Wolbachia-infected mosquitos decreased the incidence of symptomatic dengue fever

1. Areas with Wolbachia-infected mosquitos were shown to decrease the incidence of dengue fever.

2. Hospitalizations for dengue fever decreased in areas where Wolbachia-infected mosquitos were deployed.

Evidence Rating Level: 1 (Excellent)  

Study Rundown: Dengue fever is a mosquito-borne illness and is classified as one of the top ten global threats according to the World Health Organization. Aedes aegypti are the primary carriers of dengue. It was previously shown that A. aegypti mosquitos infected with Wolbachia pipientis – an obligate intracellular bacterium – are less likely to transmit dengue compared to the wild-type mosquito. This study compared the amount of virologically confirmed dengue (VCD) cases that occurred in geological clusters that were randomly assigned to receive either Wolbachia-infected mosquitos or no deployments. The study demonstrated that VCD occurred less in the intervention clusters compared to the control clusters. Furthermore, it was shown that hospitalization for VCD was also lower in the intervention clusters compared to the control clusters. As people were free to move across clusters, a limitation of this study was not being able to account for an individual’s exposure to the infected or regular mosquitos. Nonetheless, the study’s findings are significant for the use of Wolbachia-infected mosquitos to control the spread of dengue fever.

Click to read the study in NEJM

Relevant Reading: Stable introduction of a life-shortening Wolbachia infection into the mosquito Aedes aegypti

In-Depth [randomized controlled trial]: This cluster randomized-controlled trial enrolled 6,306 participants at 18 primary care clinics in Indonesia. Patients presenting with a fever, between the ages of three and 45 years, and who had resided in the trial area for the past ten days were eligible for the trial. Patients were excluded if they presented with other localized symptoms suggesting a different diagnosis. Dengue virus was confirmed by either reverse-transcriptase-polymerase-chain-reaction (RT-PCR) or by an enzyme-linked immunosorbent assay (ELISA). A total of 24 clusters were created from a contiguous urban area of 26km² with geographical borders that would slow the mosquito dispersion between clusters. The cluster randomization occurred in a 1:1 ratio to either receive Wolbachia-infected mosquitos or no deployment, respectively. The primary endpoint was symptomatic VCD of any severity. After a maximum of a 21-day follow-up, there were 67 cases (2.3%) in the intervention clusters compared to 318 cases participants (9.4%) in the control clusters (odds ratio [OR], 0.23; 95% confidence interval [95% CI], 0.15 to 0.35; p = 0.004). The protective efficacy of the Wolbachia-infected mosquito deployment was 77.1% (95% CI, 65.3 to 84.0). The incidence of hospitalization was 13 cases (0.4%) in the intervention cluster compared to 102 cases (3.0%) in the control clusters (protective efficacy, 86.2%; 95% CI, 66.2 to 94.3). Overall, the study determined that Wolbachia-infected mosquitos were effective in decreasing the incidence and hospitalizations of dengue fever providing evidence for their use in controlling the viral spread.

Image: PD

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