Researchers are reporting success in using bacteria-carrying mosquitoes to fight dengue fever. Tests involving the release of laboratory-grown mosquitoes led to sharp drops in dengue cases in several countries.

　　Dengue infections appear to be dropping fast in communities in Indonesia, Vietnam, Brazil and Australia, an international research team reported.

　　The results represent the first evidence from large field trials aiming to test the effectiveness of the bacteria-carrying insects. The kind of bacteria they carry is common in insects but harmless to people.

　　Dengue spreads when a mosquito bites an infected person and then bites someone else. But the mosquitoes that were given the bacteria do not seem to pass on the disease.

　　Cameron Simmons is with the not-for-profit World Mosquito Program, which carried out the research. He told The Associated Press that the tests are an example of efforts to move away from using pesticides as a way to kill insects. "This is really about transforming the mosquito," Simmons said.

　　The first signs of success came in Australia. Mosquitoes produced to carry the Wolbachia bacteria were released in parts of North Queensland beginning in 2011. Over time, the insects spread through the local mosquito population. Health officials in those communities reported that the local spread of dengue had nearly disappeared, Simmons said.

　　Next, researchers found success in areas of Asia and Latin America, where large dengue outbreaks are common. Millions of people in these areas have caught the painful and sometimes deadly disease.

　　Scientists released Wolbachia-carrying mosquitoes in an Indonesian community near Yogyakarta in 2016. Simmons' team reports that the community has since seen a 76-percent decrease in dengue numbers, compared to a nearby area where regular mosquitoes continued to bite.

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

　　Early results also suggest large reductions in dengue and a related virus in a few neighborhoods in Brazil, near Rio de Janeiro.

　　Studies are continuing in these and other countries. But the findings suggest it is possible to turn at least some mosquitoes from a public health threat into dengue fighters.

　　The latest results mark "exciting progress," said Michigan State University professor Zhiyong Xi, who was not involved with the project. He has led his own studies on how Wolbachia can turn mosquitoes against themselves.

　　Reducing disease "is the ultimate success of our field," said University of Maryland biologist Brian Lovett. Lovett also was not part of the project.

　　Experts say more research is needed to confirm the methods and results. Elizabeth McGraw is an expert on the subject at Penn State University. She noted that the latest research used local health groups' counts of dengue cases rather than blood tests.

　　"The results are pretty exciting - strong levels of reductions - but there clearly are going to be things to be learned from [these] areas where the reductions are not as great," McGraw told the AP.

　　More than half of insect species -- from fruit flies to butterflies -- are naturally infected with Wolbachia. But the main spreaders of dengue, Aedes aegypti mosquitoes, are not. They are daytime biters who do well in hot, highly populated areas where widespread pesticide spraying has been the main method of protection.

　　I'm Bryan Lynn.

　　The Associated Press reported on this story. Bryan Lynn adapted the report for VOA Learning English. Ashley Thompson was the editor.

　　We want to hear from you. Write to us in the Comments section, and visit 51VOA.COM.