Tweaking the genes of mosquitoes that can carry disease can transform those blood suckers into weapons that fight disease. This is the finding of a new study in Brazil.

Dengue （DEN-gay） fever is a viral disease spread by Aedes aegypti mosquitoes. This potentially life-threatening infectious disease causes high fevers， headaches， pain and sometimes mild to severe bleeding. Because there is no cure， health officials are always on the lookout for ways to slow the spread of this virus. And one new approach is to slow the growth of mosquito populations.

By altering the genes in male mosquitoes， researchers have just impaired the ability of these insects to reproduce. Then they released the guys throughout several neighborhoods in the city of Piracicaba. And over the next year， the presence of those altered males put a dent in the towns number of new dengue cases.

Health officials used regular methods to limit new skeeter-breeding grounds throughout much of the city. Such measures included keeping stagnant water from collecting outside of homes in buckets， plant saucers or other spots.

Where such control measures were taken， the number of new dengue cases dropped by 52 percent over a year， beginning in mid-2015. But in neighborhoods where the altered males were released as an extra control， the results were much， much better. Dengue cases there dropped 91 percent — from 133 to a mere 12.

Oxitec is the biotechnology company based in Abingdon， England， that created the altered male insects. It reported that its new data linked the release of those altered male insects with a sharp drop in disease.