Scientists use gut bacteria to prevent mosquito-borne diseases

Chinese scientists have developed a more natural strategy to prevent mosquito-borne diseases by changing insects' gut microbes, which might be used as an alternative to controversial experiments that see genetically-modified mosquitoes released in Florida.

Mosquito-borne viruses, such as dengue and Zika, cause several potentially fatal human viral infections. Dengue viruses infect approximately 390 million each year globally.

An epidemic survey over the past decade documented frequent dengue outbreaks in Xishuangbanna and Lincang, both in southwest China's Yunnan Province. But few have been reported in neighboring cities of Wenshan and Pu'er.

The marked different prevalence stimulated the curiosity of researchers from Tsinghua University and the Yunnan Academy of Animal Science and Veterinary Sciences.

Gut microbes

The team's field investigation on thousands of blood-sucking female mosquitoes revealed that mosquitoes from two different habitats carry different symbiotic bacteria in their guts, the first tissue organ usually infected by viruses.

Among the 55 strains isolated, a kind of bacterium called Rosenbergiella_YN46 was abundant in mosquito guts in Wenshan and Pu'er, but not in Xishuangbanna and Lincang, according to the study published on Friday in the journal Science.

Then, the researchers colonized the strain in the intestines of two common disease-transmitting mosquitoes - Aedes albopictus and Aedes aegypti.

Those mosquitoes did become less likely to be infected with dengue and Zika via blood bites, according to the study.

The further analysis suggested that an enzyme secreted by the bacteria can convert glucose into gluconic acid and rapidly acidify the intestines of blood-sucking mosquitoes. The mosquito-borne viruses will be neutralized in an acidic environment.

Intervention tactics

The team made an experiment in the wild to breed "good mosquitoes" that do not transmit viruses. They added Rosenbergiella_YN46 bacteria to the water where mosquitoes eggs were laid and hatched.

Encouragingly, the intestinal colonization proved a success at a site in Mengla County of Xishuangbanna and the colony persistently resided in the guts of Aedes mosquitoes.

The researchers also proposed another potential intervention strategy - the use of plants. Mosquito's gut microbes in the wild are either derived from microbes in breeding waters, or in the sap and nectar of plants.

"We are collecting a large number of plant samples in Wenshan, where the bacterium was isolated, in order to find plants that are enriched with this bacterium," said Cheng Gong from Tsinghua, the corresponding author of the paper. "Transplanting and cultivating this plant to the infected area may intervene in the ability of mosquitoes to carry and transmit the virus."

"If those plants are shrub or herbaceous plants, they can be grown in your backyard or residential compound," added Cheng.

"Rosenbergiella_YN46 is derived from the natural environment and its potential environmental risk is relatively low, and will not make mosquitoes resistant to the drug, nor affect their survival in nature," commented Xu Jianguo from the Chinese Center for Disease Control and Prevention, who did not participate in the study.

Meanwhile, the team is conducting a study in Leizhou Peninsula in south China's Guangdong Province, where the mosquito population is large but there is no dengue, to discover more bacteria that could inhibit the spread of mosquito-borne viruses.

"The spread of Zika and epidemic encephalitis B might be contained if more bacteria can be found," said Cheng.

This study has shown that the use of bacteria-colonized field mosquitoes could offer a feasible biocontrol strategy for reducing virus transmission and prevalence in nature, said the researchers.

(Cover image via CFP)