The situation of contagious diseases transmitted by Aedes mosquitoes are a significant public health concern in Thailand. There has been a long-lasting outbreak that continues to the present day. Each year, a large number of people become sick and die, which has an economic impact, as well as the occupation of patients and their families, including government expenditures on medical treatment—many losses to the country’s socio-economy, especially dengue fever, which is transmitted by Aedes. Currently, there are no specific treatments for dengue hemorrhagic fever. Currently, there is an uncertain pattern of epidemics. In the past ten years, epidemics have occurred every other year, every two years, or every three years. In 2021, the number of patients is likely to decrease by 86% by 2020 and, including the proportion of dengue virus strains beginning to change, with the dominant DENV-2 declining, there is a chance that DEVN-3 and DEVN-4 will increase and cause outbreaks. Most people may not be immune to the strain, but the following year, there may be a large outbreak of dengue fever. The dengue fever In Thailand, in 2021, 9.956 cases of cumulative dengue fever (DF) [dengue hemorrhagic fever (DHF), and dengue shock syndrome (DSS) were reported]. The morbidity rate is 14.97 per 100,000 people. Six deaths occurred with a mortality rate of 0.06%. The cumulative number of cases was less than the previous year, 86%, and 16% less than the median in the past five years. However, in July, the number of cases was 11% higher than the median, with the northeastern region having the highest morbidity rate. The southern part has the highest mortality and mortality rates. ¹

In the case of dengue fever in Health District No.10 in 2021, there were 457 cumulative cases, a morbidity rate of 7.54 per 100.000 population, and no deaths were reported. Ubon Rachathani has the highest morbidity rate (per 100.000 population) of 12.15 (228 cases), followed by Sisaket (11.07, 163 cases), Yasothon (6.32, 34 cases), Amnat Charoen (4.23, 16 cases), and Mukdahan (3.97, 14 cases). ² The risk group for dengue fever remains the school-aged (5-14 years) group; at the same time, the age group of 15 years and older has a higher mortality rate than school-aged children, especially in adults aged 35 years and older. Their mortality rate is higher than the target (the mortality rate target is not more than 0.10%), because mature and older adults often have chronic diseases. As a result, patients infected with the dengue virus can have complicated symptoms, such as liver failure and kidney failure, that are difficult to cure, or some patients go to private clinics for their first treatment, where they may be injected with NSAIDs or steroids, causing more severe symptoms and bleeding due to the side effects of receiving such a vaccine. ³ Patients can be seen throughout the year, but this is expected during the rainy season, with the house ( Aedes aegypti) and garden mosquitoes ( Aedes albopictus) being carriers of dengue fever.

Preventive measures to control the disease have not a direct cure yet been established, and there are no vaccines available against this disease. Disease control can be achieved by reducing the population of Aedes mosquitoes. Currently, control can be performed using various methods, including environmental, biological, and chemical methods. Additionally, Aedes can propagate quickly and resist insecticides, but when an outbreak occurs, insecticides are presented to control the disease to break the life cycle and stop the outbreak of the disease; for example, thermal fogging or ultra-low volume (ULV) spraying is also an important measure to control mosquitoes that produce good results and see the results quickly. ⁴ At present, the most popular chemicals used to control mosquitoes are pyrethroids such as deltamethrin, cypermethrin, cyfluthrin, and lambda-cyhalothrin, etc., due to this chemical group is highly safe for humans and in friendly environments, and they can decompose fast-paced in natural collationed to the other chemicals. ³ In the local administrative organization sector, mosquito killers are the most significant consumers of insecticides. The purchase volume and use of various types of insecticides in all departments tends to increase annually. ⁵

The Department of Disease Control (DCD) uses deltamethrin as the primary measure for mosquito spraying in areas where dengue outbreaks occur. ⁶ According to a preliminary survey of the site, the responsibility of Health District No.10, the chemicals commonly used to manage mosquitoes are pyrethrin, deltamethrin, and cypermethrin, which are found to be effective in decreasing mature mosquitoes. ² Due to the ongoing outbreak of dengue fever, it is likely to become more severe; however, the use of chemicals to manage dengue fever remains a problem in areas where it has occurred. Therefore, this study aimed to investigate the susceptibility of mosquitoes to deltamethrin chemicals used for elimination in high-risk districts of dengue fever and to compare the effectiveness of 0.5% deltamethrin and deltamethrin + s-bio-allethrin 0.75% + piperonyl butoxide 10% (DAP) to utilize indoors and outdoors in the elimination of Aedes in high-risk districts of dengue fever. The results of this study will be used to select the concentration of chemicals, including spraying skills to limit mosquito vectors in the area, and to bring the data up to plan the scope of practical prevention of dengue fever.

