Household use of insecticide consumer products in a dengue-endemic area in México

Use of Household Insecticides against Mosquitoes in Dengue-Endemic Areas in Sri Lanka

The use of household insecticides in the formulation of mosquito coils and vaporizers is common among the public to protect against mosquito-borne diseases. However, information regarding the use of these commonly practiced household insecticides is scarce in Sri Lanka. A questionnaire-based survey was directed to 600 households in Colombo, Gampaha, Kandy, Kalutara, Jaffna, and Galle districts in Sri Lanka. Household insecticides were used by the majority of the respondents (57.0%), and electric liquid vaporizers (46.7%) and mosquito coils (45.7%) were the commonly used forms. The active ingredients in mosquito coils were d-trans-allethrin (w/w 0.12%), metofluthrin (w/w 0.005%), and dimefluthrin (w/w 0.01%); in liquid vaporizers, they were prallethrin (w/v 1.24% and w/v 1.26%) and transfluthrin (w/v 0.9%). The majority of the household insecticide consumers were moderately satisfied with the effectiveness of the products (68.6%), and most of the participants used household insecticides daily (35.5%), especially during the evening (41.6%). Most of the consumers were unaware of the chemicals included in household insecticides (62.8%). Mosquito coils were abundantly used by rural area participants (75.8%), whereas liquid vaporizers were the most common among the urban participants (56.4%). The findings indicate that demographic and socioeconomic factors influence household insecticide practices. To our knowledge, this study reveals the use of household insecticides to control mosquitoes for the first time in Sri Lanka and highlights the importance of awareness programs and the proper utilization of these products.

Pyrethroid susceptibility reversal in Aedes aegypti: A longitudinal study in Tapachula, Mexico

Pyrethroid resistance in Aedes aegypti has become widespread after almost two decades of frequent applications to reduce the transmission of mosquito-borne diseases. Because few insecticide classes are available for public health use, insecticide resistance management (IRM) is proposed as a strategy to retain their use. A key hypothesis of IRM assumes that negative fitness is associated with resistance, and when insecticides are removed from use, susceptibility is restored. In Tapachula, Mexico, pyrethroids (PYRs) were used exclusively by dengue control programs for 15 years, thereby contributing to selection for high PYR resistance in mosquitoes and failure in dengue control. In 2013, PYRs were replaced by organophosphates-insecticides from a class with a different mode of action. To test the hypothesis that PYR resistance is reversed in the absence of PYRs, we monitored Ae. aegypti's PYR resistance from 2016 to 2021 in Tapachula. We observed significant declining rates in the lethal concentration 50 (LC50), for permethrin and deltamethrin. For each month following the discontinuation of PYR use by vector control programs, we observed increases in the odds of mosquitoes dying by 1.5% and 8.4% for permethrin and deltamethrin, respectively. Also, knockdown-resistance mutations (kdr) in the voltage-gated sodium channel explained the variation in the permethrin LC50s, whereas variation in the deltamethrin LC50s was only explained by time. This trend was rapidly offset by application of a mixture of neonicotinoid and PYRs by vector control programs. Our results suggest that IRM strategies can be used to reverse PYR resistance in Ae. aegypti; however, long-term commitment by operational and community programs will be required for success.

Improving the efficiency of aerosolized insecticide testing against mosquitoes

Developing robust and standardised approaches for testing mosquito populations against insecticides is vital for understanding the effectiveness of new active ingredients or formulations. Methods for testing mosquito susceptibility against contact insecticides or products, such as those delivered through public health programmes, are well-established and standardised. Nevertheless, approaches for testing volatile or aerosolized insecticides used in household products can be challenging to implement efficiently. We adapted WHO guidelines for household insecticides to develop a standardised and higher-throughput methodology for testing aerosolized products in a Peet Grady test chamber (PG-chamber) using caged mosquitoes and an efficient decontamination method. The new approach was validated using insecticide resistant and susceptible Aedes and Anopheles mosquito colonies. An added feature is the inclusion of cage-facing cameras to allow real-time quantification of knockdown following insecticide exposure. The wipe-based decontamination method was highly effective for removing pyrethroids' aerosolized oil-based residues from chamber surfaces, with < 2% mortality recorded for susceptible mosquitoes tested directly on the surfaces. There was no spatial heterogeneity for knockdown or mortality of caged mosquitoes within the PG chamber. The dual-cage approach we implement yields eight-times the throughput compared to a free-flight protocol, allows simultaneous testing of different mosquito strains and effectively discriminates susceptible and resistant mosquito colonies tested side-by-side.

