Dengue infections appear to be dropping fast in communities in Indonesia, Vietnam, Brazil and Australia that are buzzing with the specially bred mosquitoes, an international research team reported Thursday.

It's the first evidence from large-scale field trials that mosquitoes are less likely to spread dengue and similar viruses when they also carry a type of bacteria that's common in insects and harmless to people.

Rather than using pesticides to wipe out bugs, "this is really about transforming the mosquito," said Cameron Simmons of the nonprofit World Mosquito Program that is conducting the research.

The first hint of success came from Australia. Mosquitoes bred to carry Wolbachia bacteria were released in parts of North Queensland starting in 2011, and gradually spread through the local mosquito population.

Dengue is transmitted when a mosquito bites someone who is infected, and then bites another person, but somehow Wolbachia blocks that - and local transmission has nearly disappeared in those North Queensland communities, Simmons said.

The real test would come in dengue-plagued areas in Asia and Latin America that regularly experience outbreaks where millions get the painful and sometimes deadly disease.

Simmons' team has reported a 76 per cent decline in dengue recorded by local authorities in an Indonesian community near the city of Yogyakarta since the 2016 release of Wolbachia-carrying mosquitoes.

Researchers found a similar drop in a community near the southern Vietnamese city of Nha Trang.

Preliminary results also suggest large declines in dengue and a related virus, chikungunya, in a few neighborhoods in Brazil near Rio de Janeiro.

The studies are continuing in those countries and others. But the findings, presented at a meeting of the American Society for Tropical Medicine and Hygiene, suggest it's possible to turn at least some mosquitoes from a public health threat into nuisance biters.

More than half of insect species, from fruit flies to butterflies, naturally are infected with Wolbachia - but not the main dengue-spreader, Aedes aegypti mosquitoes. They're daytime biters that thrive in hot urban and suburban localities where, for now, widespread pesticide spraying is the main protection.

Researchers with the World Mosquito Program first injected mosquito eggs with Wolbachia in a lab. Infected females then pass the bacteria on through their eggs. Releasing enough Wolbachia carriers, both the females that bite and the males that don't, allows mating to spread the bacteria through a local mosquito population.

Simmons said the up-front cost is cheaper than years of spraying and medical care.

Australian Associated Press