Review of insecticide resistance and behavioral avoidance of vectors of human diseases in Thailand

Abstract

Physiological resistance and behavioral responses of mosquito vectors to insecticides are critical aspects of the chemical-based disease control equation. The complex interaction between lethal, sub-lethal and excitation/repellent ('excito-repellent’) properties of chemicals is typically overlooked in vector management and control programs. The development of “physiological” resistance, metabolic and/or target site modifications, to insecticides has been well documented in many insect groups and disease vectors around the world. In Thailand, resistance in many mosquito populations has developed to all three classes of insecticidal active ingredients currently used for vector control with a majority being synthetic-derived pyrethroids. Evidence of low-grade insecticide resistance requires immediate countermeasures to mitigate further intensification and spread of the genetic mechanisms responsible for resistance. This can take the form of rotation of a different class of chemical, addition of a synergist, mixtures of chemicals or concurrent mosaic application of different classes of chemicals. From the gathered evidence, the distribution and degree of physiological resistance has been restricted in specific areas of Thailand in spite of long-term use of chemicals to control insect pests and disease vectors throughout the country. Most surprisingly, there have been no reported cases of pyrethroid resistance in anopheline populations in the country from 2000 to 2011. The precise reasons for this are unclear but we assume that behavioral avoidance to insecticides may play a significant role in reducing the selection pressure and thus occurrence and spread of insecticide resistance. The review herein provides information regarding the status of physiological resistance and behavioral avoidance of the primary mosquito vectors of human diseases to insecticides in Thailand from 2000 to 2011.

Insecticides resistance in the Culex quinquefasciatus populations from northern Thailand and possible resistance mechanisms

“…quinquefasciatus is a potential vector of the filarial worm Wuchereria bancrofti, the agent of bancroftian filariasis, in urban areas [1][2][3]. In Thailand, the number of migrant workers from endemic countries, as well as from hill tribes along the Thai-Myanmar border has been increasing in recent years [4]. Some of them carry W. bancrofti microfilariae without noticeable symptoms [5,6].…”

“…Disease control and prevention efforts involve vector control by insecticide application, space spraying with deltamethrin, is the most common method for controlling outbreaks of mosquito borne diseases in Thailand [4]. However, the heavy and long-term use of insecticides in public health and agriculture has led to the development of insecticide resistance [7,8].…”

“…Resistance to DDT and pyrethroids has been documented in populations of Cx. quinquefasciatus in Thailand and many other countries [4,[9][10][11][12][13], but little is known about the resistance mechanism of this vector in Thailand.…”

A Note on the Insecticide Susceptibility Status of Disease Vectors; Anopheles sundaicus and Aedes albopictus, in the Car Nicobar Island

“…In Thailand, DDT for the control of dengue vector had led to the development of resistance to this insecticide, in a short period of two years [19]. Kdr mutation of voltage-gated sodium channel may be responsible for the resistance to DDT, in addition to the detoxifying enzyme activity [20]. Resistance to fenitrothion for Ae.…”

Repellents and New “Spaces of Concern” in Global Health

“…Pyrethroids-long-lasting chemicals that are highly toxic to insects but generally harmless to birds, humans, and other mammals-proved a highly effective front-line defense when applied to bed nets and have since been held responsible for the prevention of millions of malaria-related deaths (Greenwood 2008). That efficacy has sadly also proven finite: after almost twenty years using the same class of insecticides in the same way, mosquitoes are becoming increasingly resistant to pyrethroids throughout sub-Saharan Africa, Southeast Asia and elsewhere (Ranson et al 2011;Chareonviriyaphap et al 2013).…”