Sterilization by radiation plus infection with Wolbachia bacteria in male mosquitoes can go a long way toward lowering the burden of deadly disease.
Mosquitoes, in addition to delivering itchy bites to humans, are a vector for some of the world’s deadliest diseases including malaria, dengue fever, yellow fever, Zika, and chikungunya. Malaria alone kills more than 1 million people annually, mainly children and primarily in sub-Saharan Africa, according to Unicef, with drug-resistant strains growing more common in Southeast Asia. And the incidence of dengue fever is up dramatically in recent years, afflicting 50 million to 100 million people a year worldwide and causing as many as 25,000 deaths annually as a result of dengue hemorrhagic fever.
A team out of Michigan State University has field tested a combination of mosquito sterilization strategies in an effort to lower the global burden of mosquito-borne diseases. The investigators, partnering with the United Nations’ Food and Agriculture Organization, the Vienna-based International Atomic Energy Agency (IAEA), and Sun Yat-Sen University and Guangzhou Wolbaki Biotech, both in China, conducted the 2-year trial on 2 islands in Guangzhou’s Pearl River.
The investigators, led by Zhiyong Xi, PhD, a microbiology and molecular genetics professor at Michigan State University, mass-reared male mosquitoes in a controlled environment and then irradiated them to cause sterilization. This procedure, known as sterile insect technique (SIT), has been used on its own with some success. The irradiated males mate with wild females, who then do not produce any offspring. However, according to an IAEA press release, the challenge has been producing a sufficient number of sterile males for wild females to mate with, in order to prevent them from mating with wild males and reproducing.
A second technique, known as incompatible insect technique (IIT), involves infecting mass-reared mosquitoes with Wolbachia bacteria. This infection results in cytoplasmic incompatibility with other mosquitoes, which means any mating between an infected male and a wild female will not result in offspring—hence the “incompatible” moniker.
In this trial, the investigators were able to nearly eliminate the local population of the Asian tiger mosquito (Aedes albopictus), a prolific disease spreader. After subjecting the mosquitoes to SIT, the team then applied IIT. One of the benefits of using this combination SIT/IIT technique is that Wolbachia on its own partly sterilizes male mosquitoes, meaning they can receive a lower dose of radiation during SIT than would be needed if only SIT were being used. This lower dose of radiation keeps the males attractive enough for females to mate with, which isn’t always the case when a full dose of radiation is used. And using IIT on its own carries the risk that stray females in the mass-reared population would be infected with Wolbachia along with the males, which—because the genders would no longer be cytoplasmically incompatible—would result in offspring should they mate.
Other benefits of using this combination technique is that it’s likely less toxic than spraying insecticides, and the expenses involved in its deployment are reasonable. “Our study predicts that the overall future costs of a fully operational intervention using this environmentally friendly approach will be around $108 per hectare annually, which seems cost effective in comparison with other mosquito control strategies,” Xi said in the press release. A hectare is equivalent to roughly 2.5 acres.
According to the press release, China will soon test this combination mosquito sterilization technology in larger, more urban areas.