Spatiotemporal distribution of insecticide resistance in Anopheles culicifacies and Anopheles subpictus in Sri Lanka

Abstract

The malaria situation in Sri Lanka worsened during the 1990s with the emergence and spread of resistance to the drugs and insecticides used for control. Chloroquine resistance has increased rapidly over this period, but adverse changes in malaria transmission are more closely associated with insecticide use rather than drug resistance. Insecticide susceptibility tests were routinely carried out in key anopheline vectors across the country for more than a decade. These sentinel data were combined with data collected by other research programmes and used to map the spatial and temporal trends of insecticide resistance in the main vectors, Anopheles culicifacies and A. subpictus, and to examine the relationship between insecticide resistance, changes in national spraying regimens and malaria prevalence. Both species had widespread resistance to malathion, the insecticide of choice in the early 1990s. Both species were initially susceptible to the organophosphate and pyrethroid insecticides used operationally from 1993, but some resistance has now been selected. The levels of malathion and fenitrothion resistance in A. subpictus were higher in some ecological regions than others, which may be related to the distribution of sibling species, agricultural pesticide exposure and/or environmental factors. The study highlights that the emergence and spread of insecticide resistance is a constant threat and that active surveillance systems are vital in identifying key vectors and evidence of resistance.

The dominant Anopheles vectors of human malaria in the Asia-Pacific region: occurrence data, distribution maps and bionomic précis

“…The Subpictus Complex has a wide distribution, ranging from northeastern Pakistan, across India, Sri Lanka, Bangladesh, Myanmar, Thailand and along coastal regions of southern Cambodia, Vietnam and coastal areas of Malaysia, Indonesia, Timor-Leste, Papua New Guinea and extending as far east as the Solomon Islands [67,154,174,181,329,345,451,452,455-473]. Species identification has not been widely reported and therefore informally named members of the complex are only known from limited areas of India, Sri Lanka, the Philippines and Thailand [451,452,471,474,475].…”

“…MALVECASIA [65,66]) and a number of recent publications (e.g. [23,67-77]) provide detailed information that should be considered alongside this current work.…”

Nigeria Anopheles Vector Database: An Overview of 100 Years' Research

“…gambiae s.s. to permethrin and DDT, which is of major concern given that this vector was found to have among the highest malaria sporozoite and LF microfilaria rates in Nigeria, permethrin is currently the only class of insecticide used for ITNs, and permethrin and DDT are widely used for IRS [10]. Vector control can be hampered by the occurrence of insecticide resistance and as such monitoring of insecticide resistance regularly across a wide geographical area is critical [7], [11], [12], [129]–[132]. The findings also highlight the importance of a consensus standardization of the number and location of surveillance sites and the frequency with which resistance monitoring should occur [11].…”

Malaria in São Tomé and Principe: On the Brink of Elimination after Three Years of Effective Antimalarial Measures

“…In Sri Lanka, widespread insecticide resistance in the main Anopheles vectors might have been the main reason for the resurgence of malaria after many years of IRS program with the same insecticide. 37 Thus, monitoring of insecticide resistance, which is a constant threat, is critical in informing the program to take appropriate measures. The country should establish a link with experts and centers of excellence for the management of insecticide resistance.…”