Wash resistance and bioefficacy of Olyset net--a long-lasting insecticide-treated mosquito net against malaria vectors and nontarget household pests

Laboratory and semi-field efficacy evaluation of permethrin-piperonyl butoxide treated blankets against pyrethroid-resistant malaria vectors

To control pyrethroid-resistant malaria vectors, Indoor Residual Spraying (IRS) and Long-Lasting Insecticidal Nets (LLINs) that include additional ingredients to pyrethroid are being developed. Same progress needs to be made to the pyrethroid-treated blankets, which are more compatible with shelter structures found in emergency settings such as displaced populations. In the current study, efficacy of blankets treated with permethrin and piperonyl butoxide (PBO) was evaluated against pyrethroid-resistant Anopheles gambiae sensu stricto. Efficacy was compared with that of Olyset LLIN, Olyset Plus LLIN and untreated blanket in terms of mortality and blood-feeding inhibition against pyrethroid-resistant Anopheles gambiae mosquitoes. The current study indicates that, in emergency shelters such as migrant and refugee camps where LLINs cannot be used, PBO-permethrin blankets may provide protection against resistant mosquitoes if widely used. No side effects related to the use of the treated blankets were reported from the participants. These results need validation in a large-scale field trial to assess the epidemiological impact of the intervention, durability and acceptability of this new vector control strategy for malaria vector control.

Evaluation of the residual efficacy and physical durability of five long-lasting insecticidal nets (LLINs) in Senegal

BACKGROUND

The preventive and curative strategies of malaria are based on promoting the use of long-lasting insecticidal nets (LLINs) and treating confirmed cases with artemisinin-based combination therapy. These strategies have led to a sharp decline in the burden of malaria, which remains a significant public health problem in sub-Saharan countries. The objective of this study was to determine and compare the residual efficacy of LLINs recommended by the World Health Organization.

METHODS

The study was conducted in six villages in two sites in Senegal located in the Sahelo-Sudanian area of the Thiès region, 70 km from Dakar and in Mbagame, a semi-urban zone in the Senegal River Valley. A census was conducted of all sleeping places in each household to be covered by LLINs. Five brands of LLIN were distributed, and every six months, retention rates, net use, maintenance, physical integrity, insecticide chemical content, and biological efficacy were examined for each type of LLIN.

RESULTS

A total of 3012 LLINs were distributed in 1249 households in both sites, with an average coverage rate of 94% (95% CI 92.68-95.3). After 36 months, the average retention rate was 12.5% and this rate was respectively 20.5%, 15.1%, 10%, 7%, and 3% for Olyset Net^®, Dawa Plus^® 2.0, PermaNet^® 2.0, NetProtect^® and Life Net^®, respectively. The proportion of LLINs with holes and the average number of holes per mosquito net increased significantly during each follow-up, with a large predominance of size 1 (small) holes for all types of LLINs distributed. During the three-year follow-up, bioassay mortality rates of a susceptible strain of insectary reared Anopheles coluzzii decreased in the following net types: in Dawa Plus^® 2.0 (100% to 51.7%), PermaNet^® 2.0 (96.6% to 83%), and Olyset Net^® (96.6% to 33.3%). Mortality rates remained at 100% in Life Net^® over the same time period. After 36 months, the average insecticide content per brand of LLIN decreased by 40.9% for Dawa Plus^® 2.0, 31% for PermaNet^® 2.0, 39.6% for NetProtect^® and 51.9% for Olyset Net^® and 40.1% for Life Net.

CONCLUSIONS

Although some net types retained sufficient insecticidal activity, based on all durability parameters measured, none of the net types survived longer than 2 years.