A Systematic Review of Mathematical Models of Dengue Transmission and Vector Control: 2010-2020

Vector control methods are considered effective in averting dengue transmission. However, several factors may modify their impact. Of these controls, chemical methods, in the long run, may increase mosquitoes' resistance to chemicides, thereby decreasing control efficacy. The biological methods, which may be self-sustaining and very effective, could be hampered by seasonality or heatwaves (resulting in, e.g., loss of Wolbachia infection). The environmental methods that could be more effective than the chemical methods are under-investigated. In this study, a systematic review is conducted to explore the present understanding of the effectiveness of vector control approaches via dengue transmission models.

Assessing health-seeking behaviour and malaria prevention practices among communities in four districts of the Volta Region of Ghana

Background

Malaria is a preventable disease that causes huge morbidity and mortality in malaria-endemic areas, especially among children and pregnant women. The malaria control programme focuses on the prevention of mosquito bites using insecticide-treated nets (ITNs) and mosquito aerosol sprays and coils, as well as prevention of severe disease among those infected through prompt and adequate treatment. The success of the malaria control programme in Ghana is dependent on the malaria prevention practices of people in the community. Therefore, this study evaluated the malaria prevention practices of participants in four districts of the Volta Region of Ghana.

Methods

This was a cross-sectional study conducted in Ketu South, Nkwanta South, Hohoe Municipality and Ho West districts of the Volta Region of Ghana. Questionnaire were administered to adults who consented to each household visited. Questions were asked on the socio-demographics and malaria prevention practices of the households. Data analysis was done using SPSS version 23 with frequency distribution done for all the variables. Pearson chi-square was used to determine the significant association between socio-demographics and malaria prevention practices, and Multivariate nominal logistic regression analysis was used to model the relationship between dichotomous dependent variables (ITN ownership and usage) and independent variables.

Results

Out of the 2493 participants; 2234 (89.6%) owned ITN and 1528 (68.4%) used ITN a night before this study, 768 (30.8%) used mosquito aerosol spray and 368 (15%) used mosquito coil. More females significantly owned ITN than males (1293, 92.4%, p ≤ 0.001). Participants from Ketu South had 1.5 times higher odds of owning an ITN compared to Ho West whose odds are not different from Nkwanta South or Hohoe (AOR, 1.56 [95% 1.09–2.22]; p = 0.01). In terms of ITN usage, participants in Nkwanta South were less likely to use ITN compared to the other districts; AOR, 0.434 [95% CI 0.31–0.62, p < 0.001]. Also, of the 668 participants that had a fever within the past 3 days, 268 (40.1%) visited a patent medicine store and 156 (23.4%) visited health facilities.

Conclusion

There is high ownership of ITNs, but relatively low utilization among the community members. Education on malaria prevention practices should be intensified and continuous among the population of the Volta Region to ensure the success of malaria control in the region.

Insecticide resistance in Aedes aegypti from Tapachula, Mexico: Spatial variation and response to historical insecticide use

BACKGROUND

Insecticide use continues as the main strategy to control Aedes aegypti, the vector of dengue, Zika, chikungunya, and yellow fever. In the city of Tapachula, Mexico, mosquito control programs switched from pyrethroids to organophosphates for outdoor spatial spraying in 2013. Additionally, the spraying scheme switched from total coverage to focused control, prioritizing areas with higher entomological-virological risk. Five years after this strategy had been implemented, we evaluated the status and variability of insecticide resistance among Ae. aegypti collected at 26 sites in Tapachula.

METHODOLOGY/PRINCIPAL FINDINGS

We determined the lethal concentrations at 50% of the tested populations (LC50) using a bottle bioassay, and then, we calculated the resistance ratio (RR) relative to the susceptible New Orleans strain. Permethrin and deltamethrin (pyrethroids), chlorpyrifos and malathion (organophosphates), and bendiocarb (carbamate) were tested. The frequencies of the substitutions V1016I and F1534C, which are in the voltage-gated sodium channel and confer knockdown-resistance (kdr) to pyrethroid insecticides, were calculated. Despite 5 years having passed since the removal of pyrethroids from the control programs, Ae. aegypti remained highly resistant to permethrin and deltamethrin (RR > 10-fold). In addition, following 5 years of chlorpyrifos use, mosquitoes at 15 of 26 sites showed moderate resistance to chlorpyrifos (5- to 10-fold), and the mosquitoes from one site were highly resistant. All sites had low resistance to malathion (< 5-fold). Resistance to bendiocarb was low at 19 sites, moderate at five, and high at two. Frequencies of the V1016I ranged from 0.16-0.71, while C1534 approached fixation at 23 sites (0.8-1). Resistance profiles and kdr allele frequencies varied across Tapachula. The variability was not associated with a spatial pattern at the scale of the sampling.

