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.

Insecticide resistance and molecular characterization of knockdown resistance (kdr) in Culex quinquefasciatus mosquitoes in Sri Lanka.

Resistance to pyrethroids (PY) and organophosphate (OP) insecticides is widespread among populations of Culex quinquefasciatus, the major vector of lymphatic filariasis (LF). The present study was designed to detect the L1014F kdr (knockdown resistant) mutation among Cx. quinquefasciatus populations in the filarial belt of Sri Lanka. Mosquitoes were reared from field-caught larvae from seven localities where LF is endemic. Susceptibility status of Cx. quinquefasciatus to adulticides, 0.05% deltamethrin, 0.75% permethrin, 5% malathion, and the larvicide temephos was determined using the standard WHO susceptibility tests. A fragment of vgsc gene was amplified and sequenced to identify the responsible kdr mutations. The susceptibility test results revealed less than 90% mortalities for 0.05% deltamethrin, and 0.75% permethrin and temephos. For 5% malathion, all study sites except Maharagama revealed greater than 90% mortality. The L1014F kdr mutation was observed in all studied populations. Although the overall microfilaria rate is less than 1% in the country, there is a high risk of re-emergence of LF in Sri Lanka due to abundant Cx. quinquefasciatus mosquitoes, increased resistant status to currently used insecticides, imported LF cases, higher rates of microfilaria among neighboring countries, and the advancement of tourism.

First report of V1016G and S989P knockdown resistant (kdr) mutations in pyrethroid-resistant Sri Lankan Aedes aegypti mosquitoes.

BACKGROUND: Dengue is a serious arboviral disease in Sri Lanka with a large number of dengue fever (DF) cases every year. Control of the primary vector Aedes aegypti depends upon larval habitat source reduction and insecticide application. However, increases in the number of reported cases suggest the inefficiency of current control strategies and the possibility of resistance to currently used insecticides. Early detection of mutations in the voltage-gated sodium channel (vgsc) gene that confer knockdown resistance (kdr) to pyrethroid insecticides is important in resistance management in vector populations. RESULTS: Resistance to pyrethroid insecticides was detected in the three populations studied. Polymerase chain reaction was used to detect the presence of two kdr mutations F1534C and V1016G. During this process a S989P mutation was also detected in pyrethroid-resistant Ae. aegypti populations. These mutations were found to be widespread and frequent in the collections studied. CONCLUSIONS: To our knowledge, this study reveals for the first time the presence of V1016G and S989P mutant alleles in the vgsc of Sri Lankan Ae. aegypti populations. The spread of the mutant alleles throughout the country poses a threat of increased resistance to pyrethroids. Long-term insecticide applications and indiscriminate use of pyrethroids has led to the evolution of resistance. More strategic and diverse strategies, including novel insecticides with new modes of action and community participation, should be engaged for Ae. aegypti control.