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

PLoS One. 2020 Apr 1;15(4):e0230910. doi: 10.1371/journal.pone.0230910. eCollection 2020.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aedes / microbiology
  • Aedes / virology
  • Animals
  • Bacillus thuringiensis*
  • Biological Control Agents*
  • Dengue* / epidemiology
  • Dengue* / transmission
  • Disease Reservoirs / virology
  • Disease Vectors
  • Insecticides
  • Larva / microbiology
  • Larva / virology
  • Malaysia / epidemiology
  • Mosquito Control / methods
  • Mosquito Vectors* / microbiology
  • Mosquito Vectors* / virology
  • Pilot Projects
  • Prevalence

Substances

  • Biological Control Agents
  • Insecticides

Grants and funding

The study was mainly funded by the Ministry of Health (MOH), Malaysia, in the form of authors’ and staff salaries and travel expenses for field activities where relevant, except for one of the authors, Seleena Benjamin, whose salary and related expenses were supported by Valent BioSciences LLC (VBC). The field-laboratory equipment and materials for the study were supplied by the MOH Malaysia. The product, VectoBac WG, was purchased by the MOH Malaysia for the control of mosquito larvae and supplied to all the States in Malaysia. However, during the pilot project in 2015, VBC supported the supply of 3 back pack sprayers and the VectoBac WG product. In 2016 and after the product is from the MOH, Malaysia. The execution of the field work and collection of data were conducted by the MOH Malaysia staff who are from the Divisional Health Office, Sibu and the State Health Department, Kuching, Sarawak. The staff from the Institute For Medical Research, Kuala Lumpur, MOH Malaysia also participated in these activities. The study design, training of the field MOH Malaysia staff, data analysis and preparation of the manuscript were conducted by the MOH Malaysia staff in collaboration with VBC.