Malaria risk and receptivity: Continuing development of insecticide resistance in the major malaria vector Anopheles arabiensis in northern KwaZulu-Natal, South Africa

Abstract

Malaria incidence in South Africa is highest in the three endemic provinces: KwaZulu-Natal, Mpumalanga and Limpopo. The contribution to malaria transmission by several mosquito species, variation in their resting behaviours and low levels of insecticide resistance makes it necessary to periodically monitor Anopheles species assemblages and resistance phenotypes in vector populations. The aim of this study was therefore to assess Anopheles species assemblage in northern KwaZulu-Natal and to collect insecticide susceptibility data for An. arabiensis, the primary vector of malaria in that province. Anopheles specimens were collected from Mamfene, Jozini, northern KwaZulu-Natal from November 2019 to April 2021. Progeny of wild-collected An. arabiensis females were used for standard insecticide susceptibility tests and synergist bioassays. Anopheles arabiensis contributed 85.6% (n=11 062) of the total catches. Samples for subsequent insecticide susceptibility bioassays were selected from 212 An. arabiensis families. These showed low-level resistance to DDT, permethrin, deltamethrin, and bendiocarb, as well as full susceptibility to pirimiphos-methyl. Synergist bioassays using piperonyl butoxide and triphenyl phosphate suggest oxygenase-based pyrethroid and esterase-mediated sequestration of bendiocarb. These low levels of resistance are unlikely to be operationally significant at present. It is concluded that northern KwaZulu-Natal Province remains receptive to malaria transmission despite ongoing control and elimination interventions. This is due to the perennial presence of the major vector An. arabiensis and other secondary vector species. The continued detection of low-frequency insecticide resistance phenotypes in An. arabiensis is cause for concern and requires periodic monitoring for changes in resistance frequency and intensity.

Generation of specific immune memory by bacterial exposure in the major malaria vector Anopheles arabiensis (Diptera: Culicidae)

“…Although these experiments need to be confirmed with wild mosquitoes, it is worth noting that the population used to test the generation of memory in the F1s have basal DDT and pyrethroid resistance ( Munhenga et al ., 2022 ). Although there is not a wild comparison for the generation of memory in insecticide susceptible and resistant populations, the findings of this study still have value.…”

“…This was the same case for the wild population tested. The population tested does have low-level insecticide resistance ( Munhenga et al ., 2022 ). Again, this suggests a role for insecticide resistance in the generation of memory.…”

The Malaria Burden: A South African Perspective

“…In 2000, when the frst-line malaria drug sulphadoxinepyrimethamine failed in South Africa, they reintroduced dichlorodiphenyltrichloroethane (DDT) for traditional structures while maintaining pyrethroids for modernised housing, using a mosaic strategy for resistance management [16,17]. Artemisinin-containing combination treatment (ACT) was also introduced for malaria treatment [17,18].…”

Field evaluation of the residual efficacy of new generation insecticides for potential use in indoor residual spray programmes in South Africa

“…In the southern African region, resistance to pyrethroids and DDT has been reported [ 10 , 11 ]. Previously, pockets of resistance to most classes of insecticides were reported from especially KwaZulu-Natal [ 12 ] and it was recommended that insecticide resistance management as well as alternative control techniques be implemented to target outdoor-resting An. arabiensis in northern KwaZulu-Natal.…”