Wide area spray of bacterial larvicide,Bacillus thuringiensis israelensisstrain AM65-52, integrated in the national vector control program impacts dengue transmission in an urban township in Sibu district, Sarawak, Malaysia.

Rezal Bohari,Chong Jin Hin,Teoh Guat Ney,Muhamad Rais Abdullah,Lee Han Lim,Asmad Matusop,Seleena Benjamin,Richard Paul

doi:10.1371/journal.pone.0230910

Rezal Bohari, Chong Jin Hin + Show 6 more

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https://doi.org/10.1371/journal.pone.0230910

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Abstract

Several sites, Z-7L, Z-5 and Z-14, in Sibu district, Sarawak, Malaysia, experienced intense dengue transmission in 2014 that continued into 2015. A pilot study with Bacillus thuringiensis israelensis (Bti) to control Aedes aegypti (L.) and Ae. albopictus (Skuse) was evaluated in Z-7L, a densely populated site of 12 ha. Bti treatments were conducted weekly from epidemiology week (EW) 24/2015 for 4 weeks, followed by fortnight treatments for 2 months, in addition to the routine control activities. Bti was directly introduced into potable containers and the outdoor artificial and natural containers were treated via a wide area spray application method using a backpack mister. Aedes indices significantly reduced during the treatment and post treatment phases, compared to the control site, Z-5 (p<0.05). A 51 fold reduction in the incidence rate per 100,000 population (IR) was observed, with one case in 25 weeks (EW 29–52). In Z-5 and Z-14, control sites, a 6 fold reduction in the IR was observed from EW 29–52. However, almost every week there were dengue cases in Z-14 and until EW 44 in Z-5. In 2016, dengue cases resurfaced in Z-7L from EW 4. Intensive routine control activities were conducted, but the IR continued to escalate. The wide area Bti spray misting of the outdoor containers was then included from EW 27 on fortnight intervals. A 6 fold reduction in IR was observed in the Bti treatment phase (EW 32–52) with no successive weekly cases after EW 37. However, in the control sites, there were dengue cases throughout the year from EW 1–52, particularly in Z-14. We feel that the wide area Bti spray application method is an integral component in the control program, in conjunction with other control measures carried out, to suppress the vector population in outdoor cryptic containers and to interrupt the disease transmission.

Highlights

Dengue is one of the serious and major public health mosquito borne diseases throughout tropical and sub-tropical regions of the world, including Malaysia
For the pilot study we focused in Zone 5 (Z-5), Zone 7 (Z-7) and Zone 14 (Z-14)
The larval mortality was observed in all the containers within 3–5 hours of exposure to the sprayed Bacillus thuringiensis israelensis (Bti) droplets, irrespective of the location of the test containers, whether from dense undergrowth or from the upper levels of the premise

Summary

Introduction

Dengue is one of the serious and major public health mosquito borne diseases throughout tropical and sub-tropical regions of the world, including Malaysia. In Malaysia, since the year 2000, the number of dengue cases and number of deaths have increased, on average by 14% and 8% per year, respectively [1]. Changes in the circulating dengue virus serotype in the community have led to an increase of dengue cases and deaths [2]. In Malaysia, the two dengue vectors are Aedes aegypti (L.) and Ae. albopictus (Skuse) [3]. They breed indoors and outdoors, with Ae. aegypti being a dominant indoor breeder and Ae. albopictus as the dominant outdoor breeder and they have an ability to colonize in varied type of artificial and natural containers [4,5,6]

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