Susceptibility to common insecticides and detoxifying enzyme activities in Anopheles sundaicus (sensu lato) after cessation of indoor residual spraying of insecticides in the Jaffna Peninsula and its surroundings in northern Sri Lanka

Abstract

BackgroundSri Lanka has been malaria-free since 2013 but re-introduction of malaria transmission by infected overseas travelers is possible due to a prevalence of potent malaria vectors. Knowledge of the insecticide resistance status among Anopheles vectors is important if vector control has to be reintroduced in the island. The present study investigated the insecticide susceptibility levels and resistance mechanisms of Anopheles sundaicus (sensu lato) (previously classified as Anopheles subpictus species B) an important malaria vector in the Jaffna Peninsula and it surroundings in northern Sri Lanka after indoor residual spraying of insecticides was terminated in 2013.ResultsSpecies-specific PCR assays identified An. sundaicus (s.l.) in four locations in the Jaffna and adjacent Kilinochchi districts. Bioassays confirmed that An. sundaicus (s.l.) collected in Kilinochchi were completely susceptible to 0.05% deltamethrin and 5% malathion and resistant to 4% dichlorodiphenyltrichloroethane (DDT), whereas those from Jaffna were relatively susceptible to all three insecticides. Kilinochchi populations of An. sundaicus (s.l.) showed significantly higher glutathione S-transferase activity than population from Jaffna. However, Jaffna An. sundaicus (s.l.) had significantly higher Propoxur-resistant acetylcholinesterase activity. Activities of non-specific esterases and monooxygenases were not significantly elevated in An. sundaicus (s.l.) collected in both districts.ConclusionsThe susceptibility to malathion and deltamethrin in An. sundaicus (s.l.) suggests that they can be still used for controlling this potential malaria vector in the Jaffna Peninsula and adjacent areas. Continuing country-wide studies on other malaria vectors and their insecticide susceptibilities are important in this regard.

Anopheline bionomics, insecticide resistance and transnational dispersion in the context of controlling a possible recurrence of malaria transmission in Jaffna city in northern Sri Lanka

“…The four anopheline species collected in Jaffna city were resistant to DDT despite the cessation of DDT use for indoor residual spraying (IRS) in Jaffna in early 1970s. Resistance to DDT declined slowly after cessation of use, but increased again after 1983 due to a glutathione-S transferase-based mechanism, postulated to be initially caused by DDT and subsequently by exposure to the malathion used for IRS and other organophosphates used for controlling agricultural pests [2,27,45,46]. The results confirm that An.…”

“…stephensi in Jaffna was resistant to DDT and deltamethrin [15], we now show that there are no mutations in the sequenced IIS6 segment of the VGSC protein in this mosquito. Resistance may, therefore, be caused by other mechanisms such as increased activities of detoxifying enzymes [27,45,46] and this merits further investigation.…”

Molecular forms of the Indian Anopheles subpictus complex differ in their susceptibility to insecticides and the presence of knockdown resistance (kdr) mutations in the voltage-gated sodium channel

“…This study reports contrasting differences in insecticide resistance among two molecular forms of the Subpictus Complex and the occurrence of kdr mutations that confer resistance against DDT and pyrethroids. These two molecular forms are highly diverged to the extent that Form B is phylogenetically closer to the sundaicus complex; thus various authors [ 10 , 12 – 13 ] have considered Form B as a member of the sundaicus complex. Therefore, it is important to identify the correct biological species for the effective management of vectors.…”

“…Phylogenetic studies based on ITS2, 28S-rDNA and mtDNA revealed that Form B is closely related to members of the Sundaicus Complex and is far distantly related to Form A. Surendran et al [ 12 ] and Sindhania et al [ 10 ], therefore recommended classifying species B as molecular form B under the Sundaicus Complex. Moreover, Sivabalakrishnan et al [ 13 ] have described species B as An . sundaicus s .…”

Measuring differences between phenomenological growth models applied to epidemiology

“…We herein focus on phenomenological growth models (PGMs) that only require a small number of parameters are commonly used to describe epidemic growth patterns, and which can be expressed by an ordinary differential equation (ODE) of the type where is time, is the total size of the epidemic (the cumulative number of cases) at time , is the initial number of cases, is an incidence function that is specific to each PGM under study, and is a vector of parameters. Such models have been used to study the epidemics of influenza [16] , [17] , [18] , Ebola [19] , [20] , [21] , [22] , Zika [23] , [24] , [25] , Chikungunya [26] , and others of global interest. The current COVID-19 pandemic is a scenario for which such models are of obvious importance [27] , [28] , [29] , [30] , [31] , [32] , [33] , [34] .…”