A colorimetric test for the evaluation of the insecticide content of LLINs used on Bioko Island, Equatorial Guinea

Background

Insecticide-treated nets and indoor residual spraying of insecticides are used as the vector control interventions in the fight against malaria. Measuring the actual amount of deposits of insecticides on bed nets and walls is essential for evaluating the quality and effectiveness of the intervention. A colorimetric “Test Kit” designed for use as a screening tool, able to detect the type II pyrethroids on fabrics and sprayed walls, was used for the first time to detect deltamethrin on long-lasting insecticidal nets (LLINs) deployed on Bioko Island, Equatorial Guinea.

Methods

LLINs were analysed using the colorimetric Test Kit performed in situ, which leads to the formation of an orange-red solution whose depth of colour indicates the amount of type II pyrethroid on the net. The kit results were validated by measuring the amount of extracted insecticide using high-performance liquid chromatography (HPLC) with diode array detection (DAD).

Results

Deltamethrin concentration was determined for 130 LLINs by HPLC–DAD. The deltamethrin concentration of these nets exhibited a significant decrease with the age of the net from 65 mg/m² (< 12 months of use) to 31 mg/m² (> 48 months; p < 0.001). Overall, 18% of the nets being used in households had < 15 mg/m² of deltamethrin, thus falling into the “Fail” category as assessed by the colorimetric Test Kit. This was supported by determining the bio-efficacy of the nets using the WHO recommended cone bioassays. The Test Kit was field evaluated in situ and found to be rapid, accurate, and easy to use by people without laboratory training. The Test Kit was shown to have a reliable linear relationship between the depth of colour produced and deltamethrin concentration (R² = 0.9135).

Conclusion

This study shows that this colorimetric test was a reliable method to assess the insecticidal content of LLINs under operational conditions. The Test Kit provides immediate results and offers a rapid, inexpensive, field-friendly alternative to the complicated and costly methods such as HPLC and WHO cone bioassays which also need specialist staff. Thus, enabling National Malaria Control Programmes to gain access to effective and affordable monitoring tools for use in situ.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12936-021-03967-w.

Control of Cockroaches (Blattaria) in Sewers: A Practical Approach Systematic Review

Periplaneta americana (L.) (Blattaria: Blattidae), the American cockroach, is the most important invasive urban pest of sewer environments colonizing there with high significance of human public health and household allergens need to be controlled. Therefore this practical approach systematic review perform internationally to highlight and provide a detailed P. americana control in sewers. Of the 474 papers, 129 papers were selected to become this practical approach systematic review study of cockroach control in sewers. To control the American cockroaches, many studies have been conducted in various fields describing from an angle. The results were classified and discussed in getting cockroaches from sewers into buildings and their elimination, insecticide susceptibility, application of dust, bait and Inesfly paint insecticide formulations, biocontrol, and futuristic action categories. A recommending manner to achieve a successful P. americana cockroach control in sewers is using a combination of Integrated Pest Management (IPM) strategies resulted in significant reductions of cockroach infestations and asthma health outcomes. Use of P. americana breeding thelytoky, push-pull strategies and an automated sewer robot, and integrating health into the future buildings may be new approaches of P. americana control strategies.

Imaging and quantitative analysis of insecticide in mosquito net fibers using Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS)

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) analysis was used to qualitatively and quantitatively assess the distribution of permethrin insecticide on the surfaces and interiors of Olyset long-lasting insecticidal net (LLIN) fibers. Total insecticide content in LLINs has been established using many analytical methods. However, it is important to quantify the bioavailable portion residing on the fiber surfaces for incorporated LLINs. ToF-SIMS is a very surface sensitive technique and can directly image the spatial distribution of permethrin insecticide on the surface of Olyset fibers. Surface permethrin appeared as patchy deposits which were easily removed by acetone and reappeared after several days as interior permethrin migrated (bloomed) from the fiber interior. After a wash/incubation cycle, permethrin deposits were more diffuse and less concentrated than those on the as-received fibers. ToF-SIMS is particularly sensitive to detect the Cl^- ion, which is the characteristic ion of permethrin. Ion implantation and quantification of dopants using SIMS is well established in the semiconductor industry. In this study, quantitative depth profiling was carried out using ³⁵Cl^- ion implantation to correlate secondary ion yield with permethrin concentration, yielding a limit of detection of 0.051 wt% for permethrin. In some cases, surface concentration differed greatly from the fiber interior (>1 μm below the surface). Two- and three-dimensional mapping of Cl at sub-micrometer resolution showed permethrin to be dissolved throughout the fiber, with about 2 vol% residing in disperse, high-concentration domains. This suggests that these fibers fall into the class of monolithic sustained-release devices. It is expected that ToF-SIMS can be a valuable tool to provide insight into the insecticide release behavior of other LLIN products, both current and future.

