Bacteria living in the guts of certain mosquitoes block the development of malaria-causing parasites, new research shows.
This may provide a new approach for fighting malaria, which kills a million people each year, the majority of whom are children under the age of five.
“We could use it as a very cost effective bio-control strategy,” said George Dimopoulos, one of the authors of the study.
The researchers began by isolating bacteria that live inside the guts of wild mosquitoes collected from southern Zambia. Malaria is endemic in Zambia, and according to the World Health Organization, responsible for 15% of all deaths in children under five.
“Similarly to humans, mosquitoes harbour a variety of bacteria in their gut,” said Dimopoulos, “and we tested the ability of these bacteria to influence the mosquito’s resistance to the malaria parasite.”
Malaria parasites enter the mosquito’s gut when it takes a blood meal from an infected person. The parasite must then go through several developmental stages before it can be transmitted to the next person the mosquito feeds on.
The researchers found that one species of bacteria in the ‘Enterobacter’ group, which lives naturally inside certain species of mosquito, was particularly potent in blocking the development of malaria parasites.
“The inhibitory effect was very strong. We could inhibit the malaria parasite’s development by up to 99% in the mosquito gut and in the test tube,” said Dimopoulos.
Moreover, the experimenters infected mosquitoes far more heavily with parasites than most insects are in the wild. Thus, if anything, the inhibitory effect may be an underestimate.
“We believe that this bacterium in nature would have 100% blocking activity,” said Dimopoulos.
The blocking effect was independent of the mosquito, occurring equally well in a test-tube as when inside the mosquito’s gut.
Although the exact mechanism of inhibition is not yet known, it seems to involve the production of toxic molecules called ‘reactive oxygen species’ by the bacteria.
“[Reactive oxygen species] in general can cause DNA damage, they can damage the membranes and the proteins of cells, so there are a variety of ways by which these molecules can damage the parasites,” said Dimopoulos.
The bacteria probably produce these toxins as a by-product of their metabolism. It’s also possible they help the Enterobacter to compete against other bacteria inside the mosquito gut.
The researchers’ future work will aim to modify the bacteria so they can flourish in all species of malaria-transmitting mosquitoes, rather than only a select few.
The hope is that wild mosquitoes will then ingest the modified bacteria, perhaps by using sugar baits loaded with the microbes. This would block malaria parasite development on a large scale, reducing the incidence of human infection.
We’re still a long way off that at the moment, as Dimopoulos cautioned, “we would have to spend the next 4-5 years performing laboratory and field experiments before we could implement this in nature.”
Nevertheless, it is a promising step towards a novel weapon in the fight against this deadly disease.
George Dimopoulos explains what these parasite-blocking bacteria are, and how they could be used to help stop malaria...