Evaluation of DawaPlus 3.0 and DawaPlus 4.0, deltamethrin–PBO combination nets against pyrethroid-resistant Anopheles culicifacies in experimental huts in India

Abstract

Background: The development of resistance in vectors is one of the major impediments for malaria control. Adding synergists to insecticides has proven to be an alternative choice for controlling resistant mosquitoes. DawaPlus 3.0 and DawaPlus 4.0 are new long-lasting insecticidal nets (LLINs) in which deltamethrin and a synergist, piperonyl butoxide (PBO) are added into filaments and their efficacy was tested against resistant malaria vector, Anopheles culicifacies in experimental huts in India. Methods: The performance of two trial nets in terms of deterrence induced exiting, blood-feeding inhibition and mortality of An. culicifacies was compared with DawaPlus 2.0 and untreated net. Results: There was a significant reduction in entry, blood feeding and mortality (p < 0.05) and increase in exit rates of An. culicifacies in the treatment arms compared to untreated arm. But, both candidate LNs washed 20 times could not perform better than the washed reference net (DawaPlus 2.0). Cone bioassay results showed that all the treatment arms (both washed and unwashed) produced < 80% mortality of An. culicifacies before and after hut evaluation. Conclusions: DawaPlus 3.0 and DawaPlus 4.0 with their current specification may not be as effective as required to control the resistant vector, An. culicifacies, in east-central India.

Emerging mosquito resistance to piperonyl butoxide-synergized pyrethroid insecticide and its mechanism

“…The chief reason for producing PBO-LLIN is the widespread high pyrethroid resistance levels in Anopheles mosquitoes in malaria-endemic African countries. Although the majority of previous studies found that PBO-LLIN outperformed LLIN at increasing killing power and/or reducing malaria infections [21–23,55], several studies reported reduced efficacy of PBO-LLIN against highly resistant Anopheles and Culex mosquitoes [28,30,49,53–55]. We should note that it is unlikely that African Anopheles mosquitoes were exposed to PBO or PBO-synergized insecticide products before large-scale rollout of PBO-LLINs.…”

“…A recent study in Mozambique found that highly insecticide-resistant Anopheles funestus was also resistant to PBO-LLIN [28]. A number of other studies also found that pre-treatment of insecticide-resistant Aedes, Anopheles and Culex mosquitoes did not fully restore the mosquitoes' susceptibility to insecticides and sometimes had a very limited effect on mortality [29][30][31]. There are several possible causes for mosquito to tolerant PBO-synergized insecticides, including: A) the PBO concentration is too low or the exposure duration is too short; B) the resistance is so intense that PBO exposure cannot .…”

Efficacy evaluation of Veeralin LN, a PBO-incorporated alpha-cypermethrin long-lasting insecticidal net against Anopheles culicifacies in experimental huts in Odisha State

“…An experimental hut study conducted recently in the same area showed that the exit rate (induced exophily) of An. culicifacies in the untreated arm was 23.9% [ 19 ]. However, a higher exophily (40.5–57.5%) was recorded with the treated arms, but between them, there was no significant difference.…”

“…Experimental hut studies conducted in West and Central Africa, Tanzania and Togo with high pyrethroid resistance showed that pyrethroid-PBO nets performed better than standard-LLINs [ 9 , 10 , 25 ], whereas in moderate to low pyrethroid resistant areas, there was little or no difference in the effect of unwashed/washed pyrethroid-PBO nets compared to unwashed/washed standard-LLINs [ 19 , 25 ]. This may be due to the wide variation in insecticide resistance levels in malaria vector species.…”