Assessment of Long-Lasting Insecticidal Nets (LLINs) on Vectors and Malaria Transmission in the Commune of Aguegues, Benin

INTRODUCTION

To overcome the problems of periodic re-impregnation of mosquito nets and low rates of treatment, the commune of Aguegues was chosen to evaluate the effects of Olyset(®) nets on malaria transmission and against An. gambiae.

METHODS

87 old Olyset(®) nets installed five years ago were identified in the village 'Akpadon'. 10 untreated nets were installed in 10 structures of type "a bedroom and parlour" in the village 'Akodji'. Four rooms without nets were identified in the village 'Donoukpa'. Entomological and epidemiological evaluations were conducted during the May to October 2011. 24 sessions of capture or 2088 men-nights resulted in the capture of 30,608 mosquitoes.

RESULTS

The entrance of anopheles was significantly reduced in the village with Olyset(®) nets. 45% of mosquitoes captured inside rooms with Olyset(®) nets were found dead after 24 hrs of obser-vation. Overall, parasitemia was very low in the treated village (4.52%). 18 (4.64%) cases of malaria fever were from Akpadon with 7.5% positive blade smear, 29 (10.98%) were from Akodji with 8.37% positive blade smear, and 80 (95.23%) come from Donoukpa with 38.09% positive blade smear. The Olyset(®) nets and untreated net were adjusted hemoglobin levels.

CONCLUSION

Olyset(®) net had a very high knock down effect and is an alternative in malaria control.

Residual activity and integrity of PermaNet® 2.0 after 24 months of household use in a community randomised trial of long lasting insecticidal nets against visceral leishmaniasis in India and Nepal

The World Health Organization (WHO) recommends several brands of long lasting insecticidal net (LN) for protection against insect vectors but also advises national programmes to monitor and evaluate performance under local conditions to help them select the most suitable LN for their setting. During the course of a community randomised trial of LNs against visceral leishmaniasis in northern India and Nepal, opportunity arose to assess the efficacy of PermaNet 2.0 (Vestergaard-Frandsen, Denmark) after two years of use against sandfly vectors. Between 63% (India) and 78% (Nepal) of LNs became holed over the course of two years, deltamethrin residues fell from 55 mg/m(2) to an average of 11.6 mg/m(2) (India) and 27.9 mg/m(2) (Nepal), but on the basis of bioassay criteria all LNs tested still met the WHO Pesticide Evaluation Scheme standard for LN effectiveness. Nets had on average only been washed 2.5 times (India) and 0.6 times (Nepal) by householders over the course of two years. The loss of insecticide was attributed to factors which had little or nothing to do with washing, such as handling, friction and torsion during daily use. Under conditions pertaining in this region of south Asia, and for two years at least, this brand of net continues to meet the criteria established by WHO for LNs.

