In the past decade, the massive scale-up of insecticide-treated bed nets (ITNs) and indoor residual spraying (IRS), together with the use of artemisinin-based combination treatments, have led to major changes in malaria epidemiology and vector biology. Overall malaria prevalence and incidence have been greatly reduced worldwide [
1]. But the reductions in malaria have not been achieved uniformly; some sites have experienced continued reductions in both clinical malaria and overall parasite prevalence [
2‐
6], while other sites showed stability or resurgence in malaria despite high coverage of ITNs and IRS [
7‐
12]. Persistence and resurgence of vector populations continues to be an important issue for malaria control and elimination [
12‐
16]. More importantly, extensive use of ITNs and IRS has created intensive selection pressures for malaria vector insecticide resistance as well as for potential outdoor transmission, which appears to be limiting the success of ITNs and IRS. For example, in Africa, where malaria is most prevalent and pyrethroid-impregnated ITNs have been used for more than a decade, there is ample evidence of the emergence and spread of pyrethroid resistance in
Anopheles gambiae s.s., the major African malaria vector, as well as in
An. arabiensis and
An. funestus s.l. [
17‐
20]. Both the prevalence of
An. gambiae s.s. resistance to pyrethroids and DDT and the frequency of knock-down resistance (
kdr) have reached alarming levels throughout Africa from 2010–2012 [
18]. Unfortunately, pyrethroids are the only class of insecticides that the World Health Organization (WHO) recommends for the treatment of ITNs [
21]. Furthermore, a number of recent studies have documented a shift in the biting behavior of
An. gambiae s.s. and
An. funestus, from biting exclusively indoors at night to biting both indoors and outdoors during early evening and morning hours when people are active but not protected by IRS or ITNs, or to biting indoors but resting outdoors [
22‐
24]. Apart from these intraspecific changes in biting behavior, shifts in vector species composition, i.e., from the previously predominant indoor-biting
An. gambiae s.s. to the concurrently predominant species
An. arabiensis, which prefers to bite and rest outdoors in some parts of Africa, can also increase outdoor transmission [
25‐
28]. Because IRS and ITNs have little impact on outdoor-resting and outdoor- and early-biting vectors, outdoor transmission represents one of the most important challenges in malaria control. New interventions are urgently needed to augment current public health measures and reduce outdoor transmission [
29].
Larval control has historically been very successful and is widely used for mosquito control in many parts of the developed world [
30‐
33], but is not commonly used in Africa. Field evaluation of anopheline mosquitoes in Africa found that larviciding was effective in killing anopheline larvae and reducing adult malaria vector abundance in various sites [
34‐
39]. Microbial larvicides are effective in controlling malaria vectors, and they can be used on a large scale in combination with ongoing ITN and IRS programs [
35,
38,
40]. However, conventional larvicide formulations are associated with high material and operational costs due to the need for frequent habitat re-treatment, i.e., weekly re-treatment, as well as logistical issues in the field [
34‐
36,
40,
41]. Recently, an improved slow-release larvicide formulation was field-tested for controlling
Anopheles mosquitoes, yielding an effective duration of approximately 4 weeks [
42]. Considering the monthly reapplication interval, this still may not be a cost-effective product for large-scale application. The new US EPA-approved long-lasting formulation, FourStar Microbial Briquets (Central Life Sciences, Sag Harbor, NY, USA), is potentially effective for up to 6 months (
http://www.centralmosquitocontrol.com/all-products/fourstar/fourstar-briquet-180), and preliminary data suggest that it is effective in malaria mosquito control [GZ, unpublished data]. Field-testing is needed to determine the efficacy and cost-effectiveness of this long-lasting larvicide.
The central objective of this study is to determine the effectiveness and cost-effectiveness of long-lasting microbial larviciding (LLML) on the incidence of clinical malaria and the reduction of transmission intensity. The hypothesis is that adding LLML to ongoing ITN and IRS programs will lead to significant reductions in both indoor and outdoor malaria transmission and malaria incidence as well as cost savings. This paper describes a protocol for evaluating the impact of LLML in reducing malaria vector populations and clinical malaria incidence.