Dengue epidemics can occur annually and are caused by specific mosquitoes, but introducing bacteria to the mosquitoes can reduce the transmission of the infection.
Deploying treated mosquitoes designed to curb dengue fever was successful in reducing incidence in an Indonesia city by 77 percent, according to a paper published in The New England Journal of Medicine.
Investigators from Indonesia conducted a cluster-randomized trial in order to test the efficacy of releasing wMel-infected A. aegypti mosquitoes on the control of dengue in Yogyakarta, a city in Indonesia. A. aegypti mosquitoes are the primary drivers of dengue, a mosquito-borne virus that can cause epidemics on multiyear intervals, the study authors explained.
The investigators added that a maternally inherited bacteria called Wolbachia pipientis does not occur naturally in A. aegypti mosquitoes, but it can be introduced and used as a method of curbing dengue using the wMel strain. After getting approval from the leaders of 37 urban villages, the investigators randomly assigned 12 geographic clusters to receive deployments of the wMel-infected A. aegypti mosquitoes and 12 clusters received no deployments.
In 2013, this research team found that these mosquitos were less likely than others to transmit dengue.
To assess the intervention, the study authors used a test-negative design and patients aged 3 to 45 years with acute fever who presented to local primary care clinics were recruited. The 8144 patients then underwent laboratory testing to virologically confirm dengue. Of the total patient group, 3721 lived in intervention clusters and 4423 lived in control clusters, the study authors found.
To be eligible, the participants also had to reside in the trial area every night for the 10 days preceding the onset of illness. If the participants had localizing symptoms linked to a specific diagnosis (such as diarrhea, otitis, or pneumonia) or were enrolled in the trial within the previous 4 weeks, they were excluded.
The study authors reported 4 cases of virologically confirmed chikungunya, and those patients were excluded. One patient came from the intervention cluster and 3 came from the control clusters. Additionally, the investigators noted, there were zero cases of Zika detected.
Virologically confirmed dengue was observed in 67 of 2905 participants in the intervention clusters (2.3 percent) compared to 318 of 3401 participants in the control clusters (9.4 percent), the study authors reported. Ultimately, the study authors calculated the protective efficacy of the wMel-infected A. aegypti mosquitoes intervention was 77.1 percent. This rate was similar among 4 dengue virus serotypes, the study authors also added.
Hospitalization incidence for virologically confirmed dengue was lower among patients in intervention clusters when compared to control clusters as well: 0.4 percent vs. 3.0 percent, respectively. The study authors calculated this protective efficacy to be 86.2 percent. This lower incidence was found across all participant clinics, the study authors said. They also reported no participants died between enrollment and follow-up.
“It is reassuring that protective efficacy was observed against all 4 dengue serotypes and with the greatest confidence observed against DENV-2 and DENV-4, since these were the most prevalent serotypes,” the study authors wrote, adding that their findings in terms of efficacy are consistent with laboratory and field observations.
In the future, the investigators suggested, this method should be tested as a way to curb transmission of other diseases, such as Zika, chikungunya, yellow fever, and Mayaro viruses by A. aegypti.