Scientists are thinking laterally in an attempt to combat one of Africa's worst killers – malaria. Using nature to fight nature, a new study has shown that fungi have the potential to stop malaria transmission. Two separate experiments reported in the journal Science have found that fungi already on the market as biopesticides can infect adult malaria-carrying mosquitoes and kill them.
Researchers from the University of Edinburgh and Imperial College found that the fungus Beauveria bassiana could reduce the number of mosquitoes able to transmit mamalaria by a factor of about 80.
Homing in this species because of its ability to infect a range of insects, the scientists sprayed cardboard pots with an oil laden with fungal spores. Mosquitoes become infected with the fungus simply by resting on the pots. Death is slow, but as it takes about two weeks for a mosquito to start transmitting the malarial parasite after it is first infected, this is not really a factor. Mosquitoes infected with the fungus died much faster than uninfected mosquitoes, and were less likely to look for a blood feed.
This would also reduce the transmission of the malarial parasite. Other researchers took to the field in Tanzania with another biopesticide, Metarhizium anisopliae. Black sheets were sprayed with the fungal spores and hung in the roof of traditional houses in a rural village. Over the course of three weeks, 23 percent of the mosquitoes caught in the experimental houses became infected with the fungus and died a premature death.
The researchers estimated that if they increased the area covered by the spray and improved its formulation they could infect half the mosquitoes in the house with the fungus. With only half the mosquito population succumbing to the fungal spores, their calculations show that the rate of malaria transmission could be lowered by 96 percent. Using a biological control agent to fight malaria has only been done previously with mosquito larvae, where a bacterium is sprayed onto water.
Using a fungus as a biocontrol agent has the advantage that mosquitoes do not have to ingest the fungus – it penetrates directly into their system through body parts in contact with the spores. Using a known biopesticide also means that some research has already been performed on the fungus prior to its sale to consumers.
The research also has added value because mosquitoes in some areas are becoming resistant to the ordinary insecticides used to control them. Although optimistic about this potential new weapon in the malaria war, the scientists have warned that at best it would take about two years to commercialise these findings.