CONCLUSION/SIGNIFICANCE

Mosquito populations respond to selection pressure at a focal scale in the field. Spatial variation across sites highlights the importance of testing multiple sites within geographical regions.

Misuse, perceived risk, and safety issues of household insecticides: Qualitative findings from focus groups in Arequipa, Peru

BACKGROUND

The current body of research on insecticide use in Peru deals primarily with application of insecticides offered through Ministry of Health-led campaigns against vector-borne disease. However, there is a gap in the literature regarding the individual use, choice and perceptions of insecticides which may influence uptake of public health-based vector control initiatives and contribute to the thousands of deaths annually from acute pesticide poisoning in Peru.

METHODS

Residents (n = 49) of the Alto Selva Alegre and CC districts of peri-urban Arequipa participated in seven focus group discussions (FGD). Using a FGD guide, two facilitators led the discussion and conducted a role-playing activity. this activity, participants insecticides (represented by printed photos of insecticides available locally) and pretended to "sell" the insecticides to other participants, including describing their qualities as though they were advertising the insecticide. The exercise was designed to elicit perceptions of currently available insecticides. The focus groups also included questions about participants' preferences, use and experiences related to insecticides outside the context of this activity. Focus group content was transcribed, and qualitative data were analyzed with Atlas.ti and coded using an inductive process to generate major themes related to use and choice of insecticides, and perceived risks associated with insecticide use.

RESULTS

The perceived risks associated with insecticides included both short- and long-term health impacts, and safety for children emerged as a priority. However, in some cases insecticides were reportedly applied in high-risk ways including application of insecticides directly to children and bedding. Some participants attempted to reduce the risk of insecticide use with informal, potentially ineffective personal protective equipment and by timing application when household members were away. Valued insecticide characteristics, such as strength and effectiveness, were often associated with negative characteristics such as odor and health impacts. "Agropecuarios" (agricultural supply stores) were considered a trusted source of information about insecticides and their health risks.

CONCLUSIONS

It is crucial to characterize misuse and perceptions of health impacts and risks of insecticides at the local level, as well as to find common themes and patterns across populations to inform national and regional programs to prevent acute insecticide poisoning and increase community participation in insecticide-based vector control campaigns. We detected risky practices and beliefs about personal protective equipment, risk indicators, and safety levels that could inform such preventive campaigns, as well as trusted information sources such as agricultural stores for partnerships in disseminating information.

Evaluating Over-the-Counter Household Insecticide Aerosols for Rapid Vector Control of Pyrethroid-Resistant Aedes aegypti

Vector control methods that mobilize and impact rapidly during dengue, Zika, and chikungunya outbreaks are urgently needed in urban contexts. We investigated whether one person using a handheld aerosolized insecticide could achieve efficacy levels comparable to targeted indoor residual spraying (TIRS), using pyrethroid-resistant Aedes aegypti in a semi-field setting with experimental houses in Mexico. The insecticide product (H24, a carbamate and pyrethroid mixture), available over-the-counter locally, was sprayed only on known Ae. aegypti-resting surfaces, for example, walls less than 1.5 m and dark hidden areas. In six identical houses with paired bedrooms, one bedroom was treated, and the other remained an untreated control. Each week for 8 weeks, 100 female pyrethroid-resistant Ae. aegypti were released in each bedroom and followed up daily. Mortality rates in treated bedrooms exceeded 90% for at least 2 weeks, and more than 80% (89.2; 95% CI: 79.98-98.35) for 3 weeks or more. Mortality rates in control houses were zero. Results demonstrate that the immediate impact of TIRS can be delivered by one person using existing products, at an estimated cost for the average household in Mexico of under US$3 per month. Triggered by early outbreak signs, dissemination via community hubs and mass/social media of instructions to treat the home immediately, with monthly re-treatment thereafter, provides a simple means to engage and empower householders. Compatible with integrated vector management strategies, it enables self-protection even if existing agencies falter, a situation exemplified by the potential impact on vector control of the restrictions imposed during the 2020 COVID-19 pandemic.

