted plants, the knowledge practice gap is -8.45%. For broken pots, it is 68.93%. IRS is performed outside the house not inside the house. The KAP-GAP for screening is nil. Covering oneself with a blanket to prevent man–mosquito contact is 6.96%. Conclusions: In our study, we found Know-do gap or KAP-GAP in all aspects of prevention of mosquito breeding places and personal protective measures. Regarding the interassociation among knowledge, attitudes and practices, they were associated with each other with significant difference.

Delftia tsuruhatensis TC1 symbiont suppresses malaria transmission by anopheline mosquitoes.

Malaria control demands the development of a wide range of complementary strategies. We describe the properties of a naturally occurring, non-genetically modified symbiotic bacterium, Delftia tsuruhatensis TC1, which was isolated from mosquitoes incapable of sustaining the development of Plasmodium falciparum parasites. D. tsuruhatensis TC1 inhibits early stages of Plasmodium development and subsequent transmission by the Anopheles mosquito through secretion of a small-molecule inhibitor. We have identified this inhibitor to be the hydrophobic molecule harmane. We also found that, on mosquito contact, harmane penetrates the cuticle, inhibiting Plasmodium development. D. tsuruhatensis TC1 stably populates the mosquito gut, does not impose a fitness cost on the mosquito, and inhibits Plasmodium development for the mosquito's life. Contained field studies in Burkina Faso and modeling showed that D. tsuruhatensis TC1 has the potential to complement mosquito-targeted malaria transmission control.

The Bio-efficacy of Inesfly vesta 50 (Transfluthrin 0.5% w/w) insecticidal paint: An alternative vector control intervention against Anoheples gambiae mosquitoes under laboratory condition, Keffi, Nigeria

Malaria remains a major public health concern. Particularly in Nigeria where more than 80% of the cases are reported and locally among natives in Nigeria. There are serious indication of insecticide resistance in Nigeria. Under PMI/Vectorlink laboratory condition, cement plaster surface and wooden board were brushed with a primer within 24-48hours before the paint application. The inesfly vesta 50 (transfluthrin 0.5% w/w) insecticide paint was applied at the dosage of 8m2/L for cement and wooden board drying at room temperature for 5 days. The plastic cones were fixed on the treated walls and wooden board at 0.5m, 1.0m, and 1.5m parameters height, after which 10 non-blood fed females mosquito were gently introduced into the cone chamber for 30- 60 minutes observation. The holding paper cups were kept under favourable temperature of 27oc and humidity at 70%. In a dose trial finding, the data obtained were analyzed in IBM SPSS version 23.0 using ANOVA and the results presented as mean ± standard deviations of triplicate observations showed 100% yield (100.0±0.00*) mortality of malaria vector of novel trial with 0.5% w/w transfluthrin painted substrates in 24hours post exposure to 6months post application, except that, at l.5m in the month of July, 98% knockdown/mortality was recorded which follow same sequence of method and procedure in the application on the substrate absorbency, though, results showed high level of susceptibility from February to July (100% mortality rate). Results from wall cone and wooden board bio-assay residuality was alarming, with very high kill rates observed after 24hours post exposure. From the treated bio-assay of inesfly vesta 50 (Transfluthrin 0.5% w/w) by possible means showed that, this formulation is effective on malaria vector and possibly other insects. This suggests that, the transfluthrin 0.5% w/w can be tried alongside other known application with organophosphate, pyrethroids and the carbamate group, and can reduce human mosquito contact and impact on the perennial malaria transmission.

Narrative Review: Quintuple Helixs Model for Malaria Elimination in Indonesia

Malaria continues to impact the health and economies of people around the world. Further steps need to be taken in accordance with the Global Technical Strategy for malaria to prevent malaria transmission. Quintuple helix model is an integrated effort that involves cross-sector in controlling malaria cases in an area. The implementation of the quintuple helix model is expected to be used as consideration and input for policy makers in an effort to achieve malaria elimination in Indonesia by 2030. The purpose of this study is to eliminate malaria in Indonesia with the quintuple helix model. This study uses a systematic review narrative method that is used to identify study topics selectively on interesting and recent issues. Malaria control in Indonesia is carried out using the national resilience approach. The results obtained from the academic aspect for malaria control must be met, both in terms of educational background qualifications, from the industrial aspect of the economic system included in the quintuple helix model, from the government aspect the control program must be compiled under the Ministry of Health, from the media aspect where the media is one of the an important index in the management of malaria in an area, and from an environmental aspect that aims to prevent, limit vector breeding and reduce mosquito contact with humans. The quintuple helix model is expected to be an innovation in malaria control in Indonesia. By involving academia and social community, industry, government, environmental engineering and the media. It is hoped that each sector can provide roles that are in accordance with their duties and functions

