Bacteria-infected mosquitoes take bite out of deadly dengue

Health Bacteria-infected mosquitoes take bite out of deadly dengue

Nov 24, 2019 12:00 am
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WASHINGTONThey still bite, but new research shows lab-grown mosquitoes are fighting dangerous dengue fever that they normally would spread.

Dengue infections appear to bedropping fast in communities in Indonesia, Vietnam, Brazil and Australia thatare buzzing with the especially bred mosquitoes, an international research teamreported Thursday.

Its the first evidence fromlarge-scale field trials that mosquitoes are less likely to spread dengue andsimilar viruses when they also carry a type of bacteria thats common ininsects and harmless to people.

Rather than using pesticidesto wipe out bugs, this is really about transforming the mosquito, saidCameron Simmons of the nonprofit World Mosquito Program that is conducting theresearch.

The first hint of success camefrom Australia. Mosquitoes bred to carry Wolbachia bacteria were released inparts of North Queensland starting in 2011, and gradually spread through thelocal mosquito population. Dengue is transmitted when a mosquito bites someonewho is infected, and then bites another person, but somehow Wolbachia blocksthatand local transmission has nearly disappeared in those North Queenslandcommunities, Simmons said in an interview.

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

Thursday, Simmonss teamreported a 76-percent decline in dengue recorded by local authorities in anIndonesian community near the city of Yogyakarta since the 2016 release ofWolbachia-carrying mosquitoes. Thats compared to dengue transmission in anearby area where regular mosquitoes do the biting.

Researchers found a similardrop in a community near the southern Vietnamese city of Nha Trang. Andpreliminary results suggest large declines in dengue and a related virus,chikungunya, in a few neighborhoods in Brazil near Rio de Janeiro.

The studies are continuing inthose countries and others. But the findings, presented at a meeting of theAmerican Society for Tropical Medicine and Hygiene, suggest its possible toturn at least some mosquitoes from a public health threat into nuisance biters.

The work marks excitingprogress, said Michigan State University Prof. Zhiyong Xi, who wasnt involvedwith the project but has long studied how Wolbachia can turn mosquitoes againstthemselves.

Reducing disease is the ultimatesuccess of our field, added University of Maryland biologist Brian Lovett, whoalso wasnt part of the project.

More research is needed,specialists cautioned. These studies used local health groups counts of denguecases rather than blood tests, noted Penn State University Prof. ElizabethMcGraw. And while Wolbachia has persisted in North Queensland mosquitoes foreight years and counting, whether mosquitoes maintain dengue resistance thatlong in harder-hit regions remains to be seen.

The results are prettyexcitingstrong levels of reductionsbut there clearly are going to be thingsto be learned from the areas where the reductions are not as great, McGrawsaid.

More than half of insectspecies, from fruit flies to butterflies, naturally are infected withWolbachiabut not the main dengue-spreader, Aedes aegypti mosquitoes.Theyre daytime biters that thrive in hot urban and suburban localities where,for now, widespread pesticide spraying is the main protection.

Researchers with the WorldMosquito Program first injected mosquito eggs with Wolbachia in a lab. Infectedfemales then pass the bacteria on through their eggs. Releasing enoughWolbachia carriers, both the females that bite and the males that dont, allowsmating to spread the bacteria through a local mosquito population.

The approach doesnt reducebites. Simmons said the up-front cost is cheaper than years of spraying andmedical care.

Its just one of multiplenovel mosquito-control methods under study:

  • Michigan States Xi uses Wolbachia in a different wayto eliminate mosquitoes. Release only male Wolbachia carriers and when they mate with uninfected females, the eggs dont hatch.
  • Other researchers zap male mosquitoes with a small dose of radiation, sterilizing them before releasing them into the wild.
  • Genetically modifying mosquitoes is another approach. Furthest in development is Britains Oxitec, which gives male mosquitoes a gene to weaken their offspring so they dont survive to adulthood.

Each approach has pros andcons, but our best hope to control the mosquitoes that make us sick is to boxthem in with multiple technologies, said Marylands Lovett. AP

Image Credits: AP/Silvia Izquierdo, File