Species abundance, composition, and nocturnal activity of female Anopheles (Diptera: Culicidae) in malaria-endemic villages of Papua New Guinea: assessment with barrier screen sampling.

BACKGROUND: Community composition of Anopheles mosquitoes, and their host-seeking and peridomestic behaviour, are important factors affecting malaria transmission. In this study, barrier screen sampling was used to investigate species composition, abundance, and nocturnal activity of Anopheles populations in villages of Papua New Guinea. METHODS: Mosquitoes were sampled from 6 pm to 6 am in five villages from 2012 to 2016. The barrier screens were positioned between the village houses and the perimeter of villages where cultivated and wild vegetation ("the bush") grew thickly. Female Anopheles that rested on either village or bush side of the barrier screens, as they commuted into and out of the villages, were captured. Similarity in species composition among villages was assessed. Mosquitoes captured on village and bush sides of the barrier screens were sorted by feeding status and by hour of collection, and their numbers were compared using negative binomial generalized linear models. RESULTS: Females of seven Anopheles species were present in the sample. Species richness ranged from four to six species per village, but relative abundance was highly uneven within and between villages, and community composition was similar for two pairs of villages and highly dissimilar in a fifth. For most Anopheles populations, more unfed than blood-fed mosquitoes were collected from the barrier screens. More blood-fed mosquitoes were found on the side of the barrier screens facing the village and relatively more unfed ones on the bush side, suggesting commuting behaviour of unfed host-seeking females into the villages from nearby bush and commuting of blood-fed females away from villages towards the bush. For most populations, the majority of host-seeking mosquitoes arrived in the village before midnight when people were active and unprotected from the mosquitoes by bed nets. CONCLUSION: The uneven distribution of Anopheles species among villages, with each site dominated by different species, even among nearby villages, emphasizes the importance of vector heterogeneity in local malaria transmission and control. Yet, for most species, nocturnal activity patterns of village entry and host seeking predominantly occurred before midnight indicating common behaviours across species and populations relative to human risk of exposure to Anopheles bites.

ResistanceSim: development and acceptability study of a serious game to improve understanding of insecticide resistance management in vector control programmes.

The use of insecticides is the cornerstone of effective malaria vector control. However, the last two decades has seen the ubiquitous use of insecticides, predominantly pyrethroids, causing widespread insecticide resistance and compromising the effectiveness of vector control. Considerable efforts to develop new active ingredients and interventions are underway. However, it is essential to deploy strategies to mitigate the impact of insecticide resistance now, both to maintain the efficacy of currently available tools as well as to ensure the sustainability of new tools as they come to market. Although the World Health Organization disseminated best practice guidelines for insecticide resistance management (IRM), Rollback Malaria's Vector Control Working Group identified the lack of practical knowledge of IRM as the primary gap in the translation of evidence into policy. ResistanceSim is a capacity strengthening tool designed to address this gap. The development process involved frequent stakeholder consultation, including two separate workshops. These workshops defined the learning objectives, target audience, and the role of mathematical models in the game. Software development phases were interspersed with frequent user testing, resulting in an iterative design process. User feedback was evaluated via questionnaires with Likert-scale and open-ended questions. The game was regularly evaluated by subject-area experts through meetings of an external advisory panel. Through these processes, a series of learning domains were identified and a set of specific learning objectives for each domain were defined to be communicated to vector control programme personnel. A simple "game model" was proposed that produces realistic outputs based on player strategy and also runs in real-time. Early testing sessions revealed numerous usability issues that prevented adequate player engagement. After extensive revisions, later testing sessions indicated that the tool would be a valuable addition to IRM training.

Mosquito Behavior Change After Distribution of Bednets Results in Decreased Protection Against Malaria Exposure.

Background: Behavioral resilience in mosquitoes poses a significant challenge to mosquito control. Although behavior changes in anopheline vectors have been reported over the last decade, there are no empirical data to suggest they compromise the efficacy of vector control in reducing malaria transmission. Methods: In this study, we quantified human exposure to both bites and infective bites of a major malaria vector in Papua New Guinea over the course of 4 years surrounding nationwide bednet distribution. We also quantified malaria infection prevalence in the human population during the same time period. Results: We observed a shift in mosquito biting to earlier hours of the evening, before individuals are indoors and protected by bednets, followed by a return to preintervention biting rates. As a result, net users and non-net users experienced higher levels of transmission than before the intervention. The personal protection provided by a bednet decreased over the study period and was lowest in the adult population, who may be an important reservoir for transmission. Malaria prevalence decreased in only 1 of 3 study villages after the distribution. Discussion: This study highlights the necessity of validating and deploying vector control measures targeting outdoor exposure to control and eliminate malaria.