Analisis Faktor Risiko Malaria di Asia Tenggara

Malaria is a disease caused by the parasites of the genus Plasmodium, which are transmitted by the bite of the female Anopheles mosquito. All tropical countries, including Southeast Asia, reported malaria cases. Several factors related to human behavior and the environment in which people live cause the incidence of malaria. The objective of this study was to analyze the risk factors for malaria in Southeast Asia and determine which risk variables had the greatest impact on the prevalence of malaria. This study is a review of the literature with a narrative review model using English and Indonesian journals from 2017 to 2021. The journals were obtained through the health journal provider databases Pubmed, Google Scholar, ScienceDirect, Researchgate, and Academic.edu. Malaria risk factors in Southeast Asia are influenced by behavioral and environmental factors. Behavioral factors include not use of mosquito nets, being active at night, male gender, and risky work. Environmental factors include rural areas, open-access dwellings, housing near cattle pens, and proximity to mosquito breeding sites. Changes in human behavior to avoid mosquito contact and environmental control are required to reduce the incidence of malaria.

A closer look at the WHO cone bioassay: video analysis of the hidden effects of a human host on mosquito behaviour and insecticide contact

BackgroundThe WHO cone test is one of three tests currently used to evaluate the efficacy of insecticide-treated bed nets (ITNs). It generates two test outputs, knockdown and 24-h mortality, both indicative of immediate toxicity but that reveal little about the nature of mosquito and ITN interaction or how results translate to real-world settings.MethodsA human arm held 5 mm behind the net surface acted as a host attractant during cone tests and a smartphone was used to capture mosquito behaviour in the cone. Post-exposure blood feeding and survival for nine days were recorded; ingested blood meal size was determined by measuring excreted haematin. Four strains of Anopheles gambiae (insecticide susceptible: Kisumu and N’gousso; insecticide resistant: Banfora and VK7) were tested with and without the host attractant using untreated, Permanet 2.0 and Olyset nets. Video recordings were scan sampled every five seconds to record mosquito positions on either the net, in flight or in contact with the cone. Generalized estimating equations were used to analyse all data except survival within nine days which was analysed using Weighted Cox Regression.ResultsNet contact was the most frequently recorded behaviour in all Anopheles spp. strains on all nets. Adding the human host as attractant triggered excitatory behaviours: in all strains, the magnitude of net contact was significantly decreased compared to tests without a host. ITN exposure altered the observed behaviour of the two susceptible strains, which exhibited a decreased response to the host during ITN tests. The resistant strains did not alter their behaviour during ITN tests. Significantly less net contact was observed during Olyset Net tests compared to Permanet 2.0. The host presence affected survival after exposure: Banfora and VK7 mosquitoes exposed to Permanet 2.0 with a host lived longer compared to tests performed without a host. However, mosquitoes that blood-fed and survived long enough to digest the blood meal did not exhibit significantly reduced longevity regardless of the presence of the host attractant.ConclusionsSimple modifications to the WHO cone test and extension of post-test monitoring beyond the current 24 h enable detailed behavioural characterizations of individual ITNs to be compiled. The effects observed from testing with a host and including blood feeding suggest that more representative estimates of true of ITN efficacy are gained with these modifications than when using the current testing protocol.

Human-Mosquito Contact: A Missing Link in Our Understanding of Mosquito-Borne Disease Transmission Dynamics.

