Brazil has begun releasing mosquitoes immunised against dengue fever in a bid to cut the number of people who contract the illness.

Ten thousand mosquitoes immunised against dengue fever have been released in Brazil as part of an innovative attempt to curb the spread of the tropical viral sickness.

Gabriel Sylvestre Ribeiro said the Aedes aegypti mosquitoes were released in Tubiacanga neighbourhood in northern Rio state.

"We inoculated them in the lab with the Wolbachia bacteria, which block the development of the dengue virus," he said on Thursday.

"We release the 'good mosquitoes' in front of people's houses so that they enter and reproduce with the wild mosquitoes. Their progeny will no longer transmit dengue," which can be fatal, said the biologist.

After two years of research, this is the first time that a Latin American country has tested a method already functioning in Australia, Indonesia and Vietnam, where the first eggs of the dengue-carrying Aedes aegypti mosquitoes inoculated with Wolbachia were imported to Brazil.

The researchers hope to obtain results next year when the majority of the mosquitoes in Tubiacanga should already be immunised and harmless to people.

Brazil has been the country most affected by dengue since 2000, with seven million cases reported. Over the past five years, the sickness has caused about 800 deaths.

The Fiocruz experiment is an addition to a project using genetically modified mosquitoes and will be rolled out to other neighbourhoods and cities.

Copyright AAP 2014.