Kdr genotyping in Aedes aegypti from Brazil on a nation-wide scale from 2017 to 2018

Insecticide resistance is currently a threat to the control of Aedes agypti, the main vector of arboviruses in urban centers. Mutations in the voltage gated sodium channel (NaV), known as kdr (knockdown resistance), constitute an important selection mechanism for resistance against pyrethroids. In the present study, we investigated the kdr distribution for the Val1016Ile and Phe1534Cys alterations in Ae. aegypti from 123 Brazilian municipalities, based on SNP genotyping assays in over 5,500 mosquitoes. The alleles NaVS (1016Val+ + 1534Phe+), NaVR1 (1016Val+ + 1534Cyskdr) and NaVR2 (1016Ilekdr + 1534Cyskdr) were consistently observed, whereas kdr alleles have rapidly spread and increased in frequency. NaVS was the less frequent allele, mostly found in Northeastern populations. The highest allelic frequencies were observed for NaVR1, especially in the North, which was fixed in one Amazonian population. The double kdr NaVR2 was more prevalent in the Central-west and South-eastern populations. We introduce the 'kdr index', which revealed significant spatial patterns highlighting two to three distinct Brazilian regions. The 410L kdr mutation was additionally evaluated in 25 localities, evidencing that it generally occurs in the NaVR2 allele. This nationwide screening of a genetic mechanism for insecticide resistance is an important indication on how pyrethroid resistance in Ae. aegypti is evolving in Brazil.

Bio-Efficacy of Commercially Available Residual Insecticides for the Control of Aedes aegypti in Mexico

Commercial aerosolized insecticides can be implemented as a community-based approach to targeted indoor residual spraying against Aedes aegypti, but their efficacy on pyrethroid-resistant mosquitoes has not yet been evaluated. Two commercial aerosolized products (H24 Poder Fulminante Ultra Eficaz^®, carbamate, and Baygon Ultra Verde^®, pyrethroid) were sprayed on common indoor surfaces e.g., cement, plywood, and cloth, and tested for their residual efficacy on susceptible and field-derived pyrethroid-resistant Ae. aegypti strains using the WHO cone bioassays. Overall, ≥80% 24-h mortality was observed for both products for at least 4 wk regardless of the mosquito strain or surface type used. H24 Poder Fulminante Ultra Eficaz showed the highest residual potency, sustaining >80% mortality for 7-wk posttreatment regardless of mosquito strain and surface type. For Baygon Ultra Verde, the mean mortality of female Ae. aegypti remained >80% for a shorter period (4-6 wk). Nonpyrethroid commercial aerosolized formulations can provide a lasting residual effect indoors compatible with the need for rapid and lasting mosquito control during outbreaks and may be suitable for community-based targeted indoor residual spraying.

Fine-scale spatial and temporal dynamics of kdr haplotypes in Aedes aegypti from Mexico

BACKGROUND

As resistance to insecticides increases in disease vectors, it has become exceedingly important to monitor populations for susceptibility. Most studies of field populations of Aedes aegypti have largely characterized resistance patterns at the spatial scale of the city or country, which may not be completely informative given that insecticide application occurs at the scale of the house or city block. Phenotypic resistance to pyrethroids dominates in Ae. aegypti, and it has been partially explained by mutations in the voltage-gated sodium channel gene. Here, we assess community-level patterns of four knockdown resistance (kdr) haplotypes (C1534/I1016, F1534/I1016, C1534/V1016 and F1534/V1016) in Ae. aegypti in 24 randomly chosen city blocks from a city in Yucatán State, Mexico, during both the dry and wet season and over two years.

RESULTS

Three of the four haplotypes, C1534/I1016, C1534/V1016 and F1534/V1016 were heterogeneous between city blocks at all four sampling time points, and the double mutant haplotype, C1534/I1016, showed a significant increase following the wet season. The F1534/I1016 haplotype was rarely detected, similar to other studies. However, when haplotype frequencies were aggregated to a coarser spatial scale, the differences in space and time were obscured.

CONCLUSIONS

Our results provide empirical evidence that the selection of kdr alleles is occurring at fine spatial scales, indicating that future studies should include this scale to better understand evolutionary processes of resistance in natural populations.

Frequency of the L1014F Mutation in the Sodium Channel Gene, in Culex quinquefasciatus (Diptera: Culicidae) Populations From Rural and Urban Areas of Yucatan State, Mexico

Culex quinquefasciatus Say (Diptera: Culicidae) is a mosquito species that has attracted a lot of attention from a medical and veterinary point of view; however, little is known about the frequency of L1014F mutations that have been found in the sodium channel gene, with this being a target for DDT and pyrethroid insecticides. The distribution and frequency of the L1014F mutation in Cx. quinquefasciatus populations was determined in rural and urban areas of Yucatan, Mexico from January 2015 to March 2016. Nine hundred fifty adult females out of 17,727 immature states were collected and analyzed in all sites sampled (n = 10). Susceptible homozygotes were identified (L1014/L1014) in 12% (114/950), heterozygous individuals (F1014/L1014) in 34% (323/950), and mutated homozygotes (F1014/F1014) in 54% (513/950) during the dry and rainy seasons. In this work, study areas with a high frequency of L1014F mutation were identified. These findings may help guarantee a more effective and efficient use of the resources available for the control of this vector.

