Two new approaches targeting mosquitos offer promising ways to limit the spread of malaria, according to two studies published last week in Science. In both, researchers manipulate mosquitoes' abilities to host the malarial parasite Plasmodium falciparum.
Malaria is one of the deadliest diseases in the world, is endemic in more than 106 countries, and kills 400,000 people annually. The disease is deadliest in children under the age of 5 years. It's spread by female Anopheles mosquitoes carrying Plasmodium.
Modifying mosquitoes, the vectors that transmit the parasite, has long been a goal of malaria control, and the new studies offer inroads into introducing disease-preventing mechanisms into the insects.
Midgut bacteria that prevent Plasmodium
The studies originated at Johns Hopkins Bloomberg School of Public Health's Malaria Research Institute. The first looked at using a strain of nonpathogenic bacteria, Serratia AS1, to harmlessly invade the mosquito's midgut without otherwise affecting the insect's life cycles.
Unlike other mosquito control efforts, AS1 offers an easy and efficient way to control both existing and future generations of mosquitos.
"Although engineered symbiotic bacteria have been shown to render mosquitoes resistant to the parasite, the challenge remains to effectively introduce such bacteria into mosquito populations," the authors write, noting that AS1 did not alter mosquito mating patterns. "Rapid spread of AS1 through wild populations could plausibly occur by dissemination in mosquito breeding water."
After introducing AS1 into 5% of a mosquito population in laboratory cage experiments, 100% of the insects had AS1 after two generations. The AS1 bacteria spread in populations both sexually and genetically, or horizontally and vertically, suggesting long-term and self-sustaining protection from plasmodium.
GM mosquitoes exist for generations
A second study showed that mosquitoes with genetically modified microbiota, used to enhance their immune response to malaria parasites, were able to reproduce and pass on the genetically modified (GM) trait for up to three generations.
According to a press released from the National Institute of Allergy and Infectious Diseases (NIAID), even combining 10% GM with 90% wild mosquitoes, the Plasmodium-resistance trait dominated after a few generations and conferred resistance to the malaria parasite for 7 years.
The authors believe that changing the microbiota of the mosquitoes altered their scent, making them more sexually attractive to other insects and allowing the GM traits to become valued within the mosquito population.
The results suggest that GM mosquitos can compete within wild mosquito populations.
See also:
Sep 29 Science AS1 study
Sep 29 Science microbiota study
Sep 28 NIAID press release
Sep 28 Johns Hopkins press release
