Long-lasting microbial larvicides for controlling insecticide resistant and outdoor transmitting vectors: a cost-effective supplement for malaria interventions

Abstract

The issues of pyrethroid resistance and outdoor malaria parasite transmission have prompted the WHO to call for the development and adoption of viable alternative vector control methods. Larval source management is one of the core malaria vector interventions recommended by the Ministry of Health in many African countries, but it is rarely implemented due to concerns on its cost-effectiveness. New long-lasting microbial larvicide can be a promising cost-effective supplement to current vector control and elimination methods because microbial larvicide uses killing mechanisms different from pyrethroids and other chemical insecticides. It has been shown to be effective in reducing the overall vector abundance and thus both indoor and outdoor transmission. In our opinion, the long-lasting formulation can potentially reduce the cost of larvicide field application, and should be evaluated for its cost-effectiveness, resistance development, and impact on non-target organisms when integrating with other malaria vector control measures. In this opinion, we highlight that long-lasting microbial larvicide can be a potential cost-effective product that complements current front-line long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS) programs for malaria control and elimination. Microbial larviciding targets immature mosquitoes, reduces both indoor and outdoor transmission and is not affected by vector resistance to synthetic insecticides. This control method is a shift from the conventional LLINs and IRS programs that mainly target indoor-biting and resting adult mosquitoes.

Bacterial Toxins Active against Mosquitoes: Mode of Action and Resistance

“…gambiae [301]; and in Senegal against Anopheles arabiensis [302]. These combined larvicides are viable options for controlling mosquito populations and interrupting disease transmission, along with other measures [4,[294][295][296]303,304].…”

“…The successful experiences of using Bti in combination with L. sphaericus led to the development of commercial combined products containing crystals of both bacteria. Some of them are long-lasting microbial larvicides whose formulations provide a slow release of the active ingredients over 90 to 180 days [ 294 , 295 , 296 ], and they have been used to control mosquito larvae in a variety of landscapes and purposes ( Table 1 ). In urban areas, such larvicides have been used in several countries, such as in Italy, Switzerland, and Spain to control Ae.…”

Larval mosquito management and risk to aquatic ecosystems: A comparative approach including current tactics and gene-drive Anopheles techniques

“…For the past 20 years, malaria in much of sub-Saharan Africa has primarily been managed by indoor residual treatments of insecticides, long-lasting insecticidal bednets, and artemisinin-based combination therapy (WHO 2020 ; Zhou et al 2020 ). Although these tactics have been remarkably successful in lowering malaria deaths, these gains are threatened by resistance, persistence, and resurgence.…”

Monthly biological larviciding associated with a tenfold decrease in larval density in fish farming ponds and reduced community-wide malaria incidence in northwestern Brazil

“…Importantly, larviciding may be more effective to suppress outdoor biting and resting mosquitoes, such as the primary Amazonian malaria vector An. darlingi [ 2 , 17 ], than core vector control interventions that target endophilic and endophagic anophelines, such as LLIN distribution and IRS [ 30 ].…”

“…This cRDT, included in a recent systematic Cochrane review [ 27 ], found a nearly fivefold decrease in malaria incidence in intervention villages (5 cases per 100 person-years) compared with control villages (23 cases per 100 person-years). Larviciding is rarely assessed using cRCTs, in part because of the high cost and the complex logistics of these studies, with substantial risk of intervention spill-over affecting nearby control communities [ 30 ]. Conversely, ITSA with comparison group(s) has been increasingly used to measure the effectiveness of community interventions [ 32 , 33 ] and may provide a cost-effective alternative to cRCTs in the evaluation of larviciding and other malaria control interventions.…”