Larvicide auto-dissemination by mosquitoes reduces dengue cases in Belo Horizonte

A project developed by researchers from the Leônidas and Maria Deane Institute (Fiocruz Amazônia) and the René Rachou Institute (Fiocruz Minas), in collaboration with the Municipal Health Department of Belo Horizonte, shows that the "auto-dissemination" of larvicides by urban mosquitoes can help control diseases transmitted by these same mosquitoes, such as dengue. The project distributed an average of 2,500 "Larvicide Dissemination Stations" (EDLs) across nine neighborhoods in Belo Horizonte over two years. The intervention reduced the incidence of dengue by 29% in these neighborhoods and by 21% in adjacent neighborhoods, compared to the remaining 258 in the city. The results were published in the journal The Lancet Infectious Diseases. In July, the EDL technology was officially recognized by the Federal Government as one of the new national strategies for controlling the main dengue vectors, Aedes aegypti and Aedes albopictus.

"Our trial demonstrates the effectiveness of the method in controlling dengue. Previous studies have shown the effects of larvicide auto-dissemination on mosquito populations, but without directly assessing the epidemiological impact," explains Sérgio Luz, coordinator of the Center for Pathogens, Reservoirs and Vectors in the Amazon (PReV Amazônia) and lead researcher of the study, together with researchers Fernando Abad-Franch and José Joaquin Carvajal Cortes, both affiliated with the PReV Amazônia Center.

The auto-dissemination strategy uses the mosquitoes themselves to transfer larvicide particles from the ELDs to untreated breeding sites directly. "The mosquitoes act as a sort of "pollinators" that carries the larvicide powder to other breeding sites, which are often not reached by traditional control efforts – such as those located in closed buildings or vacant lots, or simply because they are small and very difficult to find. No one knows better than the mosquito itself the right places for laying its eggs," says Luz.

Sergio Luz points out that the team of researchers has shown, in previous work, that this larvicide auto-dissemination can reach breeding sites located at distances of up to 400 meters, reducing the abundance of urban mosquitoes in both the Amazon and central Brazil. "Now," the researcher explains, "we have shown that this impact on the vectors translates into a significant decrease in the number of dengue cases." 

According to the study, the fact that incidence of dengue also decreased, albeit more modestly, in the neighborhoods adjacent to the intervention areas suggests that the mosquitoes disseminate the larvicide beyond the boundaries of areas where the EDLs are installed. This mobility of the vectors, however, also means that there was likely an influx of mosquitoes from untreated neighborhoods into the intervention area, somewhat reducing the effectiveness of the EDLs.

Less impact on health systems

To measure the impact that a 29% reduction in the incidence of dengue could have on public health systems, the article highlights that, in a typical scenario of an epidemic outbreak with 100,000 cases of the disease, the use of EDLs could relief pressure on the healthcare system by around 29,000 symptomatic cases. 

In the future, and with the continued support of the Ministry of Health, including the Health and Environmental Surveillance Department, the General Coordination of Arboviruses, and Fiocruz, the team plans to replicate the field trials in other cities and in different environmental and socioeconomic contexts. 

Ongoing research is also assessing the possibility of using EDLs' technology with alternative larvicides – which could be crucial for managing any potential emergence of vectors resistant to the molecule currently used – and the development of more practical and user-friendly EDLs. While the results of these new lines of research become available, the work carried out by the Fiocruz team and its partners since 2011 offers a new tool for controlling urban mosquitoes and the diseases they transmit.

Strategy incorporated by the Ministry of Health.

Last Wednesday, the Ministry of Health announced a new action plan to reduce the impact of dengue and other arboviruses in Brazil. On that occasion, the Ministry announced that it will expand the use of Larvicide Dissemination Stations to control Aedes aegypti, the transmitter of dengue, in Brazilian outskirts. The government emphasizes that the strategy, developed and coordinated by researchers from Fiocruz Amazônia, has been tested and approved with proven results in 14 Brazilian cities from different regions, where it was implemented between 2017 and 2020.