Insecticides Susceptibility Status of the Bedbugs (Cimex lectularius) in a Rural Area of Magugu, Northern Tanzania

The recent spread of bedbugs, Cimex lectularius L. (Heteroptera: Cimicidae), has received attention of the public health sector for designing of effective plan of action for control. Several studies have focused on determining the distribution and abundance of bedbug populations in tropical areas. This study establishes baseline information on deltamethrin, permethrin, alphacypermethrin, lambdacypermethrin and K-O tab susceptibility status in a bedbug population collected from Magugu area in northern Tanzania. The evolution of insecticide resistance could be a primary factor in explaining this resurgence of bedbugs in many areas, both rural and urban. Evaluation of the bedbug population from houses in Magugu indicates that the population of bedbugs is susceptible to pyrethroid insecticides, which are commonly used. Without the development of new tactics for bedbug resistance management, further escalation of this public health problem should be expected when resistant gene spreads within the population. These results suggest that although all concentrations kill bedbugs, more evaluations should be done using WHO kits and mechanisms involved in pyrethroid resistance should be evaluated, such as metabolic and knockdown resistance gene, to have a broad picture for better design of control methodologies.

Wash durability and optimal drying regimen of four brands of long-lasting insecticide-treated nets after repeated washing under tropical conditions

BACKGROUND

The current study was undertaken to determine the optimal wash-drying regimen and the effects of different washing procedures on the efficacy, and durability of four brands of newly introduced long-lasting insecticide-treated nets (LLINs) under tropical conditions.

METHODS

In the current study, the following four LLINs were tested: Olyset, PermaNet 2.0, BASF and TNT. Nets were divided into three sets; one set was washed by hand rubbing and air-dried either hanging or spread on the ground in direct sunlight or hanging or spread on the ground under the shade. A second set was washed using the WHO protocol (machine) and the third set was washed by beating the nets on rocks. The biological activities of the nets were assessed by a three-minute bioassay cone test and the residual insecticide contents were determined using high performance liquid chromatography (HPLC) procedure.

RESULTS

Nets that were dried hanging under the shade retained more insecticide, 62.5% and recorded higher mortality compared to nets which were dried lying on the ground in direct sunlight 58.8%, nets dried under the shade spread on the ground 56.3%, and 57.8% for nets dried hanging in direct sunlight. It was also observed that nets washed by the standard WHO protocol, retained more insecticide and were more effective in killing mosquitoes compared to nets washed by local methods of hand rubbing and beating on rocks. There were significant differences between drying regimens (p < 0.0001) and between washing procedures (p < 0.001) respectively. However, the effect of net type was statistically insignificant. The statistical differences on individual nets were also compared, for PermaNet and TNT there were no significant differences observed between the four drying regimens (p = 0.7944 and 0.4703) respectively). For BASF and Olyset, the differences were significant (p < 0.001 and p > 0.0001).

CONCLUSION

The results of this study suggest that washing and drying regimen influence the insecticidal activity of LLINs. The standard WHOPES washing protocol underestimates the amount of insecticide washed from LLINs compared to the abrasive washing procedures that are used in the field. This suggests that there is need to educate net users to adopt a more gentle washing procedure while handling LLINs. The education should accompany net distribution campaigns.

Efficacy of permethrin treated long-lasting insecticidal nets on malaria transmission and observations on the perceived side effects, collateral benefits and human safety in a hyperendemic tribal area of Orissa, India

Studies were conducted on the efficacy of Olyset nets-a long-lasting insecticidal net (LLIN) factory treated with 2% (w/w) permethrin on malaria transmission in an area under the influence of pyrethroid susceptible vector species Anopheles culicifacies and A. fluviatilis in Sundargarh District, Orissa, India. The study area comprised 22 villages that were randomized into three clusters and designated as Olyset net, untreated net, and no net area. Malaria incidence in the study population was measured through longitudinal active surveillance at fortnightly intervals. There was a reduction of 65-70% in malaria incidence in Olyset net area as compared to the control areas. The attack rate of Plasmodium falciparum or number of episodes per person per year in different age groups also showed significant reduction in Olyset net area as compared to untreated net and no net areas. Cross-sectional point prevalence surveys showed 45.7% reduction of malaria prevalence in Olyset net users, whereas there was an increase of 33.3% and 51% in untreated net and no net villages respectively. The compliance rate of Olyset net usage in the study population was 80-98% during different months, whereas it was between 70% and 90% for untreated nets. There were minimal complains of skin irritation (4%), itching (8%) and eye irritation (1.2%). However, these effects were only transitory in nature lasting for few hours of the first usage. Olyset nets also provided collateral benefits in terms of relief not only from mosquitoes and malaria but also from other household pests such as head lice, bed bugs, cockroaches, ants and houseflies. The Olyset nets were found to be safe to humans as no adverse event was recorded in the net users that can be attributed to the use of net. The study showed that Olyset nets are effective personal protection tool that can be used in a community based intervention programme.

