global fight against mosquitoes and the diseases they carry is stalling.
For decades, the deployment of anti-mosquito tools, including insecticides and bed nets, helped alleviate the burden of diseases like malaria and dengue. But in recent years, progress has slowed, and even reversed, as mosquito populations evolve around these interventions. Climate change is stoking the spread of mosquito-borne disease too, as shifting temperatures expand skeeters’ range. Last year, the U.S. saw its first locally transmitted case of malaria since 2003, and this year, dengue is spreading in record numbers around the world.
“We have all these tools, medicines, bed nets, but the disease is still there,” says Lea Paré Toe, a social scientist with the non-profit Target Malaria in Burkina Faso. “That’s why we need research to come up with new tools that can boost elimination.”
That research is well underway—from efforts to enlist the help of common parasites to tinkering with mosquito genes. Some new tools are already in use, while others are still years from being approved by regulators. But all show promise and could play important roles in a new era of mosquito control that’s potentially easier on the environment than chemical pesticides.
Blocking transmission with a parasite
One promising new tool comes not from a lab, but from nature.
Wolbachia are parasitic bacteria that infect about half of all insect species. The parasite is so ubiquitous, in part, because it can manipulate host reproduction to its own benefit. Infected mothers pass Wolbachia down to all her female and male offspring. When those males mate with an uninfected female, the parasite essentially kills the eggs, hastening Wolbachia’s spread through the population.
Aedes aegypti mosquitoes aren’t naturally infected. But in 2009, entomologist Scott O’Neill and colleagues discovered that Wolbachia infection rendered mosquitoes largely incapable of transmitting many pathogens, including dengue, zika, and even malaria.
It’s still unclear how Wolbachia inhibits transmission. But that hasn’t stopped the World Mosquito Program, a non-profit headed by O’Neill, from developing and testing a mosquito control program that breeds Wolbachia-infected mosquitoes (by carefully injecting Wolbachia into eggs) and releases them into affected areas.
Since 2011, the program has released millions upon millions of mosquitoes in Australia, Indonesia, Brazil and 11 other countries in field trials. “We usually keep releasing until we get to a threshold of about 60 percent of mosquitoes having Wolbachia,” says O’Neill. “At that point, we stop and Wolbachia does the rest by itself.” In many regions, Wolbachia-mosquitoes can represent up to 90 percent of a population within several years, and don’t require future releases.
A 2021 field trial in Yogyakarta, Indonesia, Wolbachia mosquitoes helped drive down dengue cases and hospitalizations by 77 and 86 percent. In parts of Australia, “we’ve essentially eliminated dengue transmission,” said O’Neill.
Wolbachia likely won’t work everywhere, especially areas with extreme temperature swings, O’Neill says. It’s also difficult to inject millions of eggs with Wolbachia and spread them in communities. But a new study suggests drones could speed up distribution, showering up to 160,000 adult mosquitoes per drone from the sky.
Tweaking genes to shrink mosquito numbers
Other techniques take a more direct approach to either sterilize mosquito males or kill biting females before they reach adulthood.
Since the 1950s, researchers have tried sterilizing males with radiation and releasing them into the wild to fool females into mating, shrink the population and reduce disease transmission. But blasting skeeters with radiation can kill males before they get a chance to mate.
Comments
Post a Comment