Science Policy Around the Web June 29, 2021

By Trisha Tucholski, PhD

Image by 41330 from Pixabay

Mosquitos armed with virus fighting bacteria sharply curb dengue infections, hospitalizations

Dengue is a burdensome mosquito-borne disease, with 100 to 400 million infections per year predicted by the World Health Organization (WHO). The disease, caused by infection with dengue virus, causes high fever and severe joint pain in infected individuals. Insecticides have failed to control dengue in tropical regions. Luckily, scientists have identified a strategy to reduce dengue infections in humans by infecting mosquitos with a bacterium that prevents the virus from replicating, making its spread by mosquitos less likely. While evidence for the effectiveness of this strategy was reported in 2019, a controlled and randomized study was required to convince the global scientific community of its effectiveness in reducing human disease. Ultimately, results from the trial, which released mosquitos infected with Wolbachia pipientis in the Indonesian city of Yogyakarta, showed that the infected mosquitos reduced dengue infection and hospitalization.

In the large-scale controlled and randomized trial, scientists from the nonprofit World Mosquito Program (WMP) divided Yogyakarta (26-square kilometers, 300,000 residents) into 24 segments. Every 2 weeks for a period of 18 to 28 weeks, mosquito eggs carrying Wolbachia were released in half of the segments. The remaining half of the segments were used as control areas. By 10 months post-release, Wolbachia had spread to at least 80% of mosquitos in the treated areas. To study how the bacteria-infected mosquitos affected dengue infection rates in the area, the scientists recruited participants from primary care clinics in the city who came in with fever. The results of the study were published in The New England Journal of Medicine and reported that patients living in treated clusters were infected with dengue at a rate of 2.3%, whereas those who lived in control areas were infected at a rate of 9.4%. This is a 77% reduction in dengue infections. Importantly, hospitalization for dengue was reduced by 86%.

Wolbachia protects against the four main subtypes of dengue viruses that infect humans. The bacteria naturally infects insects, but not Aedes aegypti, which is the primary vector for dengue virus and other similar viruses which cause human disease (e.g. Zika virus). A scientist familiar with the study indicated it is promising, but reminds that it is important to monitor the mosquitos, bacteria, and viruses for genetic mutations that can could impact effectiveness of the strategy in the long-term. WMP presented the promising data to the WHO in December 2020, and the WHO is expected to recommend broader use of the strategy. Currently, the approach costs less than $10 per person protected, but the WMP would like to reduce the cost to less than $1.

(By Kelly Servick, Science)

Science Policy Around the Web June 29, 2021