An Operational Framework for Insecticide Resistance Management Planning.

Arthropod vectors transmit organisms that cause many emerging and reemerging diseases, and their control is reliant mainly on the use of chemical insecticides. Only a few classes of insecticides are available for public health use, and the increased spread of insecticide resistance is a major threat to sustainable disease control. The primary strategy for mitigating the detrimental effects of insecticide resistance is the development of an insecticide resistance management plan. However, few examples exist to show how to implement such plans programmatically. We describe the formulation and implementation of a resistance management plan for mosquito vectors of human disease in Zambia. We also discuss challenges, steps taken to address the challenges, and directions for the future.

Malaria transmission dynamics surrounding the first nationwide long-lasting insecticidal net distribution in Papua New Guinea.

BACKGROUND: The major malaria vectors of Papua New Guinea exhibit heterogeneities in distribution, biting behaviour and malaria infection levels. Long-lasting, insecticide-treated nets (LLINs), distributed as part of the National Malaria Control Programme, are the primary intervention targeting malaria transmission. This study evaluated the impact of LLINs on anopheline density, species composition, feeding behaviour, and malaria transmission. METHODS: Mosquitoes were collected by human landing catch in 11 villages from East Sepik Province and Madang Province. Mosquitoes were collected for 3 years (1 year before distribution and 2 years after), and assayed to determine mosquito species and Plasmodium spp. infection prevalence. The influence of weather conditions and the presence of people and animals on biting density was determined. Determinants of biting density and sporozoite prevalence were analysed by generalized estimating equations (GEE). RESULTS: Mosquito biting rates and entomological inoculation rates decreased significantly after the distribution. Plasmodium falciparum and P. vivax sporozoite prevalence decreased in year 2, but increased in year 3, suggesting the likelihood of resurgence in transmission if low biting rates are not maintained. An earlier shift in the median biting time of Anopheles punctulatus and An. farauti s.s. was observed. However, this was not accompanied by an increase in the proportion of infective bites occurring before 2200 hours. A change in species composition was observed, which resulted in dominance of An. punctulatus in Dreikikir region, but a decrease in An. punctulatus in the Madang region. When controlling for village and study year, An. farauti s.s., An. koliensis and An. punctulatus were equally likely to carry P. vivax sporozoites. However, An. punctulatus was significantly more likely than An. farauti s.s. (OR 0.14; p = 0.007) or An. koliensis (OR 0.27; p < 0.001) to carry P. falciparum sporozoites. CONCLUSIONS: LLINs had a significant impact on malaria transmission, despite exophagic and crepuscular feeding behaviours of dominant vectors. Changes in species composition and feeding behaviour were observed, but their epidemiological significance will depend on their durability over time.

Efficacy, Safety, and Pharmacokinetics of Coadministered Diethylcarbamazine, Albendazole, and Ivermectin for Treatment of Bancroftian Filariasis.

BACKGROUND: Available treatments for lymphatic filariasis (LF) are limited in their longterm clearance of microfilaria from the blood. The safety and efficacy of a single-dose triple-drug therapy of the antifilarial drugs diethylcarbamazine (DEC), ivermectin (IVM), and albendazole (ALB) for LF are unknown. METHODS: We performed a pilot study to test the efficacy, safety, and pharmacokinetics of single-dose DEC, IVM, and ALB in Wuchereria bancrofti-infected Papua New Guineans. Adults were randomized into 2 treatment arms, DEC 6 mg/kg + ALB 400 mg (N = 12) or DEC 6 mg/kg + ALB 400 mg + IVM 200 µg/kg (N = 12), and monitored for microfilaria, parasite antigenemia, adverse events (AEs), and serum drug levels. RESULTS: Triple-drug therapy induced >2-log reductions in microfilaria levels at 36 and 168 hours after treatment compared with approximately 1-log reduction with 2 drugs. All 12 individuals who received 3 drugs were microfilaria negative 1 year after treatment, whereas 11 of 12 individuals in the 2-drug regimen were microfilaria positive. In 6 participants followed 2 years after treatment, those who received 3 drugs remained microfilaria negative. AEs, particularly fever, myalgias, pruritus, and proteinuria/hematuria, occurred in 83% vs 50% of those receiving triple-drug compared to 2-drug treatment respectively (P = .021); all resolved within 7 days after treatment. No serious AEs were observed in either group. There was no significant effect of IVM on DEC or ALB drug levels. CONCLUSIONS: Triple-drug therapy is safe and more effective than DEC + ALB for Bancroftian filariasis and has the potential to accelerate elimination of lymphatic filariasis. CLINICAL TRIALS REGISTRATION: NCT01975441.