Despite the critical role that contact between hosts and vectors, through vector bites, plays in driving vector-borne disease (VBD) transmission, transmission risk is primarily studied through the lens of vector density and overlooks host–vector contact dynamics. This review article synthesizes current knowledge of host–vector contact with an emphasis on mosquito bites. It provides a framework including biological and mathematical definitions of host–mosquito contact rate, blood-feeding rate, and per capita biting rates. We describe how contact rates vary and how this variation is influenced by mosquito and vertebrate factors. Our framework challenges a classic assumption that mosquitoes bite at a fixed rate determined by the duration of their gonotrophic cycle. We explore alternative ecological assumptions based on the functional response, blood index, forage ratio, and ideal free distribution within a mechanistic host–vector contact model. We highlight that host–vector contact is a critical parameter that integrates many factors driving disease transmission. A renewed focus on contact dynamics between hosts and vectors will contribute new insights into the mechanisms behind VBD spread and emergence that are sorely lacking. Given the framework for including contact rates as an explicit component of mathematical models of VBD, as well as different methods to study contact rates empirically to move the field forward, researchers should explicitly test contact rate models with empirical studies. Such integrative studies promise to enhance understanding of extrinsic and intrinsic factors affecting host–vector contact rates and thus are critical to understand both the mechanisms driving VBD emergence and guiding their prevention and control.

Mosquito repellence induced by tarsal contact with hydrophobic liquids

Mosquito legs have a unique highly water-repellent surface structure. While being beneficial to mosquitoes, the water-repellence of the tarsi enhances the wettability of hydrophobic substances such as oils. This high wettability induces strong attraction forces on a mosquito’s legs (up to 87% of the mosquito’s weight) towards the oil. We studied the landing behaviour of mosquitoes on oil-coated surfaces and observed that the mosquito contact time was reduced compared to that on hydrophilic-liquid-coated surfaces, suggesting that the oil coating induces an escape response. The observed escape behaviour occurred consistently with several hydrophobic liquids, including silicone oil, which is used globally in personal care products. As the repellent effect is similar to multiple hydrophobic substances, it is likely to be mechanically stimulated owing to the physical properties of the hydrophobic liquids and not due to chemical interactions. On human skin, the contact time was sufficiently short to prevent mosquitoes from starting to blood-feed. The secretion of Hippopotamus amphibius, which has physical properties similar to those of low-viscosity silicone oil, also triggered an escape response, suggesting that it acts as a natural mosquito repellent. Our results are beneficial to develop new, safe, and effective mosquito-repellent technologies.

Risk Factors of Acute Respiratory Infections in Children under Five Years Attending the Fishtail Hospital, Pokhara, Nepal

Introduction: Acute Respiratory Infection (ARI) is one of the leading causes of morbidity and mortality in under five-year children. Risk factors include age, sex, socio‐economic status, indoor air pollution, passive smoking, lack of basic health services, and lack of awareness. In this study, we aimed to determine the associated risk factors of ARI in children under five-years of age.&#x0D; Methods: We carried out a hospital-based descriptive cross-sectional study in the peak period of of November 2017 to February 2018. The study was conducted in Fishtail Hospital and Research Center (FHRC), Pokhara, Nepal. Non probability, purposive sampling technique was used and a structural interview was taken for data collection. The tool comprised of two main parts. Part I- questions related to socio-demographic variables of mother and baby. Part II- questions related to risk factors of ARI. The collected data was analyzed using Statistical Package for Social Science (SPSS) software, version 16. The Chi Square statistic is used for testing relationships between categorical variables.&#x0D; Results: In total of 302 children visited to FHRC with the symptoms of ARI, only 188 (63%) were diagnosed as ARI. The most common symptoms were fever (42.2%), cough (35.7%), running nose (34.1%), difficulty in breathing (28.5%) and chest in drawing (11.6%). The age of children with ARI ranged from one to sixty month with the mean age of 21.46 ±13.52. Among 188 children, 51% were males whereas 49%were females. There were no statistically differences of children weight at birth among ARI. Our results revealed environmental and social factors associated with ARI.&#x0D; Conclusions: The risk factors significantly associated with ARI were malnutrition, exposure to wood smoke and mosquito coil and contact with person having ARI. Reducing these conditions may reduce the morbidity and mortality associated with ARI in children.

Influence of Demography, Land Use, and Urban Form on West Nile Virus Risk and Human West Nile Virus Incidence in Ottawa, Canada.