Experimental evaluation of the impact of household aerosolized insecticides on pyrethroid resistant Aedes aegypti

The extensive reliance on insecticides to control Aedes aegypti mosquitoes and disrupt transmission of dengue, chikungunya and Zika has fueled the emergence of widespread resistance to insecticides. Mismatch between the frequency of pyrethroid resistance in mosquitoes and the occurrence of pyrethroid-based insecticide applications for vector control is often hypothesized to be due to household use of commercial insecticide products. We experimentally quantified phenotypic and genotypic responses of four Ae. aegypti strains (three field, pyrethroid resistant, and one laboratory, pyrethroid susceptible) after exposure to two commonly used household aerosol insecticide products (a space spray and a residual spray formulation) containing pyrethroid active ingredients. Experiments were performed within homes of Mérida, Mexico. After exposure to the products, all three pyrethroid resistant field Ae. aegypti strains had significantly lower mortality rates (averaging 41% and 50% for the two products, respectively) than the controls (99%). Applying insecticides as surface sprays led to a significant increase in the frequency of I1016 kdr homozygotes in surviving Ae. aegypti, suggesting strong selection pressure for this allele. Given the large-scale use of household aerosol insecticide products in areas that are endemic for Ae. aegypti–transmitted diseases, their role as a pyrethroid resistance selection source, particularly when used as space sprays, should be taken into consideration when designing resistance management plans.

Efficacy of 13 Commercial Household Aerosol Insecticides Against Aedes aegypti (Diptera: Culicidae) From Morelos, Mexico

In Mexico, Aedes aegypti (L.) (Diptera: Culicidae) is the primary vector of Dengue, Zika, and Chikungunya viruses. Control programs include community participation using personal protection such as household aerosol insecticides. In both, urban or rural areas, the use of aerosol insecticides is a common practice to avoiding mosquito biting. Thus, information on the efficacy of commercial products must be available. This study reports the efficacy of 13 household aerosol insecticides against Ae. aegypti from an endemic dengue area in Mexico. To test each insecticide, six netting cages, containing 10 non-blood fed female mosquitoes each one, were placed in different locations inside a bedroom. Readings at 30 min and 24 h after exposure were recorded. No products showed 100% mortality after 30 min of exposure. Only three products killed the 100% of the individuals 24 h after exposure. Results showed a high mortality variance among insecticides. Location in the room also impacts the insecticide efficacy. Mosquitoes located inside cabinets or with behind an obstacle (preventing an accurate insecticide exposure) showed lower mortalities. Products and spraying methods could and should be improved.

Cost-effectiveness of dengue vaccination in Yucatán, Mexico using a dynamic dengue transmission model

Background

The incidence of dengue fever (DF) is steadily increasing in Mexico, burdening health systems with consequent morbidities and mortalities. On December 9^th, 2015, Mexico became the first country for which the dengue vaccine was approved for use. In anticipation of a vaccine rollout, analysis of the cost-effectiveness of the dengue vaccination program that quantifies the dynamics of disease transmission is essential.

Methods

We developed a dynamic transmission model of dengue in Yucatán, Mexico and its proposed vaccination program to incorporate herd immunity into our analysis of cost-effectiveness analysis. Our model also incorporates important characteristics of dengue epidemiology, such as clinical cross-immunity and susceptibility enhancement upon secondary infection. Using our model, we evaluated the cost-effectiveness and economic impact of an imperfect dengue vaccine in Yucatán, Mexico.

Conclusions

Our study indicates that a dengue vaccination program would prevent 90% of cases of symptomatic DF incidence as well as 90% of dengue hemorrhagic fever (DHF) incidence and dengue-related deaths annually. We conclude that a dengue vaccine program in Yucatán, Mexico would be very cost-effective as long as the vaccination cost per individual is less than $140 and $214 from health care and societal perspectives, respectively. Furthermore, at an exemplary vaccination cost of $250 USD per individual on average, dengue vaccination is likely to be cost-effective 43% and 88% of the time from health care and societal perspectives, respectively.