Research Article: Insecticide resistance in Aedes aegypti: An impact from human urbanization?

Date Published: June 24, 2019

Publisher: Public Library of Science

Author(s): Tri Baskoro Tunggul Satoto, Hary Satrisno, Lutfan Lazuardi, Ajib Diptyanusa, Abdallah M. Samy.

http://doi.org/10.1371/journal.pone.0218079

Abstract

In the city of Magelang, Indonesia, the distribution of Dengue Haemorhagic Fever (DHF) cases tend to be clustered, ever changing along with human urbanization from 2014 to 2017. Although DHF cases have been less reported in the city of Magelang for the past 5 years, vector control measures by using insecticide space spraying, particularly permethrin, have been continuously performed. Current study aimed to detect kdr mutations associated with pyrethroid resistance in Ae. aegypti and to study possible association between insecticide resistance and DHF case distribution related to human urbanization. The study was a cross sectional study conducted in 3 sub-districts in the city of Magelang, Central Java, Indonesia. Eggs of Ae. aegypti collected from 195 sample households were reared and were tested for resistance to pyrethroids by using PCR. Primers AaSCF1 and AaSCR4, and primers AaSCF7 and AaSCR7 were used in detecting presence of mutation in VGSC IIS6 and IIIS6 gene, respectively. Fragments of amplified DNA were sequenced and were analyzed. Spatio-temporal using Standard Deviational Ellipse (SDE) was performed to obtain mapping of DHF case distribution trends. The total number of DHF case was 380 cases, with the most cases (158) occurred in 2015 and the least cases (66) reported in 2017. DHF case distribution was grouped into several clusters. SDE calculation demonstrated movement of DHF case in the direction to principal arterial road, suggesting link to urbanization. Gene sequencing demonstrated VGSC IIS6 gene mutation (S989P and V1016G) in Ae. aegypti collected from study areas, indicating resistance to permethrin. VGSC IIIS6 gene mutation was not found. Current study concluded that multiple kdr mutations associated with resistance to pyrethroid was detected in Ae. aegypti, and that human urbanization may have a role in the development of such resistance.

Partial Text

Dengue is one of the fastest growing viral mosquito-borne diseases affecting tropical and subtropical regions in the world, including Indonesia [1]. The disease is caused by dengue virus principally transmitted by Aedes aegypti [2]. Roughly two-fifth of global population live in high-risk areas for dengue transmission [3], with an estimation of 3.9 billion people are at risk of infection with dengue viruses [4]. The number of dengue cases has been increasing over the last five years with recurring epidemics, particularly in Indonesia, Thailand, and Myanmar [5]. Recent report by the Ministry of Health of Republic of Indonesia showed a total of 129,650 dengue cases in 2015, with case fatality rate (CFR) of 0.97% [6]. This was generally due to increases in vector density, and human population size and mobilization [7].

In total, the number of reported DHF cases in study areas from 2014 through 2017 was 380 cases: 69 cases reported in 2014, 158 cases reported in 2015, 87 cases reported in 2016, and 66 cases reported in 2017. The IR per 100,000 population was observed highest in 2015 (Table 1). Two death cases were reported in 2015 and 4 death cases were reported in 2016. Table 1 also demonstrated population density along the years from 2014 through 2017. Population increase in general was subtle, however, the trend was observed highest in Central Magelang sub-district, showing tendency of human urbanization into city center. The distribution of DHF cases demonstrated a clustered pattern further divided into primary and secondary clusters (Fig 1).

The city of Magelang, located in the middle of Magelang Regency, is a city in Central Java that is routinely affected by DHF. The city contributes 1.67% of Magelang Regency with 18.12 km2 of areas. The city is a fertile agricultural area and one of the most densely populated area in Central Java, with population density of 6,693/km2. As of 2017, population in the city of Magelang was 121,293 people, distributed in 3 sub-districts: North (36,445), Central (44,144), and South Magelang (40,704). Current study results showed the highest number of reported DHF case in 2015, along with the highest IR per 100,000 population. In the city of Magelang, permethrin was newly introduced in 2014 after prolonged use of malathion in space spraying. In Magelang, mosquitoes have been known to be resistant to malathion, as demonstrated by mosquito mortality of <50% throughout the city [19]. Since insecticide resistance to malathion was increased drastically in 2013 [MOH of Republic of Indonesia, 2017, unpublished], local government started using permethrin in insecticide space spraying in 2014 to reduce Ae. aegypti population as main vectors of DHF. The number of reported DHF case was decreased significantly after introduction of permethrin. However, the number of DHF case showed dramatic increase in 2015. This may be due to several reasons: increased mosquito population, human movement, increasing trades, or insecticide resistance [7, 32]. Furthermore, DHF incidence decreased after year 2015 most likely because local government was concerned by drastic increase of DHF incidence that programs involving source reduction and environmental management were intensified in the community ever since [8]. The use of permethrin in the city of Magelang, Central Java, Indonesia has been routinely applied in vector control since 2014 after decades of malathion use. Current study demonstrated multiple kdr mutations linked with pyrethroid resistance in Ae. aegypti mosquitoes collected from the city of Magelang, as evidenced by the presence of VGSC IIS6 gene mutation (S989P and V1016G). In the city of Magelang, development of insecticide resistance may be potentially be related to slight increase in population size and human urbanization.   Source: http://doi.org/10.1371/journal.pone.0218079