Human infection by West Nile virus (WNV; family Flaviviridae), in some cases, develops into a deadly neuroinvasive disease. WNV risk is thought to be influenced by factors affecting the density of species that promote replication and transmission of the virus, namely peridomestic bird and mosquito species. Factors influencing contact between peridomestic bird and mosquito species and contact between infected mosquitoes and vulnerable human populations may also be important in determining WNV risk in an area. Several urban form and demographic factors, such as population density and the proportion of aged housing units, have been linked with increased WNV risk. Other factors, such as proportion of old-growth forest and wetlands, have been linked to decreased WNV risk. In this study, we aimed to test the effect of several demographic, land use, and urban form variables on WNV risk within neighborhoods of the city of Ottawa, Canada, based on the spatiotemporal clustering of infected mosquitoes and human WNV cases. We found a large positive effect of population density and proportion of aged housing units on WNV risk, using both entomological and epidemiological data. Interestingly, we found a large negative effect of proportion of natural areas in our epidemiological analysis, but not in our entomological analysis. Although our epidemiological data set was relatively small, these results suggest entomological surveillance results should be interpreted alongside other factors when investigating risk to humans. Our study is also one of the few to suggest an effect of demography, land use, and urban form on WNV risk in a Canadian urban center, using both entomological and epidemiological data.

A study on knowledge attitudes and practices on mal aria among tribal communities of East Godavari district, Andhra Pradesh

Background: Malaria is one of the world’s important parasitic diseases ever known to mankind. The global toll of malaria in 2010 there were an estimated 216 million cases of malaria worldwide. India is predominantly characterized by unstable malaria transmission. In Andhra Pradesh among five endemic districts East Godavari is one. We made an attempt to report knowledge and practices on malaria regarding its causation, transmission, symptoms, diagnosis, treatment and prevention.Methods: Using a systematic random method a total of 1136 participants were interviewed in four tribal P.H.C areas of East Godavari district. P.H.C‘s was identified by using a multistage random method. A semi-structured questionnaire which consists questions on malaria causation, transmission, symptoms, diagnosis, treatment and prevention were used as a tool to interview them. Data were entered into excel sheets and analysed by giving scorings and its categorization as good, average and poor.Results: Knowledge among study participants on Cause, diagnosis and treatment of malaria 41.67%, man mosquito contact among study participants- 22.53%. Attitude among study participants regarding cause, diagnosis and treatment of malaria 56.22%, mosquito breeding places 45.77%, prevention of man mosquito contact 46.71%. Practices among study participants on preventive practices on cause, diagnosis and treatment 49.56%, prevention of mosquito breeding places and man mosquito contact- 42.54%.Conclusions: In our study we found more knowledge regarding cause, diagnosis and treatment of malaria. Attitudes for prevention of mosquito breeding places are quite high. Less than half of the preventive practices were reported.

Papaya Leaf (Carica papaya L.) Active Fraction Effective as Bioinsectiside Against Anopheles species (Diptera: Culicidae) Larva Invitro Study

ABSTRACT&#x0D; &#x0D; Malaria is one of the spread-disease that become a global public health problem included Indonesia. One of the controlling approach of vector-borne disease is by avoiding direct contact of human and mosquitoes. Natural insecticide is an alternative method that can be used. Carica papaya L. is one of the natural insecticide because contains of alkaloid, flavonoid and saponin. This research was aimed to determine the activity of active fraction. was a quasi-experiment research with post test only group design. This research was conducted in April – June 2017. Extraction and fractination was performed in laboratory of MIPA Biologi of Sriwijaya University. The experiment was performed in laboratory of Entomologi Baturaja. The sample of the research was Anopheles sp. larva instar III and IV. Larvacide test used 6 different concentrations which was 0,125%, 0,25%, 0,5%, 1,0% and 2,0% with aquadest as a control. Anova test and post hoc analysis with SPSS 22 software. The result of efficacy test to Anopheles sp. larva showed that N-hexan was the fraction with highest larvacide ability that kill 95% larva at 2% concentration level. Thin layer chromatography test showed a compound of Terpenoid. Activity test of active fraction N-heksan of papaya leaf with the highest mortality rate 92,5% and the lowest 46,25%. LC50 fraction N-heksan of papaya leaf was high toxicity at 24 hours of observation. Anova test showed there was significant influence and difference of various concentration of active fraction of papaya leaf to the mortality of Anopheles sp. larva with p value &lt; α (0,00&lt;0,05).&#x0D; &#x0D; Key words : Anopheles sp. larva, N-hexan fraction of papaya leaf, larvacide&#x0D;

Meta-Analysis of Aedes aegypti Expression Datasets: Comparing Virus Infection and Blood-Fed Transcriptomes to Identify Markers of Virus Presence.