Area selection was based on the scoring criteria of the Division of Communicable Diseases (DCD) transmitted by insects. The Department of Disease Control (DDC), ten high-risk districts of dengue fever, for example, Ubon Ratchathani province, consists of Ubon Ratchathani, Khong Chiam, Samrong, Kheuang Nai, Det Udom, and Thung Si Udom districts. Sisaket Province includes the Sisaket, Yang Chum Noi, and Rasi Salai districts. Aedes mosquitoes were susceptible to deltamethrin at a concentration of 0.03%. Furthermore, Aedes mosquitoes were susceptible to high levels of the tested chemicals, accounting for 50.0% in Yang Chum Noi, Samrong, Meuang Ubon Ratchathani, Det Udom, and Najaluai. The susceptibility test results for Aedes mosquitoes to deltamethrin at a concentration of 0.15% indicated high susceptibility. This trend was observed in five areas, or 100.0% of the cases, which included Khueang Nai, Thung Si Udom, Sisaket, Khong Chiam, and Rasi Salai districts ( Table 1).

The mortality rate of Aedes against 0.5% deltamethrin after 24 hours of chemical exposure indoors means 85.5 Aedes (12.62 standard deviations), and the study showed that the average mortality of outdoors means 15.4 Aedes (6.29 standard deviation); see more detail on Table 2.

The Aedes mortality rate against DAP after 24 hours of chemical exposure indoors showed an average of 93.9 (7.91 standard deviations), and it was found that the average mortality outdoors was 18.0 (6.20 standard deviation) (see Table 3).

The next part of the study compared the indoor and outdoor mortality rates in Aedes. Indoor DAP was more effective than 0.5% deltamethrin (p <0.001) (95% CI = -1.49-18.29), as shown in the following details in Table 4. Outdoor DAP was also more effective than 0.5% deltamethrin at 2.25 Aedes (95% CI= 1.55-2.94) ( Table 4).

The next part of the study compared the indoor and outdoor mortality rates of edes treated with 0.5% deltamethrin and DAP. The results showed that the 0.5% deltamethrin in eliminating indoor Aedes was higher than outdoors at 70.1 (95% CI = 63.78-76.41) and DAP mean difference of 75.9 (95% CI = 72.58-79.21) ( Table 5).

Table 1 presents data on the percentage of Aedes aegypti mortality against deltamethrin at concentrations of 0.03% and 0.15% in tested chemicals for Aedes aegypti susceptibility (n = 1,000). The table includes the number of test samples, percentage of mortality against the tested chemicals, and the level of sensitivity, tolerance, or resistance of Aedes to the tested chemicals. Table 2 compares the percentage of abdominal upside-down and mortality of Aedes aegypti against 0.5% deltamethrin indoors and outdoors. The table displays the number of mosquito species, the percentage of abdominal Aedes after 60 minutes, and the percentage of Aedes aegypti mortality at 24 hours for both indoor and outdoor environments.

Table 3 shows the percentage of abdominal upside-down and mortality of Aedes aegypti against DAP indoors and outdoors. It includes the number of mosquito species, the percentage of abdominal Aedes after 60 minutes, and the percentage of Aedes aegypti mortality at 24 hours for both indoor and outdoor environments. Table 4 compares the Aedes mortality difference between 0.5% deltamethrin and DAP indoors and outdoors. The table presents the mean difference, 95% CI, t-value, and p-value for both indoor and outdoor environments. Table 5 compares the Aedes mortality difference between indoor and outdoor 0.5% deltamethrin and DAP. It includes the mean difference, 95% CI, t-value, and p-value for both indoor and outdoor environments.

