In Rio de Janeiro, scientists have released thousands of mosquitoes infected with a bacteria that will hopefully suppress dengue fever. The theory is that the genetically modified yellow fever mosquitos (Aedes aegypti) will breed with the existing population and become the dominant type, thus eliminating the disease spreading variants.
Dengue is one of the most widespread and rapidly spreading mosquito-borne diseases in the world, with a 30-fold increase in global incidence over the past 50 years. So far Aedes aegypti have proved difficult to control with insecticides and more traditional methods. However it was discovered that A. aegypti transinfected with the wMel strain of Wolbachia showed limited dengue virus (DENV) replication. Virus-blocking persists in Wolbachia-infected mosquitoes after their release and establishment (like a vaccine). This, coupled with the ability of Wolbachia to both induce pathogen interferences and spread into mosquito vector population (i.e. become dominant) makes them ideal bio-control agents.
To achieve population suppression of Aedes aegypti using the RIDL system (Release of Insects carrying a Dominant Lethal), a large number of male mosquitos need to be released. This requires mass rearing techniques to obtain the highest quality males. RIDL is effective and an environmentally safe method of controlling mosquitoes, with no knock on effect to non-target organisms such as natural enemies.
Brazil leads the world in the number of dengue cases, with 3.2 million cases and 800 deaths reported in the 2009-14 period. Brazil has released around 11 million males in the 2012 programme, and part of the programme is also taking place in Australia, Vietnam and Indonesia.