The mosquito Aedes aegypti (L.) is vector of several arboviruses including dengue, yellow fever, chikungunya, and more recently zika. Previous transcriptomic studies have been performed to elucidate altered pathways in response to viral infection. However, the intrinsic coupling between alimentation and infection were unappreciated in these studies. Feeding is required for the initial mosquito contact with the virus and these events are highly dependent. Addressing this relationship, we reinterrogated datasets of virus-infected mosquitoes with two different diet schemes (fed and unfed mosquitoes), evaluating the metabolic cross-talk during both processes. We constructed coexpression networks with the differentially expressed genes of these comparison: virus-infected versus blood-fed mosquitoes and virus-infected versus unfed mosquitoes. Our analysis identified one module with 110 genes that correlated with infection status (representing ~0.7% of the A. aegypti genome). Furthermore, we performed a machine-learning approach and summarized the infection status using only four genes (AAEL012128, AAEL014210, AAEL002477, and AAEL005350). While three of the four genes were annotated as hypothetical proteins, AAEL012128 gene is a membrane amino acid transporter correlated with viral envelope binding. This gene alone is able to discriminate all infected samples and thus should have a key role to discriminate viral infection in the A. aegypti mosquito. Moreover, validation using external datasets found this gene as differentially expressed in four transcriptomic experiments. Therefore, these genes may serve as a proxy of viral infection in the mosquito and the others 106 identified genes provides a framework to future studies.

Perception and practices pertaining to prevention and control of dengue fever among rural population in Mysore district

Background: Dengue is the most prevalent arboviral disease in human beings, with 3.6 billion people living in areas with risk of disease transmission. Many dengue prevalence studies have been conducted in urban areas but it is important to remember the often-forgotten rural population who are also affected. The objective of the study was to assess the perceptions and practices related to dengue among residents of rural community.Methods: A community based cross sectional study was conducted for a period of two months, at Suttur village of Mysore district. Total of 200 individuals were interviewed by doing house to house survey to obtain details of socio-demographic characteristics, perceptions regarding dengue and practices of preventive measures for mosquito breeding and man mosquito contact were obtained using a pre tested questionnaire. Results: In the present study 42 (21%) members had ever heard of the disease called dengue and 18 (42.85%) of them knew that dengue fever spreads by mosquito bite and 12 (28.57%) people said it spreads by drinking dirty water, none of them knew which species of mosquitoes spread dengue fever. Many of them perceive that mosquito spreading Dengue breads in dirty water and garbage. Majority of the people used bed nets, mosquito coil and fans as methods of personal protection and 97% they followed weekly cleaning of water containers to eliminate mosquito breeding. Conclusions: the study shows, the knowledge regarding cause, modes of spread of dengue and vector characteristics were poor but the practices towards mosquito control and eliminating the breeding places of mosquito were adequate.

Improving the built environment in urban areas to control Aedes aegypti-borne diseases.