The main finding of this study is the use of deltamethrin, S-bio-allethrin, and 10% piperonyl butoxide to eliminate edes in high-risk districts demonstrated three findings. First, edes in the Ubon Ratchathani provinces (Mueang Ubon Ratchathani, Samrong, Det Udom, and Na Chaluay districts) were sensitive to 0.03% deltamethrin. In contrast, Aedes in Sisaket Province (Yang Chum Noi district) was susceptible to 0.15% deltamethrin. In Ubon Ratchathani province (Khong Chiam, Khueang Nai, and Thung Si Udom) and Sisaket province (Mueang Sisaket and Rasi Salai), the areas with a nearly yearly outbreak of dengue fever used a very high concentration exceeding the ratio specified on the label of the chemical bottle. This finding might be explained by the lack of spraying skills of the staff, who have not been trained and developed the potential before the operation. This finding is consistent with that of Moyes et al., who reported the effectiveness of chemical spraying for Aedes control in local governance. ⁷ Spraying techniques and basic sprayer restoration from the Department of Disease Control teams lack the required skills. Chemical mixing and correct spraying methods for 29.1% of sprayers and sprayer machines failed to meet the benchmark, which may make disease control ineffective. As a result, mosquitoes were not lethal and became resistant to many chemicals used. As the concentration of chemicals increased, Aedes became more resistant to chemicals in areas where larger amounts of chemicals were used. ⁸ Yahoop et al. studied the susceptibility of larvae and Aedes aegypti in the area of responsibility of the Office of Disease Prevention and Control 6, Khon Kaen Province, 2009. ⁹ The results showed that the sensitivity of adult mosquitoes to chemicals compared to the Bora bora strain found that are resistant to permethrin 0.75% in almost all areas with a mortality rate of 38–75%, deltamethrin 0.05%, and Deltamethrin 0.05% was found that majority of mosquitoes are moderate to high sensitivity (82% – 100%). Except for the Aedes outside the municipality of Roi Et province, which were resistant to both substances, the mortality rates of 68% and 72% for propoxur 0.1%, mosquitoes were found to be resistant to the substance in some areas, including the district municipality and outside the provincial municipality of Kalasin, Nong Khai provinces. In the municipality and Roi Et provincial municipality, and outside the municipality of Nong Bua Lam Phu province and Aedes in three areas of the Udon Thani and Loei provinces. There is a tendency for mosquito resistance to insecticides to increase and spread in more areas. Pothong et al. investigated the susceptibility of Aedes aegypti to chemicals in northern Thailand. The study found house mosquitoes ( Aedes aegypti). In Phitsanulok, Uttaradit, and Sukhothai provinces, in every implemented area, it can be seen that Aedes are resistant to two chemicals: alpha-cypermethrin 0.03% and lambda-cyhalothrin 0.03%. in every operation area, Aedes developed resistance against deltamethrin at 0.15% in almost all the operating sites. Except for Aedes aegypti in the Uttaradit district, Uttaradit province found that they were highly sensitive to deltamethrin 0.15%, Plernsub et al., ¹⁰ a susceptibility test of Aedes aegypti to chemical insecticides. Lopburi Phetchaburi, Prachinburi, Surat Thani, and Bangkok. The study found that Aedes are sensitive to chemicals in Pyrethroid and Organophosphate groups in the Lopburi province. Phetchaburi, Prachinburi, Surat Thani, and Bangkok are the most popular groups. The results from the susceptibility test of these substances in the area were moderate to high, especially the test with Deltamethrin 0.05% gave high sensitivity in most provinces. The mortality rate was 100, except in Surat Thani province, where the average mortality rate of Aedes aegypti was 81.6, meaning that the mosquitoes had begun to develop resistance to the chemical. and test results on the effectiveness of deltamethrin in eliminating edes. Deltamethrin adjuvant formulations in high-risk dengue fever districts had a better mortality effect than deltamethrin alone. In all areas, this corresponds to Stenhouse et al. on the susceptibility to chemicals and synergistic substances of Aedes aegypti in Thailand. ¹¹ This study found that Aedes aegypti in all regions had moderate to high resistance to pyrethroids. When studying chemicals together with synergistic substances, it was found that the mortality rate of Aedes aegypti in almost every area was higher than that in the empirical formulae. Most of the organophosphates were resistant to fenitrothion and perimorphs-methyl, and malathion resistance in all regions; Kongkaew et al. ¹² evaluated the efficiency of spraying chemicals to control mosquitoes of the local administration. The study found the efficiency of chemicals used as synthetic pyrethroids (deltamethrin, cypermethrin, and cyfluthrin). Testing the effectiveness of mixing chemicals in the ratio indicated by the label, it was found that all chemicals have a high level of effectiveness ^{13, 14} against mosquitoes, with mosquitoes having a mortality rate of 98.00%-100.00%. Kawada et al. ¹⁵ studied the effectiveness of Aedes aegypti repellent chemicals by semi-field fine spraying. The study showed the effectiveness of the chemical in eliminating house mosquitoes using four formulas: mixed formulae-1 (deltamethrin, S-bio-allethrin, piperonyl butoxide), mixed formulae-2 (lambda-cyhalothrin, tetramethrin, piperonyl butoxide), mixed formulae-3 (zeta cypermethrin, tetramethrin, piperonyl butoxide), and empirical formulae (cyfluthrin). According to the World Health Organization, using the combination rate indicated on the label and the highest combination rate. ¹⁶ The mixed formula-3 is the most effective in killing more than 90% of all four species of mosquitoes, while the mixed-1 and mixed-2 formulas at the combination rate indicated on the label are more than 90% effective in killing mosquitoes. Three strains (LS, CMS, TKS), but the empirical formula (cyfluthrin), when using the highest combination rate as recommended by the WHO, is effective against more than 90% of the mosquitoes in three strains (LS, CMS, TKS). However, when using the combination rate as indicated on the label to kill the mosquito, more than 90% of LS strains were effective, but less than 90% were effective in killing mosquitoes in all three species.

This study demonstrated that the combination of 0.5% deltamethrin, 0.75% S-bio-allethrin, and 10% piperonyl butoxide (DAP) was highly effective in eliminating Aedes aegypti in both indoor and outdoor environments. The study revealed that Aedes mosquitoes were susceptible to deltamethrin, and DAP proved significantly more effective than 0.5% deltamethrin in eradicating Aedes aegypti indoors and outdoors. The effectiveness of 0.5% deltamethrin in mosquito elimination was found to be higher indoors than outdoors. These findings are crucial for developing effective strategies to control the spread of dengue fever in high-risk areas. The use of DAP, in conjunction with other preventive measures, can substantially reduce the Aedes aegypti population and help prevent the spread of dengue fever. Further research is necessary to investigate the long-term effects of DAP and its environmental impact. Nonetheless, the results of this study offer valuable insights into the development of effective and sustainable strategies for controlling the spread of dengue fever in high-risk areas.

Ethics and consent not required for the performed study.