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.
Highlights
Challenges in the role of larval mosquito control Effectiveness of larviciding Larval control and environmental management have played prominent roles in malaria elimination in the past [28, 29]
Microcosm test to determine the effective duration in An. gambiae larval killing; b Testing the effectiveness of the long-lasting larvicide using a cohort of larval habitats
Results indicated that long-lasting microbial larvicides (LLML) reduced malaria vector pupal productivity by 100% in the first two months and by 63.4%–90.2% for 3–5 months after application (Fig. 1b)
Summary
There has been a massive scale-up of antimalarial interventions since 2000 including long-lasting insecticidal nets (LLINs), indoor residual spraying (IRS), and artemisinin-based combination therapy (ACT). A number of recent studies have documented changes in the biting behaviour of An. gambiae and An. funestus, from biting exclusively indoors at night to biting both indoors and outdoors during early evening and morning hours when people are not protected by IRS or LLINs, or biting indoors but resting outdoors [7, 8] These behavioural changes in the mosquitoes have unquestionably challenged the effectiveness of existing control programs that primarily target indoor mosquitoes and urged the need of an expanded or alternative vector control toolkit. Bacillus thuringiensis israelensis (Bti) and Bacillus sphaericus (Bs) based bacterial agents are considered as highly effective microbial mosquito larvicide, which targets aquatic stages and reduces both indoor and outdoor mosquitoes They can be used either individually or as a mixture, and have been shown to be safe to non-target organisms cohabiting with the mosquito larvae in the natural environment [27]. Further investigations on their efficacy and cost-effectiveness are still underway
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