The vector Aedes aegypti is now present in nearly every tropical and sub-tropical region in the world and poses a threat to health globally. The mosquito can transmit several viruses that cause diseases, such as dengue fever, chikungunya, yellow fever and Zika virus infection. Recent outbreaks of Ae. aegypti-borne diseases have shown that urban areas are particularly vulnerable because the built environment provides ideal conditions for mosquito proliferation and contact with humans. Unless the global public health community takes a coordinated, pre-emptive approach to controlling the Ae. aegypti population, these outbreaks will become more common and widespread as urban populations expand and movement of people and their goods increase. Improving the built environment would contribute to a long-term solution to reducing the threat of Ae. aegypti-bome diseases. Our ability to deal with Ae. Aegypti-borne viral epidemics is limited. Apart from supportive care, specific treatments for vector-borne viral diseases are lacking. No commercial vaccines for Zika or chikungunya are available, the only licensed dengue vaccine is partially protective (1) and globally the yellow fever vaccine is in short supply. (2) Although current vector control programmes are often poorly resourced and under-used, (3) historically, vector control was the main method for controlling mosquito-borne diseases. By using container inspections, oiling of breeding sites and later perifocal spraying of DDT (dichlorodiphenyltrichloroethane) in water containers and on nearby walls, Ae. aegypti, yellow fever and dengue fever were successfully eliminated from much of South America in the 1960s. (4) In the 1970s and 1980s in Singapore and in the 1980s and 1990s in Cuba, controlling adult and larval Ae. aegypti reduced dengue transmission. In the future, new methods of vector control, such as novel delivery systems for insecticides with new modes of action and release of Wolbachia-infected or genetically-modified mosquitoes, may contribute to the control or elimination of mosquito-borne diseases. (5) Affected towns and cities, however, already have several options to reduce Ae. aegyptibome diseases and these options should be built into future planning strategies. Current Ae. aegypti control focuses on reducing densities of immature and adult mosquitoes with larvicides or adult insecticides. While these interventions can be effective, continued reliance on these single-intervention control programmes is resource-intensive and threatened by insecticide resistance. The World Health Organization (3,6) and other major international organizations7 have recommended an intersectoral approach to achieve more effective and sustainable vector control. Governments, however, have often overlooked such approaches when designing vector control programmes. An underutilized aspect of integrated vector management is improving the urban built environment to reduce Ae. aegypti populations and their contact with humans. (8) The built environment in many urban areas provides abundant habitats for the immature stages of Ae. aegypti, and high human population densities create the potential for large outbreaks of Aedes-borne diseases. More than half of the world's population currently lives in urban areas and by 2050 it is estimated that 70% of the population will live in cities. (9) This urban expansion will increase the frequency and intensity of Aedes-borne outbreaks. However, developing urban areas that minimize human contact with mosquitoes could enable sustainable and cost-effective prevention of mosquito-borne diseases. Several aspects of urban planning can be targeted to reduce human contact with Ae. aegypti. Reducing the availability of small plastic containers around homes and improving solid waste management will remove habitats for Ae. aegypti larvae development. Provision of constant piped water will reduce the need to store water in containers in and around homes, since water-filled containers are known to be favoured habitats for Ae. …

Distribution and abundance of key vectors of Rift Valley fever and other arboviruses in two ecologically distinct counties in Kenya.

BackgroundRift Valley fever (RVF) is a mosquito-borne viral zoonosis of ruminants and humans that causes outbreaks in Africa and the Arabian Peninsula with significant public health and economic consequences. Humans become infected through mosquito bites and contact with infected livestock. The virus is maintained between outbreaks through vertically infected eggs of the primary vectors of Aedes species which emerge following rains with extensive flooding. Infected female mosquitoes initiate transmission among nearby animals, which amplifies virus, thereby infecting more mosquitoes and moving the virus beyond the initial point of emergence. With each successive outbreak, RVF has been found to expand its geographic distribution to new areas, possibly driven by available vectors. The aim of the present study was to determine if RVF virus (RVFV) transmission risk in two different ecological zones in Kenya could be assessed by looking at the species composition, abundance and distribution of key primary and secondary vector species and the level of virus activity.MethodologyMosquitoes were trapped during short and long rainy seasons in 2014 and 2015 using CO2 baited CDC light traps in two counties which differ in RVF epidemic risk levels(high risk Tana-River and low risk Isiolo),cryo-preserved in liquid nitrogen, transported to the laboratory, and identified to species. Mosquito pools were analyzed for virus infection using cell culture screening and molecular analysis.FindingsOver 69,000 mosquitoes were sampled and identified as 40 different species belonging to 6 genera (Aedes, Anopheles, Mansonia, Culex, Aedeomyia, Coquillettidia). The presence and abundance of Aedes mcintoshi and Aedes ochraceus, the primary mosquito vectors associated with RVFV transmission in outbreaks, varied significantly between Tana-River and Isiolo. Ae. mcintoshi was abundant in Tana-River and Isiolo but notably, Aedes ochraceus found in relatively high numbers in Tana-River (n = 1,290), was totally absent in all Isiolo sites. Fourteen virus isolates including Sindbis, Bunyamwera, and West Nile fever viruses were isolated mostly from Ae. mcintoshi sampled in Tana-River. RVFV was not detected in any of the mosquitoes.ConclusionThis study presents the geographic distribution and abundance of arbovirus vectors in two Kenyan counties, which may assist with risk assessment for mosquito borne diseases.

