Researchers have stumbled upon a bacterium naturally found in the mosquito gut that inhibits the growth of the parasite that causes the most deadly form of malaria. The bacterium is unlikely to develop resistance and could therefore be easily introduced into the wild to complement existing malaria eradication strategies.
Malaria, a mosquito-borne disease, is caused by five protozoan parasites, of which Plasmodium falciparum is the deadliest and the most prevalent parasite on the African continent. Unlike other protozoa, P. falciparum infects all types of red blood cells, from immature young cells to old cells. If left untreated, Plasmodium falciparum malaria can become severe and lead to death within 24 hours.
The impact of malaria is well recognized, but little progress has been made in reducing deaths from malaria. According to the latest report from the World Health Organization (WHO), there will be 249 million malaria cases in 2022, compared with 244 million cases in 2021. Now, researchers have stumbled upon a bacterium that prevents the Plasmodium falciparum parasite from developing in the female mosquitoes that transmit malaria.
As part of GlaxoSmithKline's (GSK) research to develop new drugs, researchers studying a group of mosquitoes found that they were becoming increasingly difficult to infect with Plasmodium falciparum. By taking a closer look at mosquitoes and their breeding environment, they found that the insects carry a strain of symbiotic bacteria called Delftiasuruhatensis TC1 that slows the growth of protozoa in the mosquito's gut, where they normally develop before traveling to the salivary glands.
To study the possibility of preventing the spread of Plasmodium in other mosquitoes, the researchers conducted laboratory experiments in which female mosquitoes were given blood containing D. tsuruhatensis TC1, a bacterium that is normally present in low numbers in the mosquito gut. During the experiment, the amount of TC1 increased about 100-fold and was seen in all mosquitoes. Once ingested, P. falciparum oocyst formation is inhibited by up to 73%, and development ceases for at least 16 days and possibly for life. Infectivity is also greatly reduced and only 33% of mice became infected with Plasmodium after being bitten by a mosquito carrying the bacterium.
The presence of D.tsuruhatensisTC1 did not affect the lifespan of the insects themselves; they still produced the same number of eggs. It also has no significant effect on their blood-sucking abilities. When D.tsuruhatensisTC1-infected mosquitoes feed on blood, the bacteria are not released into the feeders, suggesting that D.tsuruhatensisTC1 is also not transmitted to humans through bites.
Molecular analysis showed that the bacterium's action was due to the production of an active molecule called harmane, which the researchers found could be absorbed through the insect's outer surface (cuticle) and digested.
Field studies in Burkina Faso, West Africa, showed that mosquitoes obtained the bacterium from the wild were colonized by D. tsuruhatensis TC1 as well as or even more efficiently than lab-raised mosquitoes. Field studies combined with mathematical modeling show that D.tsuruhatensisTC1 has the potential to be used in conjunction with existing strategies to improve malaria eradication efforts. Additionally, because the bacterium has not been genetically modified and is part of the mosquito's normal microbiome, the insects are unlikely to become resistant to it.
Alfonso Mendoza-Losana, one of the study's co-authors, said: "The discovery of a bacterium that blocks the development of the parasite stage in mosquitoes without affecting the mosquito provides a new approach because it is not harmful to mosquitoes, so there is a low chance of developing resistance. In addition, it is a non-GMO bacterium and can be quickly introduced in the field." "
The research was published in the journal Science.