Fit for purpose: do we have the right tools to sustain NTD elimination?

Priorities for NTD control programmes will shift over the next 10-20 years as the elimination phase reaches the 'end game' for some NTDs, and the recognition that the control of other NTDs is much more problematic. The current goal of scaling up programmes based on preventive chemotherapy (PCT) will alter to sustaining NTD prevention, through sensitive surveillance and rapid response to resurgence. A new suite of tools and approaches will be required for both PCT and Intensive Disease Management (IDM) diseases in this timeframe to enable disease endemic countries to: 1. Sensitively and sustainably survey NTD transmission and prevalence in order to identify and respond quickly to resurgence. 2. Set relevant control targets based not only on epidemiological indicators but also entomological and ecological metrics and use decision support technology to help meet those targets. 3. Implement verified and cost-effective tools to prevent transmission throughout the elimination phase. Liverpool School of Tropical Medicine (LSTM) and partners propose to evaluate and implement existing tools from other disease systems as well as new tools in the pipeline in order to support endemic country ownership in NTD decision-making during the elimination phase and beyond.

Liquid chromatography-mass spectrometry analysis of diethylcarbamazine in human plasma for clinical pharmacokinetic studies.

A sensitive and selective liquid chromatographic method using mass spectrometric detection was developed for the determination of diethylcarbamazine (DEC) in human plasma. DEC and its stable isotope internal standard d3-DEC were extracted from 0.25mL of human plasma using solid phase extraction. Chromatography was performed using a Phenomenex Synergi 4µ Fusion-RP column (2mm×250mm) with gradient elution. The retention time was approximately 4.8min. The assay was linear from 4 to 2200ng/mL. Analysis of quality control samples at 12, 300, and 1700ng/mL (N=15) had interday coefficients of variation of 8.4%, 5.4%, and 6.2%, respectively (N=15). Interday bias results were -2.2%, 6.0%, and 0.8%, respectively. Recovery of DEC from plasma ranged from 84.2% to 90.1%. The method was successfully applied to clinical samples from patients with lymphatic filariasis from a drug-drug interaction study between DEC and albendazole and/or ivermectin.

Underpinning sustainable vector control through informed insecticide resistance management.

BACKGROUND: There has been rapid scale-up of malaria vector control in the last ten years. Both of the primary control strategies, long-lasting pyrethroid treated nets and indoor residual spraying, rely on the use of a limited number of insecticides. Insecticide resistance, as measured by bioassay, has rapidly increased in prevalence and has come to the forefront as an issue that needs to be addressed to maintain the sustainability of malaria control and the drive to elimination. Zambia's programme reported high levels of resistance to the insecticides it used in 2010, and, as a result, increased its investment in resistance monitoring to support informed resistance management decisions. METHODOLOGY/PRINCIPAL FINDINGS: A country-wide survey on insecticide resistance in Zambian malaria vectors was performed using WHO bioassays to detect resistant phenotypes. Molecular techniques were used to detect target-site mutations and microarray to detect metabolic resistance mechanisms. Anopheles gambiae s.s. was resistant to pyrethroids, DDT and carbamates, with potential organophosphate resistance in one population. The resistant phenotypes were conferred by both target-site and metabolic mechanisms. Anopheles funestus s.s. was largely resistant to pyrethroids and carbamates, with potential resistance to DDT in two locations. The resistant phenotypes were conferred by elevated levels of cytochrome p450s. CONCLUSIONS/SIGNIFICANCE: Currently, the Zambia National Malaria Control Centre is using these results to inform their vector control strategy. The methods employed here can serve as a template to all malaria-endemic countries striving to create a sustainable insecticide resistance management plan.

Long-lasting insecticidal nets remain efficacious after five years of use in Papua New Guinea.

Long-lasting insecticide-treated nets (LLINs) have been distributed throughout Papua New Guinea since 2004 as part of the country's malaria control program. This study aimed to evaluate the efficacy of these used bednets over time and with respect to the various household factors related to their use in order to enable the National Department of Health to maximize on the benefits of LLINs. In 2008 and early 2009, used LLINs (0-9 years old) were collected in various villages in Papua New Guinea as part of the Global Fund to Fight AIDS, Tuberculosis and Malaria (GFATM)-supported National Malaria Control Program and data were collected on net usage. A subset of the nets were tested for residual insecticide content. Net efficacy was measured by the rate of knockdown of Anopheles farauti s.s. following exposure to LLINs using the World Health Organization cone bioassay. Optimal effectiveness (> 95% knockdown 1 hour post exposure) was observed in 92% of the LLINs. A slight reduction in efficacy was observed after two years of household use and there was a significant relationship between the number of years in use and percent knockdown (p < 0.001) as well as deltamethrin concentration (p < 0.001). Washing of nets was not associated with a reduction in deltamethrin concentration, but drying them in the sun was (p = 0.008). The physical conditions of these nets also degraded over time with a significant increase in the number of large holes after 5 years (p = 0.02). These findings are in support of the current recommendation to replace LLINs after five years of use, and demonstrate that proper net care can extend the length of efficacy.