Acceptability, willing to purchase and use long lasting insecticide treated mosquito nets in Orissa State, India

Long lasting insecticide treated nets (LLINs) that require no re-treatment have been advocated as an effective tool against malaria transmission. However, success of this community based intervention measure largely depends on its acceptability and proper usage by the target population, besides assuring access to bed nets. To determine the acceptability of LLIN, its usage and people's willingness to buy the net, a study was conducted in two tribal districts viz., Malkangiri (with ongoing ITN programme) and Koraput (no ITN programme) of Orissa State, India. Both qualitative and quantitative data collection methods were used to collect information regarding the objective of the study. A total of 2457 LLINs (Olyset Nets) were distributed in the selected villages of these districts at free of cost. In the study villages of Malkangiri, 58% of the households had either ITNs (73%) or other types of mosquito nets aside from the LLINs and in the villages of Koraput, only 8% had other nets, as majority (96%) informed that buying nets from market was not affordable to them. Physical verification of the nets during the house visits revealed that 75.4% and 83% (in ITNs and non-ITNs villages, respectively) of the LLINs and 76% of the other nets (including ITNs) were used by the respondents, the night before the survey as nets were in a hanging position at the time of the visit. Majority of the respondents (76-98%) felt that reduction of mosquito bites as the main perceived benefit of using the LLINs. About 55% and 67% of the respondents from non-ITNs and ITNs areas, respectively, expressed their willingness to buy the LLINs. Among them, 76.8% and 94.7% offered to pay INR<100 for a net and also ready to buy it by cash payment. Social marketing of LLINs at a subsidized price or free supply to the deserving sections of people (socially/economically poor and/or under-privileged) and ensuring the availability of nets during harvesting season could encourage people to buy and use LLINs.

Wash resistance and residual efficacy of long-lasting polyester netting coated with alpha-cypermethrin (Interceptor) against malaria-transmitting mosquitoes in Assam, northeast India

Malaria is endemic in Assam, northeast India, with low-to-moderate transmission of the causative parasites, mostly by Anopheles minimus. Plasmodium falciparum is the predominant parasite (>60%), with remaining cases being due to P. vivax. As an alternative intervention for malaria control, long-lasting insecticidal nets [Interceptor coated with alpha-cypermethrin 10% suspension concentrate (SC), 0.667% w/w, 0.2g/m(2)] underwent field evaluation for laboratory wash resistance and residual efficacy in field conditions against malaria-transmitting mosquitoes. Based on entomological observations, the Interceptor net intervention was the most effective, corresponding to the lowest mosquito vector density in experimental villages. There was virtual disappearance of A. minimus in Interceptor net villages in contrast to the untreated net intervention and the no-net control. Contact cone bioassay tests revealed 100% mortality in the A.minimus group of mosquito species in the community using the Interceptor net, which was consistent during the follow-up monitoring period (October 2006 to April 2007) in field conditions. Similar levels of mortality were observed in laboratory-washed nets compared with unwashed nets, and wash resistance was consistent even after the 20th serial wash at fortnightly intervals. Community compliance and acceptance of the Interceptor net was high, with decreased nuisance due to biting mosquitoes and other household insect pests being reported.