Optimal control and cost-effectiveness analysis of a three age-structured transmission dynamics of chikungunya virus

Chikungunya is an RNA viral disease, transmitted to humans by infected Aedes aegypti or Aedes albopictus mosquitoes. In this paper, an age-structured deterministic model for the transmission dynamics of Chikungunya virus is presented. The model is locally and globally asymptotically stable when the reproduction number is less than unity. A global sensitivity analysis using the reproduction number indicates that the mosquito biting rate, the transmission probability per contact of mosquitoes and of humans, mosquito recruitment rate and the death rate of the mosquitoes are the parameters with the most influence on Chikungunya transmission dynamics. Optimal control theory was then applied, using the results from the sensitivity analysis, to minimize the number infected humans, with time dependent control variables (impacting mosquito biting rate, transmission probability, death rate and recovery rates in humans). The numerical simulations indicate that Chikungunya can be reduced by the application of these controls. The benefits associated with these health interventions are evaluated using cost-effectiveness analysis and these shows that using mono-control strategy involving treatment of infected individuals is the most cost-effective strategy of this category. With pairs of control, the pairs involving treatment of infected individuals and mosquitoes adulticiding, is the most cost-effective strategy of this category and is more cost-effective than using the triple control strategy involving personal protection, treatment of infected humans and mosquitoes adulticiding.

Zika virus and neurology: proving cause and effect.

‘Zika fever’ was first reported in Uganda and Tanzania in 1952. Caused by the Zika flavivirus it consisted of a mild and self-limiting illness of rash, low-grade fever, conjunctivitis, headache and myalgia. Two strains of Zika virus were subsequently identified (African and Asian) with transmission via mosquito or sexual contact. Since 2007 there have been several epidemics of the Asian strain including in French Polynesia (2013–2014; 20,000 cases) and Brazil (2015–2016; 30,000 cases), and these outbreaks have been associated with increased incidence of Guillain–Barre syndrome (GBS) in adults and microcephaly in infants. Proving a causative link between an infectious agent and subsequent neurological damage is not straightforward. This month’s journal club examines three papers that attempt to provide evidence connecting Zika virus to neurological sequelae. The first is a case–control study of GBS during the Zika virus epidemic in French Polynesia. The second is a prospective cohort study reporting foetal growth defects in pregnant women in Brazil, some of whom had been infected with Zika virus. The third is a cellular paper looking at neural expression of AXL, a receptor that could mediate Zika virus entry into cells.

Synergistic mosquito-repellent activity of Curcuma longa, Pogostemon heyneanus and Zanthoxylum limonella essential oils

Mosquito repellents play an important role in preventing man-mosquito contact. In the present study, we evaluated the synergistic mosquito-repellent activity of Curcuma longa, Pogostemon heyneanus and Zanthoxylum limonella essential oils. The mosquito repellent efficacies of three essential oils were evaluated separately and in combination under laboratory and field conditions. N,N-Diethylphenylacetamide (DEPA) and dimethylphthalate (DMP) were used for comparison of the protection time of the mixture of essential oils. At an optimum concentration of 20%, the essential oils of C. longa, Z. limonella and P. heyneanus provided complete protection times (CPTs) of 96.2, 91.4 and 123.4 min, respectively, against Aedes albopictus mosquitoes in the laboratory. The 1:1:2 mixture of the essential oils provided 329.4 and 391.0 min of CPT in the laboratory and field trials, respectively. The percent increases in CPTs for the essential oil mixture were 30 for DMP and 55 for N,N-diethylphenylacetamide (DEPA). The synergistic repellent activity of the essential oils used in the present study might be useful for developing safer alternatives to synthetic repellents for personal protection against mosquitoes.