Brazilian researchers in Rio de Janeiro have released thousands of mosquitoes infected with bacteria that suppress dengue fever. The hope is they will multiply, breed and become the majority of mosquitoes, thus reducing cases of the disease.
The bacterium Wolbachia is found in 60% of insects. It acts like a vaccine for the mosquito which carries dengue, Aedes aegypti, stopping the dengue virus multiplying in its body. Wolbachia also has an effect on reproduction. If a contaminated male fertilises the eggs of a female without the bacteria, these eggs do not turn into larvae.
If the male and female are contaminated or if only a female has the bacteria, all future generations of mosquito will carry Wolbachia. As a result, Aedes mosquitoes with Wolbachia become predominant without researchers having to constantly release more contaminated insects.
Dengue re-emerged in Brazil in 1981 after an absence of more than 20 years. Over the next 30 years, seven million cases were reported. Brazil leads the world in the number of dengue cases, with 3.2 million cases and 800 deaths reported in the 2009-14 period.
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