Mosquito-parasite interactions can shape filariasis transmission dynamics and impact elimination programs.

The relationship between mosquito vectors and lymphatic filariasis (LF) parasites can result in a range of transmission outcomes. Anophelines are generally characterized as poor vectors due to an inability to support development at low densities. However, it is important to understand the potential for transmission in natural vectors to maximize the success of elimination efforts. Primary vectors in Papua New Guinea (n = 1209) were dissected following exposure to microfilaremic blood (range 8-233 mf/20 µl). We examined density dependent and species-specific parasite prevalence, intensity and yield, barriers to parasite development as well as impacts on mosquito survival. We observed strikingly different parasite prevalence and yield among closely related species. Prevalence of infective stage larvae (L3s) ranged from 4.2% to 23.7% in An. punctulatus, 24.5% to 68.6% in An. farauti s.s. and 61.9% to 100% in An. hinesorum at low and high density exposures, respectively. Injection experiments revealed the greatest barrier to parasite development involved passage from the midgut into the hemocoel. The ratio of L3 to ingested mf at low densities was higher in An. hinesorum (yield = 1.0) and An. farauti s.s. (yield = 0.5) than has been reported in other anopheline vectors. There was a negative relationship between mosquito survival and bloodmeal mf density. In An. farauti s.s., increased parasite yield and survival at low densities suggest greater competence at low microfilaremias. In Papua New Guinea the likelihood of transmission will be strongly influenced by vector composition and changes in the mf reservoir as a result of elimination efforts. Global elimination efforts will be strengthened by the knowledge of transmission potential in the context of current control measures.

Insecticidal bed nets and filariasis transmission in Papua New Guinea.

BACKGROUND: Global efforts to eliminate lymphatic filariasis are based on the annual mass administration of antifilarial drugs to reduce the microfilaria reservoir available to the mosquito vector. Insecticide-treated bed nets are being widely used in areas in which filariasis and malaria are coendemic. METHODS: We studied five villages in which five annual mass administrations of antifilarial drugs, which were completed in 1998, reduced the transmission of Wuchereria bancrofti, one of the nematodes that cause lymphatic filariasis. A total of 21,899 anopheles mosquitoes were collected for 26 months before and 11 to 36 months after bed nets treated with long-lasting insecticide were distributed in 2009. We evaluated the status of filarial infection and the presence of W. bancrofti DNA in anopheline mosquitoes before and after the introduction of insecticide-treated bed nets. We then used a model of population dynamics to estimate the probabilities of transmission cessation. RESULTS: Village-specific rates of bites from anopheline mosquitoes ranged from 6.4 to 61.3 bites per person per day before the bed-net distribution and from 1.1 to 9.4 bites for 11 months after distribution (P<0.001). During the same period, the rate of detection of W. bancrofti in anopheline mosquitoes decreased from 1.8% to 0.4% (P=0.005), and the rate of detection of filarial DNA decreased from 19.4% to 14.9% (P=0.13). The annual transmission potential was 5 to 325 infective larvae inoculated per person per year before the bed-net distribution and 0 after the distribution. Among all five villages with a prevalence of microfilariae of 2 to 38%, the probability of transmission cessation increased from less than 1.0% before the bed-net distribution to a range of 4.9 to 95% in the 11 months after distribution. CONCLUSIONS: Vector control with insecticide-treated bed nets is a valuable tool for W. bancrofti elimination in areas in which anopheline mosquitoes transmit the parasite. (Funded by the U.S. Public Health Service and the National Institutes of Health.).

Pyrethroid susceptibility in natural populations of the Anopheles punctulatus group (Diptera: Culicidae) in Papua New Guinea.

The development of insecticide resistance has compromised mosquito control efforts in many parts of the world. Papua New Guinea (PNG) has a long history of dichlorodiphenyltrichloroethane (DDT) use and currently distributes pyrethroid-treated nets for malaria control. This study is the first to investigate the status of pyrethroid resistance in the Anopheles punctulatus group, the major malaria and filariasis vectors of PNG. The study used World Health Organization standard susceptibility bioassays to detect knockdown phenotypes and a novel nested polymerase chain reaction to detect the knockdown resistant (kdr) allele in these vectors. Our results show 100% susceptibility to pyrethroids in all populations surveyed and an absence of the kdr allele.