Establishment of Wolbachia Strain wAlbB in Malaysian Populations of Aedes aegypti for Dengue Control

Abstract

Dengue has enormous health impacts globally. A novel approach to decrease dengue incidence involves the introduction of Wolbachia endosymbionts that block dengue virus transmission into populations of the primary vector mosquito, Aedes aegypti. The wMel Wolbachia strain has previously been trialed in open releases of Ae. aegypti; however, the wAlbB strain has been shown to maintain higher density than wMel at high larval rearing temperatures. Releases of Ae. aegypti mosquitoes carrying wAlbB were carried out in 6 diverse sites in greater Kuala Lumpur, Malaysia, with high endemic dengue transmission. The strain was successfully established and maintained at very high population frequency at some sites or persisted with additional releases following fluctuations at other sites. Based on passive case monitoring, reduced human dengue incidence was observed in the release sites when compared to control sites. The wAlbB strain of Wolbachia provides a promising option as a tool for dengue control, particularly in very hot climates.

Keywords: Aedes; Wolbachia bacteria; arbovirus; dengue; disease reduction; mosquito.

Figure 1

Maps of Six Release Zones (A) Mentari Court. (B) Section 7 Flats and Section 7 Landed. (C) Section 7 Commercial Centre. (D) AU2 landed and AU2 PKNS flats. See also Figure S1.

Figure 2

Ae. aegypti Population Size Estimates at Release Sites Ovitrap index (Ae. aegypti-positive traps divided by total number of traps) measured during the release and monitoring period. Gray shaded areas represent release periods; 95% confidence intervals are shown as dotted lines. See also Figures S2, S3, and S6.

Figure 3

Wolbachia Frequency during and after Releases Monitoring was conducted using ovitrapping and qPCR. (A) Mentari Court. (B) Shah Alam Section 7 Flats. (C) Shah Alam Section 7 Commercial Centre. (D) AU2 Landed. Release numbers are shown in gray shading; 95% confidence intervals are shown as dotted lines. See also Figures S2, S5, and S6.

Figure 4

Dengue Incidence from 2013 in Mentari Court (MH) and Matched Control Sites (M 1–8) The periods during and after commencement of wAlbB-carrying Ae. aegypti releases are indicated by blue (for other sites and their matched controls, see Figure S7). Incidence is calculated as total confirmed dengue cases per total population ^∗ 100,000. See also Figure S7.

Figure 5

Dengue Reduction following Wolbachia Releases Incidence of confirmed human dengue cases for each week of the study period in the six release sites: (A) Mentari Court, (B) Section 7 Flats, (C) Section 7 Commercial Centre, (D) AU2 Landed, (E) AU2 PKNS, and (F) Section 7 Landed. Black lines and gray shaded areas show the posterior mean and 95% credible intervals of the incidence inferred from a Bayesian time series model. Points represent empirical incidences calculated directly from case data. The periods during and after commencement of Wolbachia-carrying Ae. aegypti releases are indicated by blue regions.

Figure 6

Dengue Control Activities (Other Than Wolbachia Release) at the Section 7 Commercial Centre, Mentari Court, and Section 7 PKNS Flats in Release and Matched Control Sites The date of first Wolbachia releases is indicated by the black dashed line, and activities carried out in the year before and year after this date are shown. Data were only available for three release sites. Thermal fogging at the periphery refers to fogging done at nearby construction sites.